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Bahi Takkouche, Carlos Regueira-Méndez, Agustín Montes-Martínez, Risk of cancer among hairdressers and related workers: a meta-analysis, International Journal of Epidemiology, Volume 38, Issue 6, December 2009, Pages 1512–1531, https://doi.org/10.1093/ije/dyp283
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Abstract
Background Hairdressers and allied occupations represent a large and fast growing group of professionals. The fact that these professionals are chronically exposed to a large number of chemicals present in their work environment, including potential carcinogens contained in hair dyes, makes it necessary to carry out a systematic evaluation of the risk of cancer in this group.
Methods We retrieved studies by systematically searching Medline and other computerized databases, and by manually examining the references of the original articles and monographs retrieved. We also contacted international researchers working on this or similar topics to complete our search. We included 247 studies reporting relative risk (RR) estimates of hairdresser occupation and cancer of different sites.
Results Study-specific RRs were weighted by the inverse of their variance to obtain fixed and random effects pooled estimates. The pooled RR of occupational exposure as a hairdresser was 1.27 (95% CI 1.15–1.41) for lung cancer, 1.52 [95% confidence interval (CI) 1.11–2.08] for larynx cancer, 1.30 (95% CI 1.20–1.42) for bladder cancer and 1.62 (95% CI 1.22–2.14) for multiple myeloma. Data for other anatomic sites showed increases of smaller magnitude. The results restricted to those studies carried out before the ban of two major carcinogens from hair dyes in the mid-1970s were similar to the general results.
Conclusions Hairdressers have a higher risk of cancer than the general population. Improvement of the ventilation system in the hairdresser salons and implementation of hygiene measures aimed at mitigating exposure to potential carcinogens at work may reduce the risk.
Introduction
Hairdressers, barbers and beauticians represent an important occupational group, with >800 000 people employed in the USA and ∼1 million in Europe.1,2 In the USA, this figure will grow 14% through 2016, faster than the average of all occupations.1 These professionals are exposed to several thousands of chemicals contained in colorants, bleaches, shampoos and hair conditioners. Furthermore, hairdressers may be exposed to volatile solvents, propellants and aerosols from hair sprays as well as to formaldehyde, methacrylates and nitrosamines contained in many hair care products.3 Several of these chemicals, essentially those contained in hair dyes, are potentially carcinogenic and some of them have been found in the urine of cosmetologists.4,5 Our previous meta-analysis did not show any marked increase in the risk of cancer for personal use of hair dyes.6 However, the fact that exposure to hair dyes is more prolonged in occupational settings, and has a higher concentration and frequency than personal exposure, in addition to the fact that they may be exposed to carcinogens contained in other products than hair dyes, puts hairdressers, barbers and beauticians at higher risk of cancer. The main social partners in the European hairdressing industry have recently expressed their growing concern on occupational diseases and emphasized the fact that hairdressers have no influence on the composition of cosmetic products, in spite of being exposed to them.7
Although some studies found an increased risk of cancer among hairdressers,8,9 others failed to find any association.10,11 The International Agency for Research on Cancer (IARC) reaffirmed recently that occupational exposure of hairdressers and barbers was ‘probably carcinogenic’ and that, globally, there was ‘limited evidence’ on this carcinogenicity.12 An increased risk of cancer among hairdressers and personal appearance workers would cause an important public health concern given the large number of people employed in this sector. To date, no comprehensive meta-analysis has focused on the relation between occupational exposure among hairdressers and allied occupations and the risk of cancer. We therefore sought to explore this issue through a meta-analysis, adhering strictly to the MOOSE guidelines for meta-analyses of observational studies.13
Methods
Search strategy
To identify eligible studies, we systematically searched Medline from 1966 to March 2009 for both English and non-English language articles by applying the following algorithm: (HAIRDRESSER* OR BEAUTICIAN* OR COSMETOLOGIST* OR BARBER*) AND (CANCER* OR NEOPLASM* OR CARCINOGEN*) both in Medical Subject Heading and in free text words. We used similar strategies to search EMBASE (1980–2009) and LILACS databases (Latin America and Caribbean) from 1982 to 2009. We searched meeting abstracts using the ISI Proceedings database from inception to 2009. Furthermore, we manually examined the bibliography of the papers that were retrieved electronically and of recent narrative reviews and monographs on carcinogenic risks of hairdressers.3,14 During a recent expert meeting on the same topic, held at IARC (Lyon, France),15 we contacted scientists working on the subject or reviewing it to identify studies that we had potentially missed in our search. We also searched for unpublished studies and results published in other supports such as internal reports, PhD dissertations and other theses. Finally, in order to complete our search and make it inclusive of those studies that list estimates for hairdressers as secondary exposure only—which may have been thus missed in previous computerized searches—we have checked the tables of every article that considers occupation at large, and not only employment as a hairdresser, as an exposure factor of cancer.
We defined a study unit (or dataset) as the analysis of the relation between occupational hairdressing exposure and cancer of a specific anatomic site. As different anatomic sites may be reported in the same article, a single publication could then report more than one study unit. For the sake of simplification, in this report we use the term ‘study’ as a synonym for study unit or dataset.
All searches were carried out independently by two epidemiologists (B.T. and A.M.M.) and discrepancies were resolved by agreement.
Inclusion criteria and data collection
Studies were included if they met the following criteria: (i) presented original data from case–control, cohort or proportional or standardized mortality or morbidity ratio studies (PMR, SMR); (ii) the outcome of interest was clearly defined as cancer of an anatomical site; (iii) the exposure of interest was occupation as a hairdresser, beautician or barber; and (iv) provided relative risk (RR) estimates and their confidence intervals (CIs) or provided enough data to calculate them (raw data, observed and expected cases in PMR and SMR studies, P-value or variance estimate). Studies on childhood cancers related to the parents’ occupation were not considered. To prevent multiple appearances of the same cohort in our analysis, we grouped the studies so that we could trace the same population. We included the most recent study as it generally provided the longest follow-up and the largest number of cases.
We carried out as many analyses as different anatomical cancer sites were available. Thus, when RRs of cancer of different anatomical sites were available in the same publication, we used this publication several times.
We recorded on a standardized questionnaire study name, year of publication, study design, type of outcome (incidence or mortality), sample size (cases and controls, or number of exposed cases for PMR, SMR and cohort studies), type of controls for case−control studies (hospital or population controls), variables used for adjustment or matching, and effect measures with their corresponding 95% CI.
Quality assessment
As no universal scale is available for measuring quality of observational studies, we followed the recommendations of the MOOSE guidelines and assessed the quality of key components of design separately rather than generate a single aggregate score.13 Following this recommendation, we assessed study quality based on the following five criteria, which contain elements of the Newcastle–Ottawa Quality Scale,16 labelled as ‘yes’ or ‘no’. For a comprehensive assessment of quality, we chose items that could apply to all designs: (i) whether the target population of the study was clearly defined or, on the contrary, the subjects were chosen at convenience; (ii) whether or not the diagnosis of cancer was reliable and included either pathology reports, direct cause on death certificates or information from an established cancer register; (iii) whether or not job assessment was reliable and included duration of employment or job matrix measurement; (iv) whether or not occupation as a hairdresser occurred clearly before cancer onset; and (v) whether or not confounding by smoking was prevented by matching or adjustment. Throughout this assessment, when the information on a specific item was not provided by the authors, we graded this item as ‘no’.
Within each item, we calculated two pooled odds ratios (ORs): one for those studies that were labelled ‘yes’ and one for those labelled ‘no’. As a secondary analysis, we carried out a pooled analysis on those studies that fulfilled more than three criteria and compared with those that scored ≤3.
Quality scoring was performed independently by two reviewers (B.T. and C.R.M.) and the results were merged by consensus. The complete protocol for quality scoring is available upon request from the first author.
Statistical analysis
We weighted the study-specific adjusted log ORs for case−control studies and log RRs for cohort studies by the inverse of their variance to compute a pooled RR and its 95% CI. ORs were considered estimates of RRs. We assumed that the person-time of the unexposed group is much larger than that of the exposed group and thus considered SMRs as equivalent to incidence rate ratios.17
For the same anatomical cancer site, we presented results for mortality and incidence studies separately. Nevertheless, in a second instance, we included incidence and mortality measures of effect together (i.e. SMRs or PMRs and RRs). The difference between mortality RRs and incidence RRs for the same cancer location and exposure is generally small.18
As recommended by methodologic experts, proportional mortality studies were considered as a variant of the case–control design.19
We presented both fixed and random effects pooled estimates, but used preferentially the latter when heterogeneity was detected.
We used a version adapted to small samples of the DerSimonian and Laird Q test to check for heterogeneity.20 The null hypothesis of this test is absence of heterogeneity. To quantify this heterogeneity we calculated the proportion of the total variance due to between-study variance (Ri statistic).20 We further explored the source of heterogeneity by restricting the analysis to subgroups of studies defined by characteristics such as type of study design (case–control or cohort), adjustment factors and quality scale.
We assessed publication bias visually through funnel plots and formal testing using the test proposed by Egger.21 We also performed sensitivity analyses, recalculating the pooled estimates under extreme conditions.
All analyses were performed with the software HEpiMA® version 2.1.320 and STATA version 8.0 (StataCorp LP, College Station, TX, USA).
Results
Our search retrieved 247 studies, published in 67 different articles and carried out in 14 countries, on cancer on 22 different anatomic sites among hairdressers and allied occupations that met our inclusion criteria (Tables 1–5). We did not find any unpublished study.
Study-specific RRs and 95% CIs of gynaecologic cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Breast . | Cervix uteri . | Corpus uteri . | Ovary . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | 0.91 (0.48–1.70) | 1.10 (0.51–2.24) | 1.52 (0.50–3.89) | 2.91 (1.21–6.46) | H | Age, sex | 21/719 |
| Kinlen et al.44 | 0.58 (0.06–2.77) | – | – | – | H/P | Age, sex, marital status, social class | 191/561 |
| Koenig et al.45 | 0.70 (0.14–3.44) | – | – | – | P | Age, sex, family history, age at 1st birth, others | 398/790 |
| Habel et al.46 | 1.5 (0.5–4.8) | – | – | – | P | Age, sex, education, alcohol, body mass index | 537/492 |
| Band et al.47 | 1.05 (0.46–2.41) | – | – | – | P | Age, sex, education, alcohol, smoking, others | 1018/1020 |
| Proportionate mortality or morbidity studies | |||||||
| Menck et al.48 | 1.01 (0.75–1.36) | – | – | – | – | Age, sex | 135 |
| Kono et al.49 | 0.59 (0.19–1.38) | – | – | 1.36 (0.44–3.16) | – | Age, sex, period | 141 |
| Spinelli et al.50 | 0.79 (0.36–15.1) | – | – | 2.04 (0.88–4.03) | – | Age, sex | 39 |
| Lamba et al.51 | 1.11 (1.04–1.17) | 0.96 (0.80–1.14) | 0.94 (0.80–1.10) | 1.02 (0.92–1.14) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Teta et al.52 | 1.02 (0.89–1.17) | 0.80 (0.55–1.13) | 1.23 (0.95–1.56) | 1.34 (0.99–1.78) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 0.56 (0.27–1.17) | 1.90 (0.71–5.06) | – | 0.5 (0.07–3.55) | – | Age, sex, matrimonial status | 65 |
| Kato et al.54 | 1.33 (1.00–1.78) | – | – | – | – | Age, sex | 46 |
| Andersen et al.55 (Denmark) | 1.01 (0.85–1.20) | 1.08 (0.81–1.45) | 1.52 (1.12–2.06) | 1.33 (0.97–1.83) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.03 (0.88–1.21) | 1.26 (0.79–2.00) | 1.24 (0.91–1.68) | – | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.00 (0.80–1.25) | 0.92 (0.58–1.46) | 1 (0.64–1.57) | 0.91 (0.58–1.43) | – | Age, sex, period | 492 |
| Vasama-Neuvonen et al.8 | – | – | – | 1.3 (1.0–1.7) | – | Age, sex, period, social status | 60 |
| Czene et al.56 | 1.02 (0.95–1.09) | 1.28 (1.12–1.47) | 0.91 (0.77–1.08) | 1.11 (0.96–1.28) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Breast . | Cervix uteri . | Corpus uteri . | Ovary . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | 0.91 (0.48–1.70) | 1.10 (0.51–2.24) | 1.52 (0.50–3.89) | 2.91 (1.21–6.46) | H | Age, sex | 21/719 |
| Kinlen et al.44 | 0.58 (0.06–2.77) | – | – | – | H/P | Age, sex, marital status, social class | 191/561 |
| Koenig et al.45 | 0.70 (0.14–3.44) | – | – | – | P | Age, sex, family history, age at 1st birth, others | 398/790 |
| Habel et al.46 | 1.5 (0.5–4.8) | – | – | – | P | Age, sex, education, alcohol, body mass index | 537/492 |
| Band et al.47 | 1.05 (0.46–2.41) | – | – | – | P | Age, sex, education, alcohol, smoking, others | 1018/1020 |
| Proportionate mortality or morbidity studies | |||||||
| Menck et al.48 | 1.01 (0.75–1.36) | – | – | – | – | Age, sex | 135 |
| Kono et al.49 | 0.59 (0.19–1.38) | – | – | 1.36 (0.44–3.16) | – | Age, sex, period | 141 |
| Spinelli et al.50 | 0.79 (0.36–15.1) | – | – | 2.04 (0.88–4.03) | – | Age, sex | 39 |
| Lamba et al.51 | 1.11 (1.04–1.17) | 0.96 (0.80–1.14) | 0.94 (0.80–1.10) | 1.02 (0.92–1.14) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Teta et al.52 | 1.02 (0.89–1.17) | 0.80 (0.55–1.13) | 1.23 (0.95–1.56) | 1.34 (0.99–1.78) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 0.56 (0.27–1.17) | 1.90 (0.71–5.06) | – | 0.5 (0.07–3.55) | – | Age, sex, matrimonial status | 65 |
| Kato et al.54 | 1.33 (1.00–1.78) | – | – | – | – | Age, sex | 46 |
| Andersen et al.55 (Denmark) | 1.01 (0.85–1.20) | 1.08 (0.81–1.45) | 1.52 (1.12–2.06) | 1.33 (0.97–1.83) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.03 (0.88–1.21) | 1.26 (0.79–2.00) | 1.24 (0.91–1.68) | – | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.00 (0.80–1.25) | 0.92 (0.58–1.46) | 1 (0.64–1.57) | 0.91 (0.58–1.43) | – | Age, sex, period | 492 |
| Vasama-Neuvonen et al.8 | – | – | – | 1.3 (1.0–1.7) | – | Age, sex, period, social status | 60 |
| Czene et al.56 | 1.02 (0.95–1.09) | 1.28 (1.12–1.47) | 0.91 (0.77–1.08) | 1.11 (0.96–1.28) | – | Age, sex, period | 3901 |
H = hospital controls; P = population controls.
Study-specific RRs and 95% CIs of gynaecologic cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Breast . | Cervix uteri . | Corpus uteri . | Ovary . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | 0.91 (0.48–1.70) | 1.10 (0.51–2.24) | 1.52 (0.50–3.89) | 2.91 (1.21–6.46) | H | Age, sex | 21/719 |
| Kinlen et al.44 | 0.58 (0.06–2.77) | – | – | – | H/P | Age, sex, marital status, social class | 191/561 |
| Koenig et al.45 | 0.70 (0.14–3.44) | – | – | – | P | Age, sex, family history, age at 1st birth, others | 398/790 |
| Habel et al.46 | 1.5 (0.5–4.8) | – | – | – | P | Age, sex, education, alcohol, body mass index | 537/492 |
| Band et al.47 | 1.05 (0.46–2.41) | – | – | – | P | Age, sex, education, alcohol, smoking, others | 1018/1020 |
| Proportionate mortality or morbidity studies | |||||||
| Menck et al.48 | 1.01 (0.75–1.36) | – | – | – | – | Age, sex | 135 |
| Kono et al.49 | 0.59 (0.19–1.38) | – | – | 1.36 (0.44–3.16) | – | Age, sex, period | 141 |
| Spinelli et al.50 | 0.79 (0.36–15.1) | – | – | 2.04 (0.88–4.03) | – | Age, sex | 39 |
| Lamba et al.51 | 1.11 (1.04–1.17) | 0.96 (0.80–1.14) | 0.94 (0.80–1.10) | 1.02 (0.92–1.14) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Teta et al.52 | 1.02 (0.89–1.17) | 0.80 (0.55–1.13) | 1.23 (0.95–1.56) | 1.34 (0.99–1.78) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 0.56 (0.27–1.17) | 1.90 (0.71–5.06) | – | 0.5 (0.07–3.55) | – | Age, sex, matrimonial status | 65 |
| Kato et al.54 | 1.33 (1.00–1.78) | – | – | – | – | Age, sex | 46 |
| Andersen et al.55 (Denmark) | 1.01 (0.85–1.20) | 1.08 (0.81–1.45) | 1.52 (1.12–2.06) | 1.33 (0.97–1.83) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.03 (0.88–1.21) | 1.26 (0.79–2.00) | 1.24 (0.91–1.68) | – | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.00 (0.80–1.25) | 0.92 (0.58–1.46) | 1 (0.64–1.57) | 0.91 (0.58–1.43) | – | Age, sex, period | 492 |
| Vasama-Neuvonen et al.8 | – | – | – | 1.3 (1.0–1.7) | – | Age, sex, period, social status | 60 |
| Czene et al.56 | 1.02 (0.95–1.09) | 1.28 (1.12–1.47) | 0.91 (0.77–1.08) | 1.11 (0.96–1.28) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Breast . | Cervix uteri . | Corpus uteri . | Ovary . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | 0.91 (0.48–1.70) | 1.10 (0.51–2.24) | 1.52 (0.50–3.89) | 2.91 (1.21–6.46) | H | Age, sex | 21/719 |
| Kinlen et al.44 | 0.58 (0.06–2.77) | – | – | – | H/P | Age, sex, marital status, social class | 191/561 |
| Koenig et al.45 | 0.70 (0.14–3.44) | – | – | – | P | Age, sex, family history, age at 1st birth, others | 398/790 |
| Habel et al.46 | 1.5 (0.5–4.8) | – | – | – | P | Age, sex, education, alcohol, body mass index | 537/492 |
| Band et al.47 | 1.05 (0.46–2.41) | – | – | – | P | Age, sex, education, alcohol, smoking, others | 1018/1020 |
| Proportionate mortality or morbidity studies | |||||||
| Menck et al.48 | 1.01 (0.75–1.36) | – | – | – | – | Age, sex | 135 |
| Kono et al.49 | 0.59 (0.19–1.38) | – | – | 1.36 (0.44–3.16) | – | Age, sex, period | 141 |
| Spinelli et al.50 | 0.79 (0.36–15.1) | – | – | 2.04 (0.88–4.03) | – | Age, sex | 39 |
| Lamba et al.51 | 1.11 (1.04–1.17) | 0.96 (0.80–1.14) | 0.94 (0.80–1.10) | 1.02 (0.92–1.14) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Teta et al.52 | 1.02 (0.89–1.17) | 0.80 (0.55–1.13) | 1.23 (0.95–1.56) | 1.34 (0.99–1.78) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 0.56 (0.27–1.17) | 1.90 (0.71–5.06) | – | 0.5 (0.07–3.55) | – | Age, sex, matrimonial status | 65 |
| Kato et al.54 | 1.33 (1.00–1.78) | – | – | – | – | Age, sex | 46 |
| Andersen et al.55 (Denmark) | 1.01 (0.85–1.20) | 1.08 (0.81–1.45) | 1.52 (1.12–2.06) | 1.33 (0.97–1.83) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.03 (0.88–1.21) | 1.26 (0.79–2.00) | 1.24 (0.91–1.68) | – | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.00 (0.80–1.25) | 0.92 (0.58–1.46) | 1 (0.64–1.57) | 0.91 (0.58–1.43) | – | Age, sex, period | 492 |
| Vasama-Neuvonen et al.8 | – | – | – | 1.3 (1.0–1.7) | – | Age, sex, period, social status | 60 |
| Czene et al.56 | 1.02 (0.95–1.09) | 1.28 (1.12–1.47) | 0.91 (0.77–1.08) | 1.11 (0.96–1.28) | – | Age, sex, period | 3901 |
H = hospital controls; P = population controls.
Study-specific RRs and 95% CIs of haematopoietic cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Hodgkin's disease . | Non-Hodgkin's lymphoma . | Multiple myeloma . | Leukemia . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | – | 1.27 (0.37–3.45) | 6.41 (0.63–34.13) | 1.16 (0.03–7.78) | H | Age, sex | 139/719 |
| Flodin et al.58 | – | – | 3.3 (0.24–45.7) | – | P | Not given | 131/431 |
| Persson et al.59 | 2.7 (0.19–38.28) | 2.2 (0.17–28.71) | – | – | H | Age, sex, farming, fresh wood | 54/275 |
| Eriksson and Karlsson60 | – | – | 0.67 (0.13–3.64) | – | P | Age, sex, county | 275/275 |
| Pottern et al.61 | – | – | 0.7 (0.0–5.8) | – | P | Age, sex | 607/2596 |
| Cote et al.10 | – | 0.65 (0.3–1.3) | – | – | P | Age, sex, race | 2153/8612 |
| Blair et al.62 | – | 2.7 (0.9–8.7) | – | – | P | Age, sex, race, smoking, death year, others | 622/1245 |
| Herrinton et al.63 | – | – | 1.32 (0.65– 2.65) | – | P | Age, sex, race, location, education level | 360/933 |
| Figgs et al.64 | – | – | 1.7 (1.1–2.6) | – | P | Age, sex, race | 12 148/60 740 |
| Mele et al.65 | – | – | – | 2.25 (0.77–6.58) | H | Age, sex, region, education | 517/1161 |
| Miligi et al.66 | 2.1 (0.7–6.5) | 1.9 (0.7–5.8) | 11.1 (1.8–67.0) | 2.2 (0.7–7.1) | P | Age, sex, smoking, education | 1170/828 |
| Seniori Costantini et al.67 | – | 0.6 (0.2–1.6) | 2.2 (0.7–6.9)) | 1.0 (0.3–3.2) | P | Age, sex | 2737/1779 |
| ‘t Mannetje et al.11 | – | 1.09 (0.27–4.35) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 291/471 |
| Proportionate mortality studies | |||||||
| Alderson90 | – | – | – | 1.11 (0.36–3.44) | – | Age, sex, period | 134 |
| Kono et al.49 | – | – | – | 1.37 (0.50–2.98) | – | Age, sex, period | 141 |
| Spinelli et al.50 | – | – | 6.19 (1.27–18.11) | 1.11 (0.13–4.01) | – | Age, sex | 39 |
| Gallagher et al.93 | 0.56 (0.01–3.10) | 0.99 (0.12–3.59) | 0.58 (0.07–2.11) | 1.69 (0.94–2.78) | – | Age, sex | 288 |
| Shibata et al.68 | – | 0.78 (0.19–3.10) | – | 1.16 (0.37–3.60) | – | Age, sex | 5 |
| Lamba et al.51 | 1.38 (1.08–1.75) | 1.11 (1.01–1.24) | 1.21 (1.06–1.39) | 1.1 (1.02–1.2) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Guidotti et al.57 | – | – | 3.73 (2.53–5.51) | – | – | Age | Not given |
| Teta et al.52 | – | 1.29 (0.81–1.95) | 0.69 (0.14–2.02) | 1.20 (0.66–2.02) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | – | – | 2.5 (0.35–17.75) | – | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.20–9.94) | 1.3 (0.49–3.46) | 2.5 (0.95–6.58) | 1.1 (0.53–2.30) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.61 (0.81–3.22) | 1.54 (1.05–2.25) | 0.90 (0.45–1.89) | 0.99 (0.63–1.55) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.08 (0.35–3.35) | 0.97 (0.50–1.86) | 1.12 (0.53–2.35) | 0.99 (0.54–1.85) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | – | 1.16 (0.70–1.93) | 1.16 (0.48–2.79) | 1.41 (0.73–2.71) | – | Age, sex, period | 492 |
| Czene et al.56 | 0.78 (0.50–1.20) | 0.93 (0.76–1.14) | 1.25 (0.95–1.65) | 1.00 (0.81–1.23) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Hodgkin's disease . | Non-Hodgkin's lymphoma . | Multiple myeloma . | Leukemia . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | – | 1.27 (0.37–3.45) | 6.41 (0.63–34.13) | 1.16 (0.03–7.78) | H | Age, sex | 139/719 |
| Flodin et al.58 | – | – | 3.3 (0.24–45.7) | – | P | Not given | 131/431 |
| Persson et al.59 | 2.7 (0.19–38.28) | 2.2 (0.17–28.71) | – | – | H | Age, sex, farming, fresh wood | 54/275 |
| Eriksson and Karlsson60 | – | – | 0.67 (0.13–3.64) | – | P | Age, sex, county | 275/275 |
| Pottern et al.61 | – | – | 0.7 (0.0–5.8) | – | P | Age, sex | 607/2596 |
| Cote et al.10 | – | 0.65 (0.3–1.3) | – | – | P | Age, sex, race | 2153/8612 |
| Blair et al.62 | – | 2.7 (0.9–8.7) | – | – | P | Age, sex, race, smoking, death year, others | 622/1245 |
| Herrinton et al.63 | – | – | 1.32 (0.65– 2.65) | – | P | Age, sex, race, location, education level | 360/933 |
| Figgs et al.64 | – | – | 1.7 (1.1–2.6) | – | P | Age, sex, race | 12 148/60 740 |
| Mele et al.65 | – | – | – | 2.25 (0.77–6.58) | H | Age, sex, region, education | 517/1161 |
| Miligi et al.66 | 2.1 (0.7–6.5) | 1.9 (0.7–5.8) | 11.1 (1.8–67.0) | 2.2 (0.7–7.1) | P | Age, sex, smoking, education | 1170/828 |
| Seniori Costantini et al.67 | – | 0.6 (0.2–1.6) | 2.2 (0.7–6.9)) | 1.0 (0.3–3.2) | P | Age, sex | 2737/1779 |
| ‘t Mannetje et al.11 | – | 1.09 (0.27–4.35) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 291/471 |
| Proportionate mortality studies | |||||||
| Alderson90 | – | – | – | 1.11 (0.36–3.44) | – | Age, sex, period | 134 |
| Kono et al.49 | – | – | – | 1.37 (0.50–2.98) | – | Age, sex, period | 141 |
| Spinelli et al.50 | – | – | 6.19 (1.27–18.11) | 1.11 (0.13–4.01) | – | Age, sex | 39 |
| Gallagher et al.93 | 0.56 (0.01–3.10) | 0.99 (0.12–3.59) | 0.58 (0.07–2.11) | 1.69 (0.94–2.78) | – | Age, sex | 288 |
| Shibata et al.68 | – | 0.78 (0.19–3.10) | – | 1.16 (0.37–3.60) | – | Age, sex | 5 |
| Lamba et al.51 | 1.38 (1.08–1.75) | 1.11 (1.01–1.24) | 1.21 (1.06–1.39) | 1.1 (1.02–1.2) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Guidotti et al.57 | – | – | 3.73 (2.53–5.51) | – | – | Age | Not given |
| Teta et al.52 | – | 1.29 (0.81–1.95) | 0.69 (0.14–2.02) | 1.20 (0.66–2.02) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | – | – | 2.5 (0.35–17.75) | – | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.20–9.94) | 1.3 (0.49–3.46) | 2.5 (0.95–6.58) | 1.1 (0.53–2.30) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.61 (0.81–3.22) | 1.54 (1.05–2.25) | 0.90 (0.45–1.89) | 0.99 (0.63–1.55) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.08 (0.35–3.35) | 0.97 (0.50–1.86) | 1.12 (0.53–2.35) | 0.99 (0.54–1.85) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | – | 1.16 (0.70–1.93) | 1.16 (0.48–2.79) | 1.41 (0.73–2.71) | – | Age, sex, period | 492 |
| Czene et al.56 | 0.78 (0.50–1.20) | 0.93 (0.76–1.14) | 1.25 (0.95–1.65) | 1.00 (0.81–1.23) | – | Age, sex, period | 3901 |
H = hospital controls; P = population controls.
Study-specific RRs and 95% CIs of haematopoietic cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Hodgkin's disease . | Non-Hodgkin's lymphoma . | Multiple myeloma . | Leukemia . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | – | 1.27 (0.37–3.45) | 6.41 (0.63–34.13) | 1.16 (0.03–7.78) | H | Age, sex | 139/719 |
| Flodin et al.58 | – | – | 3.3 (0.24–45.7) | – | P | Not given | 131/431 |
| Persson et al.59 | 2.7 (0.19–38.28) | 2.2 (0.17–28.71) | – | – | H | Age, sex, farming, fresh wood | 54/275 |
| Eriksson and Karlsson60 | – | – | 0.67 (0.13–3.64) | – | P | Age, sex, county | 275/275 |
| Pottern et al.61 | – | – | 0.7 (0.0–5.8) | – | P | Age, sex | 607/2596 |
| Cote et al.10 | – | 0.65 (0.3–1.3) | – | – | P | Age, sex, race | 2153/8612 |
| Blair et al.62 | – | 2.7 (0.9–8.7) | – | – | P | Age, sex, race, smoking, death year, others | 622/1245 |
| Herrinton et al.63 | – | – | 1.32 (0.65– 2.65) | – | P | Age, sex, race, location, education level | 360/933 |
| Figgs et al.64 | – | – | 1.7 (1.1–2.6) | – | P | Age, sex, race | 12 148/60 740 |
| Mele et al.65 | – | – | – | 2.25 (0.77–6.58) | H | Age, sex, region, education | 517/1161 |
| Miligi et al.66 | 2.1 (0.7–6.5) | 1.9 (0.7–5.8) | 11.1 (1.8–67.0) | 2.2 (0.7–7.1) | P | Age, sex, smoking, education | 1170/828 |
| Seniori Costantini et al.67 | – | 0.6 (0.2–1.6) | 2.2 (0.7–6.9)) | 1.0 (0.3–3.2) | P | Age, sex | 2737/1779 |
| ‘t Mannetje et al.11 | – | 1.09 (0.27–4.35) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 291/471 |
| Proportionate mortality studies | |||||||
| Alderson90 | – | – | – | 1.11 (0.36–3.44) | – | Age, sex, period | 134 |
| Kono et al.49 | – | – | – | 1.37 (0.50–2.98) | – | Age, sex, period | 141 |
| Spinelli et al.50 | – | – | 6.19 (1.27–18.11) | 1.11 (0.13–4.01) | – | Age, sex | 39 |
| Gallagher et al.93 | 0.56 (0.01–3.10) | 0.99 (0.12–3.59) | 0.58 (0.07–2.11) | 1.69 (0.94–2.78) | – | Age, sex | 288 |
| Shibata et al.68 | – | 0.78 (0.19–3.10) | – | 1.16 (0.37–3.60) | – | Age, sex | 5 |
| Lamba et al.51 | 1.38 (1.08–1.75) | 1.11 (1.01–1.24) | 1.21 (1.06–1.39) | 1.1 (1.02–1.2) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Guidotti et al.57 | – | – | 3.73 (2.53–5.51) | – | – | Age | Not given |
| Teta et al.52 | – | 1.29 (0.81–1.95) | 0.69 (0.14–2.02) | 1.20 (0.66–2.02) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | – | – | 2.5 (0.35–17.75) | – | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.20–9.94) | 1.3 (0.49–3.46) | 2.5 (0.95–6.58) | 1.1 (0.53–2.30) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.61 (0.81–3.22) | 1.54 (1.05–2.25) | 0.90 (0.45–1.89) | 0.99 (0.63–1.55) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.08 (0.35–3.35) | 0.97 (0.50–1.86) | 1.12 (0.53–2.35) | 0.99 (0.54–1.85) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | – | 1.16 (0.70–1.93) | 1.16 (0.48–2.79) | 1.41 (0.73–2.71) | – | Age, sex, period | 492 |
| Czene et al.56 | 0.78 (0.50–1.20) | 0.93 (0.76–1.14) | 1.25 (0.95–1.65) | 1.00 (0.81–1.23) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | |||
|---|---|---|---|---|---|---|---|
| References . | Hodgkin's disease . | Non-Hodgkin's lymphoma . | Multiple myeloma . | Leukemia . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||||
| Decoufle43 | – | 1.27 (0.37–3.45) | 6.41 (0.63–34.13) | 1.16 (0.03–7.78) | H | Age, sex | 139/719 |
| Flodin et al.58 | – | – | 3.3 (0.24–45.7) | – | P | Not given | 131/431 |
| Persson et al.59 | 2.7 (0.19–38.28) | 2.2 (0.17–28.71) | – | – | H | Age, sex, farming, fresh wood | 54/275 |
| Eriksson and Karlsson60 | – | – | 0.67 (0.13–3.64) | – | P | Age, sex, county | 275/275 |
| Pottern et al.61 | – | – | 0.7 (0.0–5.8) | – | P | Age, sex | 607/2596 |
| Cote et al.10 | – | 0.65 (0.3–1.3) | – | – | P | Age, sex, race | 2153/8612 |
| Blair et al.62 | – | 2.7 (0.9–8.7) | – | – | P | Age, sex, race, smoking, death year, others | 622/1245 |
| Herrinton et al.63 | – | – | 1.32 (0.65– 2.65) | – | P | Age, sex, race, location, education level | 360/933 |
| Figgs et al.64 | – | – | 1.7 (1.1–2.6) | – | P | Age, sex, race | 12 148/60 740 |
| Mele et al.65 | – | – | – | 2.25 (0.77–6.58) | H | Age, sex, region, education | 517/1161 |
| Miligi et al.66 | 2.1 (0.7–6.5) | 1.9 (0.7–5.8) | 11.1 (1.8–67.0) | 2.2 (0.7–7.1) | P | Age, sex, smoking, education | 1170/828 |
| Seniori Costantini et al.67 | – | 0.6 (0.2–1.6) | 2.2 (0.7–6.9)) | 1.0 (0.3–3.2) | P | Age, sex | 2737/1779 |
| ‘t Mannetje et al.11 | – | 1.09 (0.27–4.35) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 291/471 |
| Proportionate mortality studies | |||||||
| Alderson90 | – | – | – | 1.11 (0.36–3.44) | – | Age, sex, period | 134 |
| Kono et al.49 | – | – | – | 1.37 (0.50–2.98) | – | Age, sex, period | 141 |
| Spinelli et al.50 | – | – | 6.19 (1.27–18.11) | 1.11 (0.13–4.01) | – | Age, sex | 39 |
| Gallagher et al.93 | 0.56 (0.01–3.10) | 0.99 (0.12–3.59) | 0.58 (0.07–2.11) | 1.69 (0.94–2.78) | – | Age, sex | 288 |
| Shibata et al.68 | – | 0.78 (0.19–3.10) | – | 1.16 (0.37–3.60) | – | Age, sex | 5 |
| Lamba et al.51 | 1.38 (1.08–1.75) | 1.11 (1.01–1.24) | 1.21 (1.06–1.39) | 1.1 (1.02–1.2) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||||
| Guidotti et al.57 | – | – | 3.73 (2.53–5.51) | – | – | Age | Not given |
| Teta et al.52 | – | 1.29 (0.81–1.95) | 0.69 (0.14–2.02) | 1.20 (0.66–2.02) | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | – | – | 2.5 (0.35–17.75) | – | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.20–9.94) | 1.3 (0.49–3.46) | 2.5 (0.95–6.58) | 1.1 (0.53–2.30) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.61 (0.81–3.22) | 1.54 (1.05–2.25) | 0.90 (0.45–1.89) | 0.99 (0.63–1.55) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.08 (0.35–3.35) | 0.97 (0.50–1.86) | 1.12 (0.53–2.35) | 0.99 (0.54–1.85) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | – | 1.16 (0.70–1.93) | 1.16 (0.48–2.79) | 1.41 (0.73–2.71) | – | Age, sex, period | 492 |
| Czene et al.56 | 0.78 (0.50–1.20) | 0.93 (0.76–1.14) | 1.25 (0.95–1.65) | 1.00 (0.81–1.23) | – | Age, sex, period | 3901 |
H = hospital controls; P = population controls.
Study-specific RRs and 95% CI of urinary tract cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | ||
|---|---|---|---|---|---|---|
| References . | Bladder . | Kidney . | Prostate . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||
| Wynder et al.69 | 5.07 (0.56–240.48) | – | – | H | Age, sex | 300/300 |
| Anthony and Thomas70 | 4.90 (0.58–222.42) | – | – | H | Age, sex, residence, smoking | 1030/741 |
| Cole et al.71 | 0.64 (0.27–1.54) | – | – | P | Age, sex | 461/485 |
| Decoufle43 | – | 1.28 (0.03–8.64) | – | H | Age, sex | 21/719 |
| Glashan and Cartwright72 | 0.9 (0.3–3.2) | – | – | H | Age, sex, year of diagnosis | 991/1338 |
| Schoenberg et al.73 | 1.27 (0.59–2.73) | – | – | P | Age, sex, smoking | 706/1392 |
| Vineis and Magnani74 | 0.9 (0.4–2.3) | – | – | H | Age, sex | 512/596 |
| Morrison et al.75 | 1.6 (0.38–6.67) | – | – | P | Age, sex, smoking | 430/397 |
| Baxter and McDowall76 | 2.0 (0.75–5.33) | – | – | P | Age, sex, borough | 54/108 |
| Risch et al.77 | 0.66 (0.19–2.23) | – | – | P | Age, sex, residence, smoking | 826/792 |
| Jensen et al.78 | – | 3.0 (0.3–33.0) | – | H | Age, sex, hospital, smoking | 96/288 |
| Silverman et al.79 | 1.3 (0.8–2.3) | – | – | P | Age, residence, smoking, education, source of drinking water | 2100/3874 |
| Silverman et al.80 | 1.4 (0.7–2.9) | – | – | P | Age, smoking, residence, education, source drinking water | 652/1266 |
| Kunze et al.81 | 1.67 (0.61–4.54) | – | – | H | Age, sex, smoking, beer intake, family history | 675/675 |
| Cordier et al.82 | 2.21 (0.41–11.94) | – | – | H | Age, sex, ethnicity, residence, smoking | 765/765 |
| Siematycki et al.83 | 1.0 (0.3–2.9) | – | – | H/P | Age, sex, ethnicity, smoking, economic status, coffee | 484/1879 |
| Teschke et al.84 | 3.2 (0.2–176) | – | – | P | Age, sex, smoking | 105/159 |
| Sorahan et al.85 | 1.75 (0.94–3.28) | – | – | P | Age, sex, smoking | 1427/2199 |
| Gago Dominguez et al.86 | 1.5 (0.7–3.2) | – | – | P | Age, sex, ethnicity, neighbourhood, smoking | 1514/1514 |
| Zheng et al.87 | 1.8 (0.4–8.0) | – | – | P | Age, sex, smoking, first-degree relative with bladder cancer | 1452/2434 |
| Gaertner et al.88 | 1.43 (0.67– 3.01) | – | – | P | Age, sex, province, smoking, diet | 887/2847 |
| Dryson et al.9 | 4.02 (1.05–15.36) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 213/471 |
| Golka et al.89 | 4.90 (0.85–28.39) | – | – | H | Age, sex, smoking | 156/336 |
| Proportionate mortality studies | ||||||
| Alderson90 | 1.25 (0.60–2.62) | – | – | – | Age, sex, calendar period | 134 |
| Dubrow and Wegman91 | 1.16 (0.43–3.08) | – | – | – | Age, sex | 4 |
| Pearce and Howard92 | 12.94 (1.45–46.7) | – | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 1.34 (0.69–2.34) | – | 1.03 (0.67–1.50) | – | Age, sex | 288 |
| Lamba et al.51 | 1.16 (1.01–1.34) | 1.02 (0.87–1.18) | 0.90 (0.81–.00) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||
| Dunham et al.94 | 2.76 (1.04–7.35) | – | – | – | Not given | 4 |
| Teta et al.52 | 1.36 (0.74–2.27) | 1.29 (0.62–2.37) | – | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 1.94 (1.13–3.34) | 1.77 (0.57–5.53) | 1.97 (1.12–3.47) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 0.7 (0.23–2.17) | 1.0 (0.25–4.00) | 1.5 (0.98–2.3) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.51 (1.21–1.89) | 1.44 (1.00–2.07) | 1.03 (0.77–1.38) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.39 (0.75–2.59) | 0.89 (0.5–1.56) | 1.56 (0.65–3.75) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.57 (1.11–2.20) | 1.23 (0.71–2.12) | 0.86 (0.60–1.23) | – | Age, sex, period | 492 |
| Czene et al.56 | 1.16 (0.96–1.39) | 1.17 (0.97–1.41) | 0.94 (0.82–1.08) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | ||
|---|---|---|---|---|---|---|
| References . | Bladder . | Kidney . | Prostate . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||
| Wynder et al.69 | 5.07 (0.56–240.48) | – | – | H | Age, sex | 300/300 |
| Anthony and Thomas70 | 4.90 (0.58–222.42) | – | – | H | Age, sex, residence, smoking | 1030/741 |
| Cole et al.71 | 0.64 (0.27–1.54) | – | – | P | Age, sex | 461/485 |
| Decoufle43 | – | 1.28 (0.03–8.64) | – | H | Age, sex | 21/719 |
| Glashan and Cartwright72 | 0.9 (0.3–3.2) | – | – | H | Age, sex, year of diagnosis | 991/1338 |
| Schoenberg et al.73 | 1.27 (0.59–2.73) | – | – | P | Age, sex, smoking | 706/1392 |
| Vineis and Magnani74 | 0.9 (0.4–2.3) | – | – | H | Age, sex | 512/596 |
| Morrison et al.75 | 1.6 (0.38–6.67) | – | – | P | Age, sex, smoking | 430/397 |
| Baxter and McDowall76 | 2.0 (0.75–5.33) | – | – | P | Age, sex, borough | 54/108 |
| Risch et al.77 | 0.66 (0.19–2.23) | – | – | P | Age, sex, residence, smoking | 826/792 |
| Jensen et al.78 | – | 3.0 (0.3–33.0) | – | H | Age, sex, hospital, smoking | 96/288 |
| Silverman et al.79 | 1.3 (0.8–2.3) | – | – | P | Age, residence, smoking, education, source of drinking water | 2100/3874 |
| Silverman et al.80 | 1.4 (0.7–2.9) | – | – | P | Age, smoking, residence, education, source drinking water | 652/1266 |
| Kunze et al.81 | 1.67 (0.61–4.54) | – | – | H | Age, sex, smoking, beer intake, family history | 675/675 |
| Cordier et al.82 | 2.21 (0.41–11.94) | – | – | H | Age, sex, ethnicity, residence, smoking | 765/765 |
| Siematycki et al.83 | 1.0 (0.3–2.9) | – | – | H/P | Age, sex, ethnicity, smoking, economic status, coffee | 484/1879 |
| Teschke et al.84 | 3.2 (0.2–176) | – | – | P | Age, sex, smoking | 105/159 |
| Sorahan et al.85 | 1.75 (0.94–3.28) | – | – | P | Age, sex, smoking | 1427/2199 |
| Gago Dominguez et al.86 | 1.5 (0.7–3.2) | – | – | P | Age, sex, ethnicity, neighbourhood, smoking | 1514/1514 |
| Zheng et al.87 | 1.8 (0.4–8.0) | – | – | P | Age, sex, smoking, first-degree relative with bladder cancer | 1452/2434 |
| Gaertner et al.88 | 1.43 (0.67– 3.01) | – | – | P | Age, sex, province, smoking, diet | 887/2847 |
| Dryson et al.9 | 4.02 (1.05–15.36) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 213/471 |
| Golka et al.89 | 4.90 (0.85–28.39) | – | – | H | Age, sex, smoking | 156/336 |
| Proportionate mortality studies | ||||||
| Alderson90 | 1.25 (0.60–2.62) | – | – | – | Age, sex, calendar period | 134 |
| Dubrow and Wegman91 | 1.16 (0.43–3.08) | – | – | – | Age, sex | 4 |
| Pearce and Howard92 | 12.94 (1.45–46.7) | – | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 1.34 (0.69–2.34) | – | 1.03 (0.67–1.50) | – | Age, sex | 288 |
| Lamba et al.51 | 1.16 (1.01–1.34) | 1.02 (0.87–1.18) | 0.90 (0.81–.00) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||
| Dunham et al.94 | 2.76 (1.04–7.35) | – | – | – | Not given | 4 |
| Teta et al.52 | 1.36 (0.74–2.27) | 1.29 (0.62–2.37) | – | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 1.94 (1.13–3.34) | 1.77 (0.57–5.53) | 1.97 (1.12–3.47) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 0.7 (0.23–2.17) | 1.0 (0.25–4.00) | 1.5 (0.98–2.3) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.51 (1.21–1.89) | 1.44 (1.00–2.07) | 1.03 (0.77–1.38) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.39 (0.75–2.59) | 0.89 (0.5–1.56) | 1.56 (0.65–3.75) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.57 (1.11–2.20) | 1.23 (0.71–2.12) | 0.86 (0.60–1.23) | – | Age, sex, period | 492 |
| Czene et al.56 | 1.16 (0.96–1.39) | 1.17 (0.97–1.41) | 0.94 (0.82–1.08) | – | Age, sex, period | 3901 |
H = hospital controls; P = population controls.
Study-specific RRs and 95% CI of urinary tract cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | ||
|---|---|---|---|---|---|---|
| References . | Bladder . | Kidney . | Prostate . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||
| Wynder et al.69 | 5.07 (0.56–240.48) | – | – | H | Age, sex | 300/300 |
| Anthony and Thomas70 | 4.90 (0.58–222.42) | – | – | H | Age, sex, residence, smoking | 1030/741 |
| Cole et al.71 | 0.64 (0.27–1.54) | – | – | P | Age, sex | 461/485 |
| Decoufle43 | – | 1.28 (0.03–8.64) | – | H | Age, sex | 21/719 |
| Glashan and Cartwright72 | 0.9 (0.3–3.2) | – | – | H | Age, sex, year of diagnosis | 991/1338 |
| Schoenberg et al.73 | 1.27 (0.59–2.73) | – | – | P | Age, sex, smoking | 706/1392 |
| Vineis and Magnani74 | 0.9 (0.4–2.3) | – | – | H | Age, sex | 512/596 |
| Morrison et al.75 | 1.6 (0.38–6.67) | – | – | P | Age, sex, smoking | 430/397 |
| Baxter and McDowall76 | 2.0 (0.75–5.33) | – | – | P | Age, sex, borough | 54/108 |
| Risch et al.77 | 0.66 (0.19–2.23) | – | – | P | Age, sex, residence, smoking | 826/792 |
| Jensen et al.78 | – | 3.0 (0.3–33.0) | – | H | Age, sex, hospital, smoking | 96/288 |
| Silverman et al.79 | 1.3 (0.8–2.3) | – | – | P | Age, residence, smoking, education, source of drinking water | 2100/3874 |
| Silverman et al.80 | 1.4 (0.7–2.9) | – | – | P | Age, smoking, residence, education, source drinking water | 652/1266 |
| Kunze et al.81 | 1.67 (0.61–4.54) | – | – | H | Age, sex, smoking, beer intake, family history | 675/675 |
| Cordier et al.82 | 2.21 (0.41–11.94) | – | – | H | Age, sex, ethnicity, residence, smoking | 765/765 |
| Siematycki et al.83 | 1.0 (0.3–2.9) | – | – | H/P | Age, sex, ethnicity, smoking, economic status, coffee | 484/1879 |
| Teschke et al.84 | 3.2 (0.2–176) | – | – | P | Age, sex, smoking | 105/159 |
| Sorahan et al.85 | 1.75 (0.94–3.28) | – | – | P | Age, sex, smoking | 1427/2199 |
| Gago Dominguez et al.86 | 1.5 (0.7–3.2) | – | – | P | Age, sex, ethnicity, neighbourhood, smoking | 1514/1514 |
| Zheng et al.87 | 1.8 (0.4–8.0) | – | – | P | Age, sex, smoking, first-degree relative with bladder cancer | 1452/2434 |
| Gaertner et al.88 | 1.43 (0.67– 3.01) | – | – | P | Age, sex, province, smoking, diet | 887/2847 |
| Dryson et al.9 | 4.02 (1.05–15.36) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 213/471 |
| Golka et al.89 | 4.90 (0.85–28.39) | – | – | H | Age, sex, smoking | 156/336 |
| Proportionate mortality studies | ||||||
| Alderson90 | 1.25 (0.60–2.62) | – | – | – | Age, sex, calendar period | 134 |
| Dubrow and Wegman91 | 1.16 (0.43–3.08) | – | – | – | Age, sex | 4 |
| Pearce and Howard92 | 12.94 (1.45–46.7) | – | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 1.34 (0.69–2.34) | – | 1.03 (0.67–1.50) | – | Age, sex | 288 |
| Lamba et al.51 | 1.16 (1.01–1.34) | 1.02 (0.87–1.18) | 0.90 (0.81–.00) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||
| Dunham et al.94 | 2.76 (1.04–7.35) | – | – | – | Not given | 4 |
| Teta et al.52 | 1.36 (0.74–2.27) | 1.29 (0.62–2.37) | – | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 1.94 (1.13–3.34) | 1.77 (0.57–5.53) | 1.97 (1.12–3.47) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 0.7 (0.23–2.17) | 1.0 (0.25–4.00) | 1.5 (0.98–2.3) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.51 (1.21–1.89) | 1.44 (1.00–2.07) | 1.03 (0.77–1.38) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.39 (0.75–2.59) | 0.89 (0.5–1.56) | 1.56 (0.65–3.75) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.57 (1.11–2.20) | 1.23 (0.71–2.12) | 0.86 (0.60–1.23) | – | Age, sex, period | 492 |
| Czene et al.56 | 1.16 (0.96–1.39) | 1.17 (0.97–1.41) | 0.94 (0.82–1.08) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | ||
|---|---|---|---|---|---|---|
| References . | Bladder . | Kidney . | Prostate . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||
| Wynder et al.69 | 5.07 (0.56–240.48) | – | – | H | Age, sex | 300/300 |
| Anthony and Thomas70 | 4.90 (0.58–222.42) | – | – | H | Age, sex, residence, smoking | 1030/741 |
| Cole et al.71 | 0.64 (0.27–1.54) | – | – | P | Age, sex | 461/485 |
| Decoufle43 | – | 1.28 (0.03–8.64) | – | H | Age, sex | 21/719 |
| Glashan and Cartwright72 | 0.9 (0.3–3.2) | – | – | H | Age, sex, year of diagnosis | 991/1338 |
| Schoenberg et al.73 | 1.27 (0.59–2.73) | – | – | P | Age, sex, smoking | 706/1392 |
| Vineis and Magnani74 | 0.9 (0.4–2.3) | – | – | H | Age, sex | 512/596 |
| Morrison et al.75 | 1.6 (0.38–6.67) | – | – | P | Age, sex, smoking | 430/397 |
| Baxter and McDowall76 | 2.0 (0.75–5.33) | – | – | P | Age, sex, borough | 54/108 |
| Risch et al.77 | 0.66 (0.19–2.23) | – | – | P | Age, sex, residence, smoking | 826/792 |
| Jensen et al.78 | – | 3.0 (0.3–33.0) | – | H | Age, sex, hospital, smoking | 96/288 |
| Silverman et al.79 | 1.3 (0.8–2.3) | – | – | P | Age, residence, smoking, education, source of drinking water | 2100/3874 |
| Silverman et al.80 | 1.4 (0.7–2.9) | – | – | P | Age, smoking, residence, education, source drinking water | 652/1266 |
| Kunze et al.81 | 1.67 (0.61–4.54) | – | – | H | Age, sex, smoking, beer intake, family history | 675/675 |
| Cordier et al.82 | 2.21 (0.41–11.94) | – | – | H | Age, sex, ethnicity, residence, smoking | 765/765 |
| Siematycki et al.83 | 1.0 (0.3–2.9) | – | – | H/P | Age, sex, ethnicity, smoking, economic status, coffee | 484/1879 |
| Teschke et al.84 | 3.2 (0.2–176) | – | – | P | Age, sex, smoking | 105/159 |
| Sorahan et al.85 | 1.75 (0.94–3.28) | – | – | P | Age, sex, smoking | 1427/2199 |
| Gago Dominguez et al.86 | 1.5 (0.7–3.2) | – | – | P | Age, sex, ethnicity, neighbourhood, smoking | 1514/1514 |
| Zheng et al.87 | 1.8 (0.4–8.0) | – | – | P | Age, sex, smoking, first-degree relative with bladder cancer | 1452/2434 |
| Gaertner et al.88 | 1.43 (0.67– 3.01) | – | – | P | Age, sex, province, smoking, diet | 887/2847 |
| Dryson et al.9 | 4.02 (1.05–15.36) | – | – | P | Age, sex, smoking, ethnicity, occupational status | 213/471 |
| Golka et al.89 | 4.90 (0.85–28.39) | – | – | H | Age, sex, smoking | 156/336 |
| Proportionate mortality studies | ||||||
| Alderson90 | 1.25 (0.60–2.62) | – | – | – | Age, sex, calendar period | 134 |
| Dubrow and Wegman91 | 1.16 (0.43–3.08) | – | – | – | Age, sex | 4 |
| Pearce and Howard92 | 12.94 (1.45–46.7) | – | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 1.34 (0.69–2.34) | – | 1.03 (0.67–1.50) | – | Age, sex | 288 |
| Lamba et al.51 | 1.16 (1.01–1.34) | 1.02 (0.87–1.18) | 0.90 (0.81–.00) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||
| Dunham et al.94 | 2.76 (1.04–7.35) | – | – | – | Not given | 4 |
| Teta et al.52 | 1.36 (0.74–2.27) | 1.29 (0.62–2.37) | – | – | Age, sex, calendar year | 688 |
| Gubéran et al.53 | 1.94 (1.13–3.34) | 1.77 (0.57–5.53) | 1.97 (1.12–3.47) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 0.7 (0.23–2.17) | 1.0 (0.25–4.00) | 1.5 (0.98–2.3) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 1.51 (1.21–1.89) | 1.44 (1.00–2.07) | 1.03 (0.77–1.38) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.39 (0.75–2.59) | 0.89 (0.5–1.56) | 1.56 (0.65–3.75) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.57 (1.11–2.20) | 1.23 (0.71–2.12) | 0.86 (0.60–1.23) | – | Age, sex, period | 492 |
| Czene et al.56 | 1.16 (0.96–1.39) | 1.17 (0.97–1.41) | 0.94 (0.82–1.08) | – | Age, sex, period | 3901 |
H = hospital controls; P = population controls.
Study-specific RRs and 95% CIs of digestive cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | ||||
|---|---|---|---|---|---|---|---|---|
| References . | Oesophagus . | Stomach . | Colon–Rectum . | Liver . | Pancreas . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||||
| Decoufle43 | – | 1.22 (0.03–8.18) | 1.02 (0.34–2.59) | – | – | H | Age, sex | 43/719 |
| Proportionate mortality or morbidity studies | ||||||||
| Menck et al.48 | – | – | 1.03 (0.58–1.81) | – | – | – | Age, sex | 135 |
| Alderson90 | 1.47 (0.61–3.53) | – | – | – | – | – | Age, sex, calendar period | 134 |
| Kono et al.49 | 0.63 (0.02–3.53) | 1.34 (1.02–1.72) | 1.69 (0.77–3.21) | 0.72 (0.29–1.48) | 0.24 (0.01–1.36) | – | Age, sex, period | 141 |
| Gallagher et al.93 | – | 1.1 (0.71–1.61) | 1.06 (0.76–1.48) | 0.70 (0.08–2.53) | 0.60 (0.27–1.15) | – | Age, sex | 288 |
| Lamba et al.51 | 0.81 (0.67–0.98) | 1.16 (1.02–1.31) | 1.05 (0.99–1.12) | 1.50 (1.36–1.64) | 1.08 (0.99–1.19) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||||
| Gubéran et al.53 | 0.91 (0.13–6.46) | 0.67 (0.22–2.09) | 1.25 (0.72–2.15) | – | 1.37 (0.44–4.24) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.35–6.00) | 1.4 (0.65–2.99) | 0.8 (0.41–1.57) | 1.2 (0.30–4.80) | 1.0 (0.42–2.40) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 0.52 (0.20–1.38) | 0.87 (0.59–1.27) | 1.11 (0.93–1.33) | 1.08 (0.49–2.40) | 0.76 (0.49–1.18) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 0.97 (0.36–2.59) | 1.03 (0.72–1.48) | 1.18 (0.89–1.57) | 1.32 (0.59–2.94) | 1.60 (1.06–2.43) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.18 (0.44–3.15) | 0.66 (0.40–1.07) | 1.09 (0.87–1.37) | 2.07 (0.67–6.42) | 1.04 (0.64–1.71) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | 1.17 (0.38–3.63) | – | – | – | – | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.20 (0.63–2.05) | 0.89 (0.73–1.09) | 1.11 (1.00–1.23) | 1.00 (0.81–1.24) | 1.30 (1.08–1.57) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | ||||
|---|---|---|---|---|---|---|---|---|
| References . | Oesophagus . | Stomach . | Colon–Rectum . | Liver . | Pancreas . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||||
| Decoufle43 | – | 1.22 (0.03–8.18) | 1.02 (0.34–2.59) | – | – | H | Age, sex | 43/719 |
| Proportionate mortality or morbidity studies | ||||||||
| Menck et al.48 | – | – | 1.03 (0.58–1.81) | – | – | – | Age, sex | 135 |
| Alderson90 | 1.47 (0.61–3.53) | – | – | – | – | – | Age, sex, calendar period | 134 |
| Kono et al.49 | 0.63 (0.02–3.53) | 1.34 (1.02–1.72) | 1.69 (0.77–3.21) | 0.72 (0.29–1.48) | 0.24 (0.01–1.36) | – | Age, sex, period | 141 |
| Gallagher et al.93 | – | 1.1 (0.71–1.61) | 1.06 (0.76–1.48) | 0.70 (0.08–2.53) | 0.60 (0.27–1.15) | – | Age, sex | 288 |
| Lamba et al.51 | 0.81 (0.67–0.98) | 1.16 (1.02–1.31) | 1.05 (0.99–1.12) | 1.50 (1.36–1.64) | 1.08 (0.99–1.19) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||||
| Gubéran et al.53 | 0.91 (0.13–6.46) | 0.67 (0.22–2.09) | 1.25 (0.72–2.15) | – | 1.37 (0.44–4.24) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.35–6.00) | 1.4 (0.65–2.99) | 0.8 (0.41–1.57) | 1.2 (0.30–4.80) | 1.0 (0.42–2.40) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 0.52 (0.20–1.38) | 0.87 (0.59–1.27) | 1.11 (0.93–1.33) | 1.08 (0.49–2.40) | 0.76 (0.49–1.18) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 0.97 (0.36–2.59) | 1.03 (0.72–1.48) | 1.18 (0.89–1.57) | 1.32 (0.59–2.94) | 1.60 (1.06–2.43) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.18 (0.44–3.15) | 0.66 (0.40–1.07) | 1.09 (0.87–1.37) | 2.07 (0.67–6.42) | 1.04 (0.64–1.71) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | 1.17 (0.38–3.63) | – | – | – | – | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.20 (0.63–2.05) | 0.89 (0.73–1.09) | 1.11 (1.00–1.23) | 1.00 (0.81–1.24) | 1.30 (1.08–1.57) | – | Age, sex, period | 3901 |
H = hospital controls.
Study-specific RRs and 95% CIs of digestive cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | ||||
|---|---|---|---|---|---|---|---|---|
| References . | Oesophagus . | Stomach . | Colon–Rectum . | Liver . | Pancreas . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||||
| Decoufle43 | – | 1.22 (0.03–8.18) | 1.02 (0.34–2.59) | – | – | H | Age, sex | 43/719 |
| Proportionate mortality or morbidity studies | ||||||||
| Menck et al.48 | – | – | 1.03 (0.58–1.81) | – | – | – | Age, sex | 135 |
| Alderson90 | 1.47 (0.61–3.53) | – | – | – | – | – | Age, sex, calendar period | 134 |
| Kono et al.49 | 0.63 (0.02–3.53) | 1.34 (1.02–1.72) | 1.69 (0.77–3.21) | 0.72 (0.29–1.48) | 0.24 (0.01–1.36) | – | Age, sex, period | 141 |
| Gallagher et al.93 | – | 1.1 (0.71–1.61) | 1.06 (0.76–1.48) | 0.70 (0.08–2.53) | 0.60 (0.27–1.15) | – | Age, sex | 288 |
| Lamba et al.51 | 0.81 (0.67–0.98) | 1.16 (1.02–1.31) | 1.05 (0.99–1.12) | 1.50 (1.36–1.64) | 1.08 (0.99–1.19) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||||
| Gubéran et al.53 | 0.91 (0.13–6.46) | 0.67 (0.22–2.09) | 1.25 (0.72–2.15) | – | 1.37 (0.44–4.24) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.35–6.00) | 1.4 (0.65–2.99) | 0.8 (0.41–1.57) | 1.2 (0.30–4.80) | 1.0 (0.42–2.40) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 0.52 (0.20–1.38) | 0.87 (0.59–1.27) | 1.11 (0.93–1.33) | 1.08 (0.49–2.40) | 0.76 (0.49–1.18) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 0.97 (0.36–2.59) | 1.03 (0.72–1.48) | 1.18 (0.89–1.57) | 1.32 (0.59–2.94) | 1.60 (1.06–2.43) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.18 (0.44–3.15) | 0.66 (0.40–1.07) | 1.09 (0.87–1.37) | 2.07 (0.67–6.42) | 1.04 (0.64–1.71) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | 1.17 (0.38–3.63) | – | – | – | – | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.20 (0.63–2.05) | 0.89 (0.73–1.09) | 1.11 (1.00–1.23) | 1.00 (0.81–1.24) | 1.30 (1.08–1.57) | – | Age, sex, period | 3901 |
| . | RR (95% CI) . | . | . | . | ||||
|---|---|---|---|---|---|---|---|---|
| References . | Oesophagus . | Stomach . | Colon–Rectum . | Liver . | Pancreas . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | ||||||||
| Decoufle43 | – | 1.22 (0.03–8.18) | 1.02 (0.34–2.59) | – | – | H | Age, sex | 43/719 |
| Proportionate mortality or morbidity studies | ||||||||
| Menck et al.48 | – | – | 1.03 (0.58–1.81) | – | – | – | Age, sex | 135 |
| Alderson90 | 1.47 (0.61–3.53) | – | – | – | – | – | Age, sex, calendar period | 134 |
| Kono et al.49 | 0.63 (0.02–3.53) | 1.34 (1.02–1.72) | 1.69 (0.77–3.21) | 0.72 (0.29–1.48) | 0.24 (0.01–1.36) | – | Age, sex, period | 141 |
| Gallagher et al.93 | – | 1.1 (0.71–1.61) | 1.06 (0.76–1.48) | 0.70 (0.08–2.53) | 0.60 (0.27–1.15) | – | Age, sex | 288 |
| Lamba et al.51 | 0.81 (0.67–0.98) | 1.16 (1.02–1.31) | 1.05 (0.99–1.12) | 1.50 (1.36–1.64) | 1.08 (0.99–1.19) | – | Age, sex, race, region | 9495 |
| Cohort studies | ||||||||
| Gubéran et al.53 | 0.91 (0.13–6.46) | 0.67 (0.22–2.09) | 1.25 (0.72–2.15) | – | 1.37 (0.44–4.24) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.4 (0.35–6.00) | 1.4 (0.65–2.99) | 0.8 (0.41–1.57) | 1.2 (0.30–4.80) | 1.0 (0.42–2.40) | – | Age, sex, calendar time, smoking | 110 |
| Andersen et al.55 (Denmark) | 0.52 (0.20–1.38) | 0.87 (0.59–1.27) | 1.11 (0.93–1.33) | 1.08 (0.49–2.40) | 0.76 (0.49–1.18) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 0.97 (0.36–2.59) | 1.03 (0.72–1.48) | 1.18 (0.89–1.57) | 1.32 (0.59–2.94) | 1.60 (1.06–2.43) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.18 (0.44–3.15) | 0.66 (0.40–1.07) | 1.09 (0.87–1.37) | 2.07 (0.67–6.42) | 1.04 (0.64–1.71) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | 1.17 (0.38–3.63) | – | – | – | – | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.20 (0.63–2.05) | 0.89 (0.73–1.09) | 1.11 (1.00–1.23) | 1.00 (0.81–1.24) | 1.30 (1.08–1.57) | – | Age, sex, period | 3901 |
H = hospital controls.
Study-specific RRs and 95% CIs of respiratory cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | |
|---|---|---|---|---|---|
| References . | Lung . | Larynx . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||
| Decoufle43 | 1.03 (0.02–6.77) | 3.20 (0.07–25.32) | H | Age, sex | 35/719 |
| Osorio et al.96 | 0.95 (0.64–1.41) | – | P | Age, sex, race, smoking | 50/56 |
| Jahn et al.97 | 1.9 (0.79–4.32) | – | P | Age, sex, smoking, region | 686/712 |
| Bofetta et al.98 | – | 2.33 (1.00–5.40) | P | Age, sex, area, smoking, alcohol | 1010/2176 |
| Proportionate mortality or morbidity studies | |||||
| Menck et al.48 | 1.76 (1.14–2.73) | – | – | Age, sex | 135 |
| Garfinkel et al.99 | 6.92 (2.87–16.72) | – | – | Age, sex, race | 25 |
| Alderson90 | 1.02 (0.78–1.34) | 0.77 (0.11–5.47) | – | Age, sex, period | 134 |
| Kono et al.49 | 1.21 (0.56–2.31) | – | – | Age, sex, period | 141 |
| Pearce and Howard92 | 2.54 (0.82–5.93) | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 0.91 (0.70–1.18) | 0.41 (0.01–2.31) | – | Age, sex | 288 |
| Lamba et al.51 | 1.13 (1.08–1.18) | 0.94 (0.71–1.25) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||
| Gubéran et al.53 | 0.99 (0.55–1.79) | 2.31 (0.75–7.16) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.6 (1.22–2.20) | 1.5 (0.21–10.65) | – | Age, sex, calendar time, smoking | 110 |
| Leigh100 | 1.38 (1.11–1.71) | – | – | Age, sex, smoking, education | 96 |
| Andersen et al.55 (Denmark) | 1.14 (0.98–1.33) | 1.05 (0.56–1.95) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.33 (0.94–1.88) | 3.05 (1.15–8.13) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.22 (0.93–1.61) | 3.2 (1.40–7.34) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | – | 1.19 (0.64–2.21) | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.36 (1.22–1.53) | – | – | Age, sex, period | 3901 |
| Ji and Hemminki101 | 1.42 (1.20–1.66) | 1.78 (1.10–2.62) | – | Age, sex, period, socio-economic status | 334 |
| . | RR (95% CI) . | . | . | . | |
|---|---|---|---|---|---|
| References . | Lung . | Larynx . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||
| Decoufle43 | 1.03 (0.02–6.77) | 3.20 (0.07–25.32) | H | Age, sex | 35/719 |
| Osorio et al.96 | 0.95 (0.64–1.41) | – | P | Age, sex, race, smoking | 50/56 |
| Jahn et al.97 | 1.9 (0.79–4.32) | – | P | Age, sex, smoking, region | 686/712 |
| Bofetta et al.98 | – | 2.33 (1.00–5.40) | P | Age, sex, area, smoking, alcohol | 1010/2176 |
| Proportionate mortality or morbidity studies | |||||
| Menck et al.48 | 1.76 (1.14–2.73) | – | – | Age, sex | 135 |
| Garfinkel et al.99 | 6.92 (2.87–16.72) | – | – | Age, sex, race | 25 |
| Alderson90 | 1.02 (0.78–1.34) | 0.77 (0.11–5.47) | – | Age, sex, period | 134 |
| Kono et al.49 | 1.21 (0.56–2.31) | – | – | Age, sex, period | 141 |
| Pearce and Howard92 | 2.54 (0.82–5.93) | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 0.91 (0.70–1.18) | 0.41 (0.01–2.31) | – | Age, sex | 288 |
| Lamba et al.51 | 1.13 (1.08–1.18) | 0.94 (0.71–1.25) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||
| Gubéran et al.53 | 0.99 (0.55–1.79) | 2.31 (0.75–7.16) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.6 (1.22–2.20) | 1.5 (0.21–10.65) | – | Age, sex, calendar time, smoking | 110 |
| Leigh100 | 1.38 (1.11–1.71) | – | – | Age, sex, smoking, education | 96 |
| Andersen et al.55 (Denmark) | 1.14 (0.98–1.33) | 1.05 (0.56–1.95) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.33 (0.94–1.88) | 3.05 (1.15–8.13) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.22 (0.93–1.61) | 3.2 (1.40–7.34) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | – | 1.19 (0.64–2.21) | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.36 (1.22–1.53) | – | – | Age, sex, period | 3901 |
| Ji and Hemminki101 | 1.42 (1.20–1.66) | 1.78 (1.10–2.62) | – | Age, sex, period, socio-economic status | 334 |
H = hospital controls; P = population controls.
Study-specific RRs and 95% CIs of respiratory cancers among hairdressers and related occupations
| . | RR (95% CI) . | . | . | . | |
|---|---|---|---|---|---|
| References . | Lung . | Larynx . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||
| Decoufle43 | 1.03 (0.02–6.77) | 3.20 (0.07–25.32) | H | Age, sex | 35/719 |
| Osorio et al.96 | 0.95 (0.64–1.41) | – | P | Age, sex, race, smoking | 50/56 |
| Jahn et al.97 | 1.9 (0.79–4.32) | – | P | Age, sex, smoking, region | 686/712 |
| Bofetta et al.98 | – | 2.33 (1.00–5.40) | P | Age, sex, area, smoking, alcohol | 1010/2176 |
| Proportionate mortality or morbidity studies | |||||
| Menck et al.48 | 1.76 (1.14–2.73) | – | – | Age, sex | 135 |
| Garfinkel et al.99 | 6.92 (2.87–16.72) | – | – | Age, sex, race | 25 |
| Alderson90 | 1.02 (0.78–1.34) | 0.77 (0.11–5.47) | – | Age, sex, period | 134 |
| Kono et al.49 | 1.21 (0.56–2.31) | – | – | Age, sex, period | 141 |
| Pearce and Howard92 | 2.54 (0.82–5.93) | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 0.91 (0.70–1.18) | 0.41 (0.01–2.31) | – | Age, sex | 288 |
| Lamba et al.51 | 1.13 (1.08–1.18) | 0.94 (0.71–1.25) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||
| Gubéran et al.53 | 0.99 (0.55–1.79) | 2.31 (0.75–7.16) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.6 (1.22–2.20) | 1.5 (0.21–10.65) | – | Age, sex, calendar time, smoking | 110 |
| Leigh100 | 1.38 (1.11–1.71) | – | – | Age, sex, smoking, education | 96 |
| Andersen et al.55 (Denmark) | 1.14 (0.98–1.33) | 1.05 (0.56–1.95) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.33 (0.94–1.88) | 3.05 (1.15–8.13) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.22 (0.93–1.61) | 3.2 (1.40–7.34) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | – | 1.19 (0.64–2.21) | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.36 (1.22–1.53) | – | – | Age, sex, period | 3901 |
| Ji and Hemminki101 | 1.42 (1.20–1.66) | 1.78 (1.10–2.62) | – | Age, sex, period, socio-economic status | 334 |
| . | RR (95% CI) . | . | . | . | |
|---|---|---|---|---|---|
| References . | Lung . | Larynx . | Type of controls . | Adjustment, matching and restriction factors . | Cases/controls or exposed cases . |
| Case–control studies | |||||
| Decoufle43 | 1.03 (0.02–6.77) | 3.20 (0.07–25.32) | H | Age, sex | 35/719 |
| Osorio et al.96 | 0.95 (0.64–1.41) | – | P | Age, sex, race, smoking | 50/56 |
| Jahn et al.97 | 1.9 (0.79–4.32) | – | P | Age, sex, smoking, region | 686/712 |
| Bofetta et al.98 | – | 2.33 (1.00–5.40) | P | Age, sex, area, smoking, alcohol | 1010/2176 |
| Proportionate mortality or morbidity studies | |||||
| Menck et al.48 | 1.76 (1.14–2.73) | – | – | Age, sex | 135 |
| Garfinkel et al.99 | 6.92 (2.87–16.72) | – | – | Age, sex, race | 25 |
| Alderson90 | 1.02 (0.78–1.34) | 0.77 (0.11–5.47) | – | Age, sex, period | 134 |
| Kono et al.49 | 1.21 (0.56–2.31) | – | – | Age, sex, period | 141 |
| Pearce and Howard92 | 2.54 (0.82–5.93) | – | – | Age, sex, social class | 7 |
| Gallagher et al.93 | 0.91 (0.70–1.18) | 0.41 (0.01–2.31) | – | Age, sex | 288 |
| Lamba et al.51 | 1.13 (1.08–1.18) | 0.94 (0.71–1.25) | – | Age, sex, race, region | 9495 |
| Cohort studies | |||||
| Gubéran et al.53 | 0.99 (0.55–1.79) | 2.31 (0.75–7.16) | – | Age, sex, matrimonial status | 65 |
| Hrubec et al.95 | 1.6 (1.22–2.20) | 1.5 (0.21–10.65) | – | Age, sex, calendar time, smoking | 110 |
| Leigh100 | 1.38 (1.11–1.71) | – | – | Age, sex, smoking, education | 96 |
| Andersen et al.55 (Denmark) | 1.14 (0.98–1.33) | 1.05 (0.56–1.95) | – | Age, sex, period | 911 |
| Andersen et al.55 (Finland) | 1.33 (0.94–1.88) | 3.05 (1.15–8.13) | – | Age, sex, period | 549 |
| Andersen et al.55 (Norway) | 1.22 (0.93–1.61) | 3.2 (1.40–7.34) | – | Age, sex, period | 492 |
| Andersen et al.55 (Sweden) | – | 1.19 (0.64–2.21) | – | Age, sex, period | 1528 |
| Czene et al.56 | 1.36 (1.22–1.53) | – | – | Age, sex, period | 3901 |
| Ji and Hemminki101 | 1.42 (1.20–1.66) | 1.78 (1.10–2.62) | – | Age, sex, period, socio-economic status | 334 |
H = hospital controls; P = population controls.
One of the most challenging tasks in this meta-analysis was to trace the same cohort in different publications and thus, to avoid including several times the same study population.
Among the studies that could have been relevant to our meta-analysis but were finally excluded, several were discarded because either they were an update of the same cohort or duplicate publications of the same results.22–36 Four studies were excluded because the corresponding CI of the effect measure was either not available,37,38 or was undefined as no case of cancer was observed among hairdressers.39,40 We also discarded two articles that presented pooled results from previously published studies, and we included the original individual studies instead.41,42 When grouped all together, the 247 studies yielded a random effects pooled RR of 1.15 (95% CI 1.12–1.19).
Gynaecologic cancers
We retrieved 41 studies on gynaecologic cancers;8,43–56 more specifically: 16 studies on breast cancer, 8 studies on cervix uteri cancer, 7 studies on corpus uteri cancer and 10 studies on ovary cancer, published between 1977 and 2003 (Table 1). Compared with other occupations, hairdressers globally present a slight increase in the risk of breast, cervix uteri and ovary, which varies between 6% for breast cancer and 12% for ovary cancer (Table 6). Except for corpus uteri cancer, heterogeneity is low, and thus, fixed and random effects pooled estimates are very similar if not identical. Stratifying the analysis by design, we found that the effect subsided among cohort studies for breast cancer. The contrary occurred in other gynaecologic cancers, for which the effect increased among cohort studies and decreased among case–control studies.
Pooled RRs and 95% CIs of gynaecologic cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Breast | |||||
| All studies | 16 | 1.06 (1.02–1.10) | 1.06 (1.02–1.10) | 0.00 | 0.54 |
| Cohort studies | 7 | 1.02 (0.97–1.08) | 1.02 (0.97–1.08) | 0.00 | 0.45 |
| Case–control studies | 9 | 1.10 (1.05–1.16) | 1.10 (1.05–1.16) | 0.00 | 0.84 |
| Incidence-only studies | 12 | 1.03 (0.98–1.08) | 1.03 (0.98–1.08) | 0.00 | 0.95 |
| Cervix uteri | |||||
| All studies | 8 | 1.11 (1.01–1.21) | 1.07 (0.92–1.25) | 0.49 | 0.09 |
| Cohort studies | 6 | 1.17 (1.05–1.31) | 1.11 (0.92–1.33) | 0.52 | 0.12 |
| Case–control studies | 2 | 0.97 (0.82–1.14) | 0.97 (0.82–1.14) | 0.00 | 0.72 |
| Incidence-only studies | 7 | 1.17 (1.05–1.31) | 1.11 (0.95–1.31) | 0.40 | 0.19 |
| Corpus uteri | |||||
| All studies | 7 | 1.05 (0.95–1.14) | 1.11 (0.95–1.29) | 0.59 | 0.03 |
| Cohort studies | 5 | 1.10 (0.98–1.23) | 1.15 (0.94–1.41) | 0.65 | 0.03 |
| Case–control studies | 2 | 0.95 (0.82–1.11) | 0.95 (0.82–1.11) | 0.00 | 0.32 |
| Incidence-only studies | 6 | 1.10 (0.99–1.239 | 1.16 (0.96–1.41) | 0.58 | 0.04 |
| Ovary | |||||
| All studies | 10 | 1.12 (1.04–1.21) | 1.20 (1.05–1.38) | 0.53 | 0.06 |
| Cohort studies | 6 | 1.17 (1.06–1.30) | 1.17 (1.06–1.30) | 0.00 | 0.45 |
| Case–control studies | 4 | 1.06 (0.95–1.18) | 1.57 (0.92–2.68) | 0.94 | 0.01 |
| Incidence-only studies | 6 | 1.20 (1.08–1.33) | 1.24 (1.06–1.46) | 0.48 | 0.12 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Breast | |||||
| All studies | 16 | 1.06 (1.02–1.10) | 1.06 (1.02–1.10) | 0.00 | 0.54 |
| Cohort studies | 7 | 1.02 (0.97–1.08) | 1.02 (0.97–1.08) | 0.00 | 0.45 |
| Case–control studies | 9 | 1.10 (1.05–1.16) | 1.10 (1.05–1.16) | 0.00 | 0.84 |
| Incidence-only studies | 12 | 1.03 (0.98–1.08) | 1.03 (0.98–1.08) | 0.00 | 0.95 |
| Cervix uteri | |||||
| All studies | 8 | 1.11 (1.01–1.21) | 1.07 (0.92–1.25) | 0.49 | 0.09 |
| Cohort studies | 6 | 1.17 (1.05–1.31) | 1.11 (0.92–1.33) | 0.52 | 0.12 |
| Case–control studies | 2 | 0.97 (0.82–1.14) | 0.97 (0.82–1.14) | 0.00 | 0.72 |
| Incidence-only studies | 7 | 1.17 (1.05–1.31) | 1.11 (0.95–1.31) | 0.40 | 0.19 |
| Corpus uteri | |||||
| All studies | 7 | 1.05 (0.95–1.14) | 1.11 (0.95–1.29) | 0.59 | 0.03 |
| Cohort studies | 5 | 1.10 (0.98–1.23) | 1.15 (0.94–1.41) | 0.65 | 0.03 |
| Case–control studies | 2 | 0.95 (0.82–1.11) | 0.95 (0.82–1.11) | 0.00 | 0.32 |
| Incidence-only studies | 6 | 1.10 (0.99–1.239 | 1.16 (0.96–1.41) | 0.58 | 0.04 |
| Ovary | |||||
| All studies | 10 | 1.12 (1.04–1.21) | 1.20 (1.05–1.38) | 0.53 | 0.06 |
| Cohort studies | 6 | 1.17 (1.06–1.30) | 1.17 (1.06–1.30) | 0.00 | 0.45 |
| Case–control studies | 4 | 1.06 (0.95–1.18) | 1.57 (0.92–2.68) | 0.94 | 0.01 |
| Incidence-only studies | 6 | 1.20 (1.08–1.33) | 1.24 (1.06–1.46) | 0.48 | 0.12 |
aProportion of total variance due to between-study variance.
Pooled RRs and 95% CIs of gynaecologic cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Breast | |||||
| All studies | 16 | 1.06 (1.02–1.10) | 1.06 (1.02–1.10) | 0.00 | 0.54 |
| Cohort studies | 7 | 1.02 (0.97–1.08) | 1.02 (0.97–1.08) | 0.00 | 0.45 |
| Case–control studies | 9 | 1.10 (1.05–1.16) | 1.10 (1.05–1.16) | 0.00 | 0.84 |
| Incidence-only studies | 12 | 1.03 (0.98–1.08) | 1.03 (0.98–1.08) | 0.00 | 0.95 |
| Cervix uteri | |||||
| All studies | 8 | 1.11 (1.01–1.21) | 1.07 (0.92–1.25) | 0.49 | 0.09 |
| Cohort studies | 6 | 1.17 (1.05–1.31) | 1.11 (0.92–1.33) | 0.52 | 0.12 |
| Case–control studies | 2 | 0.97 (0.82–1.14) | 0.97 (0.82–1.14) | 0.00 | 0.72 |
| Incidence-only studies | 7 | 1.17 (1.05–1.31) | 1.11 (0.95–1.31) | 0.40 | 0.19 |
| Corpus uteri | |||||
| All studies | 7 | 1.05 (0.95–1.14) | 1.11 (0.95–1.29) | 0.59 | 0.03 |
| Cohort studies | 5 | 1.10 (0.98–1.23) | 1.15 (0.94–1.41) | 0.65 | 0.03 |
| Case–control studies | 2 | 0.95 (0.82–1.11) | 0.95 (0.82–1.11) | 0.00 | 0.32 |
| Incidence-only studies | 6 | 1.10 (0.99–1.239 | 1.16 (0.96–1.41) | 0.58 | 0.04 |
| Ovary | |||||
| All studies | 10 | 1.12 (1.04–1.21) | 1.20 (1.05–1.38) | 0.53 | 0.06 |
| Cohort studies | 6 | 1.17 (1.06–1.30) | 1.17 (1.06–1.30) | 0.00 | 0.45 |
| Case–control studies | 4 | 1.06 (0.95–1.18) | 1.57 (0.92–2.68) | 0.94 | 0.01 |
| Incidence-only studies | 6 | 1.20 (1.08–1.33) | 1.24 (1.06–1.46) | 0.48 | 0.12 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Breast | |||||
| All studies | 16 | 1.06 (1.02–1.10) | 1.06 (1.02–1.10) | 0.00 | 0.54 |
| Cohort studies | 7 | 1.02 (0.97–1.08) | 1.02 (0.97–1.08) | 0.00 | 0.45 |
| Case–control studies | 9 | 1.10 (1.05–1.16) | 1.10 (1.05–1.16) | 0.00 | 0.84 |
| Incidence-only studies | 12 | 1.03 (0.98–1.08) | 1.03 (0.98–1.08) | 0.00 | 0.95 |
| Cervix uteri | |||||
| All studies | 8 | 1.11 (1.01–1.21) | 1.07 (0.92–1.25) | 0.49 | 0.09 |
| Cohort studies | 6 | 1.17 (1.05–1.31) | 1.11 (0.92–1.33) | 0.52 | 0.12 |
| Case–control studies | 2 | 0.97 (0.82–1.14) | 0.97 (0.82–1.14) | 0.00 | 0.72 |
| Incidence-only studies | 7 | 1.17 (1.05–1.31) | 1.11 (0.95–1.31) | 0.40 | 0.19 |
| Corpus uteri | |||||
| All studies | 7 | 1.05 (0.95–1.14) | 1.11 (0.95–1.29) | 0.59 | 0.03 |
| Cohort studies | 5 | 1.10 (0.98–1.23) | 1.15 (0.94–1.41) | 0.65 | 0.03 |
| Case–control studies | 2 | 0.95 (0.82–1.11) | 0.95 (0.82–1.11) | 0.00 | 0.32 |
| Incidence-only studies | 6 | 1.10 (0.99–1.239 | 1.16 (0.96–1.41) | 0.58 | 0.04 |
| Ovary | |||||
| All studies | 10 | 1.12 (1.04–1.21) | 1.20 (1.05–1.38) | 0.53 | 0.06 |
| Cohort studies | 6 | 1.17 (1.06–1.30) | 1.17 (1.06–1.30) | 0.00 | 0.45 |
| Case–control studies | 4 | 1.06 (0.95–1.18) | 1.57 (0.92–2.68) | 0.94 | 0.01 |
| Incidence-only studies | 6 | 1.20 (1.08–1.33) | 1.24 (1.06–1.46) | 0.48 | 0.12 |
aProportion of total variance due to between-study variance.
The 12 incidence studies of breast cancer yielded a pooled RR of 1.03 (95% CI 0.98–1.08), lower than that of the four mortality studies, the result of which was 1.10 (95% CI 1.05–1.16). For ovary cancer, the incidence studies yielded a pooled RR of 1.20 (95% CI 1.08–1.33) and mortality studies a pooled RR of 1.04 (95% CI 0.93–1.16).
Restricting the analysis to those eight studies that fulfilled three or more quality criteria slightly attenuated the risk increase for breast cancer (RR 1.02; 95% CI 0.97–1.07), but did not alter the results for other gynaecologic cancers. The stratification by each item of the quality scale did not alter the results for any of the gynaecologic cancers.
Haematopoietic cancers
Table 2 presents the specific RRs for the 59 studies that dealt with haematopoietic cancers.
When all haematopoietic cancers were analysed together, we observed a risk increase (random effects pooled RR 1.26, 95% CI 1.14–1.38), which was remarkably uniform across design and gender categories. The 39 incidence studies showed a pooled RR that was only slightly higher than the pooled estimate of the 21 studies, the outcome of which was mortality by haematopoietic cancer (RR 1.28, 95% CI 1.10–1.50 for incidence studies and RR 1.22 95% CI 1.10–1.35 for mortality studies).
Separate analyses by cancer site show an increase in the risk for every anatomic site (Table 7). The increase is low for leukaemia and non-Hodgkin's lymphoma, moderate for Hodgkin's disease, and high for multiple myeloma. Heterogeneity of the study-specific RRs was low for Hodgkin's disease, non-Hodgkin's lymphoma and leukaemia (Ri between 0 and 0.16), moderate for all haematopoietic cancers grouped together (Ri = 0.46) and high for multiple myeloma (Ri = 0.75). The results of effect and heterogeneity did not change substantially after we stratified the studies by outcome (incidence/mortality), design, or gender. For every cancer site, those studies that adjusted for smoking showed higher pooled effects and less heterogeneity than those studies with incomplete adjustment. Stratifying by other quality scale variables did not produce any change in the results.
Pooled RRs and 95% CIs of haematopoietic cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| All haematopoietic cancers | |||||
| All studies | 59 | 1.17 (1.11–1.22) | 1.26 (1.14–1.38) | 0.46 | 0.0001 |
| Cohort studies | 24 | 1.16 (1.06–1.28) | 1.23 (1.04–1.45) | 0.59 | 0.0001 |
| Case–control studies | 35 | 1.17 (1.10–1.23) | 1.26 (1.13–1.40) | 0.31 | 0.09 |
| Males only | 34 | 1.17 (1.08–1.26) | 1.30 (1.12–1.50) | 0.55 | 0.001 |
| Females only | 40 | 1.18 (1.12–1.25) | 1.26 (1.13–1.41) | 0.45 | 0.002 |
| Incidence-only studies | 39 | 1.19 (1.09–1.30) | 1.28 (1.10–1.50) | 0.49 | 0.0008 |
| Hodgkin's disease | |||||
| All studies | 8 | 1.25 (1.03–1.51) | 1.22 (0.96–1.55) | 0.16 | 0.35 |
| Cohort studies | 4 | 0.98 (0.68–1.38) | 1.00 (0.69–1.44) | 0.09 | 0.36 |
| Case–control studies | 4 | 1.39 (1.10–1.75) | 1.39 (1.10–1.75) | 0.00 | 0.60 |
| Males only | 5 | 1.30 (0.99–1.69) | 1.30 (0.99–1.69) | 0.00 | 0.81 |
| Females only | 5 | 1.18 (0.89–1.56) | 1.14 (0.69–1.87) | 0.59 | 0.08 |
| Incidence-only studies | 6 | 1.06 (0.76–1.46) | 1.09 (0.77–1.56) | 0.08 | 0.37 |
| Non-Hodgkin's lymphoma | |||||
| All studies | 16 | 1.10 (1.00–1.19) | 1.10 (1.00–1.19) | 0.00 | 0.53 |
| Cohort studies | 6 | 1.08 (0.93–1.26) | 1.13 (0.93–1.37) | 0.27 | 0.26 |
| Case–control studies | 10 | 1.10 (0.99–1.22) | 1.10 (0.99–1.22) | 0.00 | 0.57 |
| Males only | 9 | 1.04 (0.90–1.21) | 1.04 (0.90–1.21) | 0.00 | 0.69 |
| Females only | 9 | 1.14 (1.03–1.26) | 1.14 (1.03–1.27) | 0.01 | 0.42 |
| Incidence-only studies | 13 | 1.08 (0.94–1.24) | 1.11 (0.94–1.32) | 0.15 | 0.32 |
| Multiple myeloma | |||||
| All studies | 19 | 1.38 (1.25–1.54) | 1.62 (1.22–2.14) | 0.75 | 0.0001 |
| Cohort studies | 8 | 1.94 (1.62–2.32) | 1.89 (1.20–2.97) | 0.80 | 0.0001 |
| Case–control studies | 11 | 1.30 (1.15–1.48) | 1.75 (1.17–2.63) | 0.79 | 0.01 |
| Males only | 8 | 1.65 (1.39–1.96) | 1.80 (1.15–2.81) | 0.79 | 0.0002 |
| Females only | 14 | 1.35 (1.17–1.55) | 1.97 (1.32–2.93) | 0.78 | 0.0001 |
| Incidence-only studies | 13 | 1.60 (1.33–1.92) | 1.57 (1.04–2.37) | 0.72 | 0.0002 |
| Leukemia | |||||
| All studies | 16 | 1.11 (1.03–1.19) | 1.11 (1.03–1.19) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.04 (0.89–1.22) | 1.04 (0.89–1.22) | 0.00 | 0.93 |
| Case–control studies | 10 | 1.13 (1.03–1.22) | 1.13 (1.03–1.22) | 0.00 | 0.75 |
| Males only | 11 | 1.06 (0.95–1.19) | 1.11 (0.96–1.28) | 0.14 | 0.35 |
| Females only | 11 | 1.15 (1.06–1.26) | 1.15 (1.06–1.26) | 0.00 | 0.90 |
| Incidence-only studies | 10 | 1.07 (0.92–1.25) | 1.07 (0.92–1.25) | 0.00 | 0.85 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| All haematopoietic cancers | |||||
| All studies | 59 | 1.17 (1.11–1.22) | 1.26 (1.14–1.38) | 0.46 | 0.0001 |
| Cohort studies | 24 | 1.16 (1.06–1.28) | 1.23 (1.04–1.45) | 0.59 | 0.0001 |
| Case–control studies | 35 | 1.17 (1.10–1.23) | 1.26 (1.13–1.40) | 0.31 | 0.09 |
| Males only | 34 | 1.17 (1.08–1.26) | 1.30 (1.12–1.50) | 0.55 | 0.001 |
| Females only | 40 | 1.18 (1.12–1.25) | 1.26 (1.13–1.41) | 0.45 | 0.002 |
| Incidence-only studies | 39 | 1.19 (1.09–1.30) | 1.28 (1.10–1.50) | 0.49 | 0.0008 |
| Hodgkin's disease | |||||
| All studies | 8 | 1.25 (1.03–1.51) | 1.22 (0.96–1.55) | 0.16 | 0.35 |
| Cohort studies | 4 | 0.98 (0.68–1.38) | 1.00 (0.69–1.44) | 0.09 | 0.36 |
| Case–control studies | 4 | 1.39 (1.10–1.75) | 1.39 (1.10–1.75) | 0.00 | 0.60 |
| Males only | 5 | 1.30 (0.99–1.69) | 1.30 (0.99–1.69) | 0.00 | 0.81 |
| Females only | 5 | 1.18 (0.89–1.56) | 1.14 (0.69–1.87) | 0.59 | 0.08 |
| Incidence-only studies | 6 | 1.06 (0.76–1.46) | 1.09 (0.77–1.56) | 0.08 | 0.37 |
| Non-Hodgkin's lymphoma | |||||
| All studies | 16 | 1.10 (1.00–1.19) | 1.10 (1.00–1.19) | 0.00 | 0.53 |
| Cohort studies | 6 | 1.08 (0.93–1.26) | 1.13 (0.93–1.37) | 0.27 | 0.26 |
| Case–control studies | 10 | 1.10 (0.99–1.22) | 1.10 (0.99–1.22) | 0.00 | 0.57 |
| Males only | 9 | 1.04 (0.90–1.21) | 1.04 (0.90–1.21) | 0.00 | 0.69 |
| Females only | 9 | 1.14 (1.03–1.26) | 1.14 (1.03–1.27) | 0.01 | 0.42 |
| Incidence-only studies | 13 | 1.08 (0.94–1.24) | 1.11 (0.94–1.32) | 0.15 | 0.32 |
| Multiple myeloma | |||||
| All studies | 19 | 1.38 (1.25–1.54) | 1.62 (1.22–2.14) | 0.75 | 0.0001 |
| Cohort studies | 8 | 1.94 (1.62–2.32) | 1.89 (1.20–2.97) | 0.80 | 0.0001 |
| Case–control studies | 11 | 1.30 (1.15–1.48) | 1.75 (1.17–2.63) | 0.79 | 0.01 |
| Males only | 8 | 1.65 (1.39–1.96) | 1.80 (1.15–2.81) | 0.79 | 0.0002 |
| Females only | 14 | 1.35 (1.17–1.55) | 1.97 (1.32–2.93) | 0.78 | 0.0001 |
| Incidence-only studies | 13 | 1.60 (1.33–1.92) | 1.57 (1.04–2.37) | 0.72 | 0.0002 |
| Leukemia | |||||
| All studies | 16 | 1.11 (1.03–1.19) | 1.11 (1.03–1.19) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.04 (0.89–1.22) | 1.04 (0.89–1.22) | 0.00 | 0.93 |
| Case–control studies | 10 | 1.13 (1.03–1.22) | 1.13 (1.03–1.22) | 0.00 | 0.75 |
| Males only | 11 | 1.06 (0.95–1.19) | 1.11 (0.96–1.28) | 0.14 | 0.35 |
| Females only | 11 | 1.15 (1.06–1.26) | 1.15 (1.06–1.26) | 0.00 | 0.90 |
| Incidence-only studies | 10 | 1.07 (0.92–1.25) | 1.07 (0.92–1.25) | 0.00 | 0.85 |
aProportion of total variance due to between-study variance.
Pooled RRs and 95% CIs of haematopoietic cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| All haematopoietic cancers | |||||
| All studies | 59 | 1.17 (1.11–1.22) | 1.26 (1.14–1.38) | 0.46 | 0.0001 |
| Cohort studies | 24 | 1.16 (1.06–1.28) | 1.23 (1.04–1.45) | 0.59 | 0.0001 |
| Case–control studies | 35 | 1.17 (1.10–1.23) | 1.26 (1.13–1.40) | 0.31 | 0.09 |
| Males only | 34 | 1.17 (1.08–1.26) | 1.30 (1.12–1.50) | 0.55 | 0.001 |
| Females only | 40 | 1.18 (1.12–1.25) | 1.26 (1.13–1.41) | 0.45 | 0.002 |
| Incidence-only studies | 39 | 1.19 (1.09–1.30) | 1.28 (1.10–1.50) | 0.49 | 0.0008 |
| Hodgkin's disease | |||||
| All studies | 8 | 1.25 (1.03–1.51) | 1.22 (0.96–1.55) | 0.16 | 0.35 |
| Cohort studies | 4 | 0.98 (0.68–1.38) | 1.00 (0.69–1.44) | 0.09 | 0.36 |
| Case–control studies | 4 | 1.39 (1.10–1.75) | 1.39 (1.10–1.75) | 0.00 | 0.60 |
| Males only | 5 | 1.30 (0.99–1.69) | 1.30 (0.99–1.69) | 0.00 | 0.81 |
| Females only | 5 | 1.18 (0.89–1.56) | 1.14 (0.69–1.87) | 0.59 | 0.08 |
| Incidence-only studies | 6 | 1.06 (0.76–1.46) | 1.09 (0.77–1.56) | 0.08 | 0.37 |
| Non-Hodgkin's lymphoma | |||||
| All studies | 16 | 1.10 (1.00–1.19) | 1.10 (1.00–1.19) | 0.00 | 0.53 |
| Cohort studies | 6 | 1.08 (0.93–1.26) | 1.13 (0.93–1.37) | 0.27 | 0.26 |
| Case–control studies | 10 | 1.10 (0.99–1.22) | 1.10 (0.99–1.22) | 0.00 | 0.57 |
| Males only | 9 | 1.04 (0.90–1.21) | 1.04 (0.90–1.21) | 0.00 | 0.69 |
| Females only | 9 | 1.14 (1.03–1.26) | 1.14 (1.03–1.27) | 0.01 | 0.42 |
| Incidence-only studies | 13 | 1.08 (0.94–1.24) | 1.11 (0.94–1.32) | 0.15 | 0.32 |
| Multiple myeloma | |||||
| All studies | 19 | 1.38 (1.25–1.54) | 1.62 (1.22–2.14) | 0.75 | 0.0001 |
| Cohort studies | 8 | 1.94 (1.62–2.32) | 1.89 (1.20–2.97) | 0.80 | 0.0001 |
| Case–control studies | 11 | 1.30 (1.15–1.48) | 1.75 (1.17–2.63) | 0.79 | 0.01 |
| Males only | 8 | 1.65 (1.39–1.96) | 1.80 (1.15–2.81) | 0.79 | 0.0002 |
| Females only | 14 | 1.35 (1.17–1.55) | 1.97 (1.32–2.93) | 0.78 | 0.0001 |
| Incidence-only studies | 13 | 1.60 (1.33–1.92) | 1.57 (1.04–2.37) | 0.72 | 0.0002 |
| Leukemia | |||||
| All studies | 16 | 1.11 (1.03–1.19) | 1.11 (1.03–1.19) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.04 (0.89–1.22) | 1.04 (0.89–1.22) | 0.00 | 0.93 |
| Case–control studies | 10 | 1.13 (1.03–1.22) | 1.13 (1.03–1.22) | 0.00 | 0.75 |
| Males only | 11 | 1.06 (0.95–1.19) | 1.11 (0.96–1.28) | 0.14 | 0.35 |
| Females only | 11 | 1.15 (1.06–1.26) | 1.15 (1.06–1.26) | 0.00 | 0.90 |
| Incidence-only studies | 10 | 1.07 (0.92–1.25) | 1.07 (0.92–1.25) | 0.00 | 0.85 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| All haematopoietic cancers | |||||
| All studies | 59 | 1.17 (1.11–1.22) | 1.26 (1.14–1.38) | 0.46 | 0.0001 |
| Cohort studies | 24 | 1.16 (1.06–1.28) | 1.23 (1.04–1.45) | 0.59 | 0.0001 |
| Case–control studies | 35 | 1.17 (1.10–1.23) | 1.26 (1.13–1.40) | 0.31 | 0.09 |
| Males only | 34 | 1.17 (1.08–1.26) | 1.30 (1.12–1.50) | 0.55 | 0.001 |
| Females only | 40 | 1.18 (1.12–1.25) | 1.26 (1.13–1.41) | 0.45 | 0.002 |
| Incidence-only studies | 39 | 1.19 (1.09–1.30) | 1.28 (1.10–1.50) | 0.49 | 0.0008 |
| Hodgkin's disease | |||||
| All studies | 8 | 1.25 (1.03–1.51) | 1.22 (0.96–1.55) | 0.16 | 0.35 |
| Cohort studies | 4 | 0.98 (0.68–1.38) | 1.00 (0.69–1.44) | 0.09 | 0.36 |
| Case–control studies | 4 | 1.39 (1.10–1.75) | 1.39 (1.10–1.75) | 0.00 | 0.60 |
| Males only | 5 | 1.30 (0.99–1.69) | 1.30 (0.99–1.69) | 0.00 | 0.81 |
| Females only | 5 | 1.18 (0.89–1.56) | 1.14 (0.69–1.87) | 0.59 | 0.08 |
| Incidence-only studies | 6 | 1.06 (0.76–1.46) | 1.09 (0.77–1.56) | 0.08 | 0.37 |
| Non-Hodgkin's lymphoma | |||||
| All studies | 16 | 1.10 (1.00–1.19) | 1.10 (1.00–1.19) | 0.00 | 0.53 |
| Cohort studies | 6 | 1.08 (0.93–1.26) | 1.13 (0.93–1.37) | 0.27 | 0.26 |
| Case–control studies | 10 | 1.10 (0.99–1.22) | 1.10 (0.99–1.22) | 0.00 | 0.57 |
| Males only | 9 | 1.04 (0.90–1.21) | 1.04 (0.90–1.21) | 0.00 | 0.69 |
| Females only | 9 | 1.14 (1.03–1.26) | 1.14 (1.03–1.27) | 0.01 | 0.42 |
| Incidence-only studies | 13 | 1.08 (0.94–1.24) | 1.11 (0.94–1.32) | 0.15 | 0.32 |
| Multiple myeloma | |||||
| All studies | 19 | 1.38 (1.25–1.54) | 1.62 (1.22–2.14) | 0.75 | 0.0001 |
| Cohort studies | 8 | 1.94 (1.62–2.32) | 1.89 (1.20–2.97) | 0.80 | 0.0001 |
| Case–control studies | 11 | 1.30 (1.15–1.48) | 1.75 (1.17–2.63) | 0.79 | 0.01 |
| Males only | 8 | 1.65 (1.39–1.96) | 1.80 (1.15–2.81) | 0.79 | 0.0002 |
| Females only | 14 | 1.35 (1.17–1.55) | 1.97 (1.32–2.93) | 0.78 | 0.0001 |
| Incidence-only studies | 13 | 1.60 (1.33–1.92) | 1.57 (1.04–2.37) | 0.72 | 0.0002 |
| Leukemia | |||||
| All studies | 16 | 1.11 (1.03–1.19) | 1.11 (1.03–1.19) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.04 (0.89–1.22) | 1.04 (0.89–1.22) | 0.00 | 0.93 |
| Case–control studies | 10 | 1.13 (1.03–1.22) | 1.13 (1.03–1.22) | 0.00 | 0.75 |
| Males only | 11 | 1.06 (0.95–1.19) | 1.11 (0.96–1.28) | 0.14 | 0.35 |
| Females only | 11 | 1.15 (1.06–1.26) | 1.15 (1.06–1.26) | 0.00 | 0.90 |
| Incidence-only studies | 10 | 1.07 (0.92–1.25) | 1.07 (0.92–1.25) | 0.00 | 0.85 |
aProportion of total variance due to between-study variance.
Urinary tract cancers
We retrieved 52 studies on urinary tract tumours: 34 on bladder, 10 on kidney and 8 on prostate (Table 3). The 34 bladder cancer studies showed a substantial increase in the risk (RR 1.30, 95% CI 1.20–1.42) (Table 8). Cohort studies, mortality studies and studies adjusted for smoking yielded a higher pooled RR. Other variables of the quality scale did not exert any impact on the results. Heterogeneity of the study-specific RRs was low (Ri = 0.16), a characteristic that was also found in the analysis of the 10 studies on kidney cancer. For this site, the pooled RR was 1.11 (1.00–1.23). The pooled RR of the eight studies on prostate cancer did not show any effect (RR 1.02, 95% CI 0.89–1.18).
Four studies provided data on hairdressers employed for >10 years. They showed a risk increase that was higher than that corresponding to ‘ever employment’. No data were available on employment for <10 years.
For kidney and prostate cancer, we did not observe any meaningful change in the results after stratification by any of the variables of the quality scale.
Digestive cancers
We retrieved 48 studies on digestive tumours43,48,49,51,53,55,56,90,93,95 (10 on oesophagus, 10 on stomach, 11 on colon, 8 on liver and 9 on pancreas) (Tables 4 and 9). We observed an increase in the risk of colon cancer, which persisted after stratification by design, outcome measure (incidence/mortality), gender and quality variables. An increase in the risk was also observed for pancreas cancer, particularly for cohort studies (RR 1.22, 95% CI 1.22–1.42). For liver cancer, we observed an increased risk for male hairdressers.
Pooled RRs and 95% CIs of urinary tract cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Bladder | |||||
| All studies | 34 | 1.30 (1.20–1.42) | 1.36 (1.22–1.52) | 0.16 | 0.24 |
| Cohort studies | 8 | 1.36 (1.21–1.53) | 1.41 (1.20–1.65) | 0.30 | 0.22 |
| Case–control studies | 26 | 1.25 (1.12–1.41) | 1.35 (1.14–1.59) | 0.16 | 0.32 |
| Males only | 26 | 1.33 (1.20–1.47) | 1.45 (1.21–1.72) | 0.45 | 0.01 |
| Females only | 10 | 1.21 (1.04–1.39) | 1.21 (1.04–1.39) | 0.00 | 0.84 |
| Smoking adjusted | 19 | 1.33 (1.07–1.67) | 1.33 (1.07–1.67) | 0.00 | 0.77 |
| Smoking non-adjusted | 15 | 1.30 (1.19–1.42) | 1.42 (1.22–1.66) | 0.49 | 0.03 |
| Incidence-only studies | 26 | 1.35 (1.21–1.50) | 1.35 (1.21–1.50) | 0.00 | 0.78 |
| Mortality-only studies | 8 | 1.24 (1.09–1.41) | 1.53 (1.06–2.20) | 0.80 | 0.009 |
| Employment >10 years | 4 | 1.89 (0.98–3.66) | 1.93 (0.94–3.97) | 0.16 | 0.32 |
| Kidney | |||||
| All studies | 10 | 1.11 (1.00–1.23) | 1.11 (1.00–1.23) | 0.00 | 0.75 |
| Cohort studies | 7 | 1.20 (1.04–1.39) | 1.20 (1.04–1.39) | 0.00 | 0.84 |
| Case–control studies | 3 | 1.03 (0.89–1.19) | 1.03 (0.89–1.19) | 0.00 | 0.66 |
| Males only | 7 | 1.08 (0.92–1.28) | 1.08 (0.92–1.28) | 0.00 | 0.48 |
| Females only | 9 | 1.13 (0.99–1.30) | 1.13 (0.99–1.30) | 0.00 | 0.75 |
| Incidence-only studies | 7 | 1.20 (1.04–1.40) | 1.20 (1.04–1.40) | 0.00 | 0.81 |
| Prostate | |||||
| All studies | 8 | 0.95 (0.89–1.03) | 1.02 (0.89–1.18) | 0.57 | 0.05 |
| Cohort studies | 6 | 1.01 (0.90–1.13) | 1.12 (0.90–1.40) | 0.66 | 0.04 |
| Case–control studies | 2 | 0.91 (0.82–1.01) | 0.91 (0.82–1.01) | 0.00 | 0.49 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Bladder | |||||
| All studies | 34 | 1.30 (1.20–1.42) | 1.36 (1.22–1.52) | 0.16 | 0.24 |
| Cohort studies | 8 | 1.36 (1.21–1.53) | 1.41 (1.20–1.65) | 0.30 | 0.22 |
| Case–control studies | 26 | 1.25 (1.12–1.41) | 1.35 (1.14–1.59) | 0.16 | 0.32 |
| Males only | 26 | 1.33 (1.20–1.47) | 1.45 (1.21–1.72) | 0.45 | 0.01 |
| Females only | 10 | 1.21 (1.04–1.39) | 1.21 (1.04–1.39) | 0.00 | 0.84 |
| Smoking adjusted | 19 | 1.33 (1.07–1.67) | 1.33 (1.07–1.67) | 0.00 | 0.77 |
| Smoking non-adjusted | 15 | 1.30 (1.19–1.42) | 1.42 (1.22–1.66) | 0.49 | 0.03 |
| Incidence-only studies | 26 | 1.35 (1.21–1.50) | 1.35 (1.21–1.50) | 0.00 | 0.78 |
| Mortality-only studies | 8 | 1.24 (1.09–1.41) | 1.53 (1.06–2.20) | 0.80 | 0.009 |
| Employment >10 years | 4 | 1.89 (0.98–3.66) | 1.93 (0.94–3.97) | 0.16 | 0.32 |
| Kidney | |||||
| All studies | 10 | 1.11 (1.00–1.23) | 1.11 (1.00–1.23) | 0.00 | 0.75 |
| Cohort studies | 7 | 1.20 (1.04–1.39) | 1.20 (1.04–1.39) | 0.00 | 0.84 |
| Case–control studies | 3 | 1.03 (0.89–1.19) | 1.03 (0.89–1.19) | 0.00 | 0.66 |
| Males only | 7 | 1.08 (0.92–1.28) | 1.08 (0.92–1.28) | 0.00 | 0.48 |
| Females only | 9 | 1.13 (0.99–1.30) | 1.13 (0.99–1.30) | 0.00 | 0.75 |
| Incidence-only studies | 7 | 1.20 (1.04–1.40) | 1.20 (1.04–1.40) | 0.00 | 0.81 |
| Prostate | |||||
| All studies | 8 | 0.95 (0.89–1.03) | 1.02 (0.89–1.18) | 0.57 | 0.05 |
| Cohort studies | 6 | 1.01 (0.90–1.13) | 1.12 (0.90–1.40) | 0.66 | 0.04 |
| Case–control studies | 2 | 0.91 (0.82–1.01) | 0.91 (0.82–1.01) | 0.00 | 0.49 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
aProportion of total variance due to between-study variance.
Pooled RRs and 95% CIs of urinary tract cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Bladder | |||||
| All studies | 34 | 1.30 (1.20–1.42) | 1.36 (1.22–1.52) | 0.16 | 0.24 |
| Cohort studies | 8 | 1.36 (1.21–1.53) | 1.41 (1.20–1.65) | 0.30 | 0.22 |
| Case–control studies | 26 | 1.25 (1.12–1.41) | 1.35 (1.14–1.59) | 0.16 | 0.32 |
| Males only | 26 | 1.33 (1.20–1.47) | 1.45 (1.21–1.72) | 0.45 | 0.01 |
| Females only | 10 | 1.21 (1.04–1.39) | 1.21 (1.04–1.39) | 0.00 | 0.84 |
| Smoking adjusted | 19 | 1.33 (1.07–1.67) | 1.33 (1.07–1.67) | 0.00 | 0.77 |
| Smoking non-adjusted | 15 | 1.30 (1.19–1.42) | 1.42 (1.22–1.66) | 0.49 | 0.03 |
| Incidence-only studies | 26 | 1.35 (1.21–1.50) | 1.35 (1.21–1.50) | 0.00 | 0.78 |
| Mortality-only studies | 8 | 1.24 (1.09–1.41) | 1.53 (1.06–2.20) | 0.80 | 0.009 |
| Employment >10 years | 4 | 1.89 (0.98–3.66) | 1.93 (0.94–3.97) | 0.16 | 0.32 |
| Kidney | |||||
| All studies | 10 | 1.11 (1.00–1.23) | 1.11 (1.00–1.23) | 0.00 | 0.75 |
| Cohort studies | 7 | 1.20 (1.04–1.39) | 1.20 (1.04–1.39) | 0.00 | 0.84 |
| Case–control studies | 3 | 1.03 (0.89–1.19) | 1.03 (0.89–1.19) | 0.00 | 0.66 |
| Males only | 7 | 1.08 (0.92–1.28) | 1.08 (0.92–1.28) | 0.00 | 0.48 |
| Females only | 9 | 1.13 (0.99–1.30) | 1.13 (0.99–1.30) | 0.00 | 0.75 |
| Incidence-only studies | 7 | 1.20 (1.04–1.40) | 1.20 (1.04–1.40) | 0.00 | 0.81 |
| Prostate | |||||
| All studies | 8 | 0.95 (0.89–1.03) | 1.02 (0.89–1.18) | 0.57 | 0.05 |
| Cohort studies | 6 | 1.01 (0.90–1.13) | 1.12 (0.90–1.40) | 0.66 | 0.04 |
| Case–control studies | 2 | 0.91 (0.82–1.01) | 0.91 (0.82–1.01) | 0.00 | 0.49 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Bladder | |||||
| All studies | 34 | 1.30 (1.20–1.42) | 1.36 (1.22–1.52) | 0.16 | 0.24 |
| Cohort studies | 8 | 1.36 (1.21–1.53) | 1.41 (1.20–1.65) | 0.30 | 0.22 |
| Case–control studies | 26 | 1.25 (1.12–1.41) | 1.35 (1.14–1.59) | 0.16 | 0.32 |
| Males only | 26 | 1.33 (1.20–1.47) | 1.45 (1.21–1.72) | 0.45 | 0.01 |
| Females only | 10 | 1.21 (1.04–1.39) | 1.21 (1.04–1.39) | 0.00 | 0.84 |
| Smoking adjusted | 19 | 1.33 (1.07–1.67) | 1.33 (1.07–1.67) | 0.00 | 0.77 |
| Smoking non-adjusted | 15 | 1.30 (1.19–1.42) | 1.42 (1.22–1.66) | 0.49 | 0.03 |
| Incidence-only studies | 26 | 1.35 (1.21–1.50) | 1.35 (1.21–1.50) | 0.00 | 0.78 |
| Mortality-only studies | 8 | 1.24 (1.09–1.41) | 1.53 (1.06–2.20) | 0.80 | 0.009 |
| Employment >10 years | 4 | 1.89 (0.98–3.66) | 1.93 (0.94–3.97) | 0.16 | 0.32 |
| Kidney | |||||
| All studies | 10 | 1.11 (1.00–1.23) | 1.11 (1.00–1.23) | 0.00 | 0.75 |
| Cohort studies | 7 | 1.20 (1.04–1.39) | 1.20 (1.04–1.39) | 0.00 | 0.84 |
| Case–control studies | 3 | 1.03 (0.89–1.19) | 1.03 (0.89–1.19) | 0.00 | 0.66 |
| Males only | 7 | 1.08 (0.92–1.28) | 1.08 (0.92–1.28) | 0.00 | 0.48 |
| Females only | 9 | 1.13 (0.99–1.30) | 1.13 (0.99–1.30) | 0.00 | 0.75 |
| Incidence-only studies | 7 | 1.20 (1.04–1.40) | 1.20 (1.04–1.40) | 0.00 | 0.81 |
| Prostate | |||||
| All studies | 8 | 0.95 (0.89–1.03) | 1.02 (0.89–1.18) | 0.57 | 0.05 |
| Cohort studies | 6 | 1.01 (0.90–1.13) | 1.12 (0.90–1.40) | 0.66 | 0.04 |
| Case–control studies | 2 | 0.91 (0.82–1.01) | 0.91 (0.82–1.01) | 0.00 | 0.49 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
aProportion of total variance due to between-study variance.
Pooled RRs and 95% CIs of digestive cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Oesophagus | |||||
| All studies | 10 | 0.87 (0.74–1.03) | 0.87 (0.74–1.03) | 0.00 | 0.78 |
| Cohort studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Case–control studies | 3 | 0.83 (0.69–1.00) | 0.83 (0.69–1.00) | 0.00 | 0.41 |
| Males only | 8 | 0.90 (0.73–1.10) | 0.90 (0.73–1.10) | 0.00 | 0.46 |
| Females only | 6 | 0.84 (0.65–1.09) | 0.84 (0.65–1.09) | 0.00 | 0.98 |
| Incidence-only studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Stomach | |||||
| All studies | 10 | 1.08 (0.99–1.18) | 1.04 (0.91–1.19) | 0.42 | 0.10 |
| Cohort studies | 6 | 0.89 (0.77–1.04) | 0.89 (0.77–1.04) | 0.00 | 0.59 |
| Case–control studies | 4 | 1.19 (1.07–1.32) | 1.19 (1.07–1.32) | 0.00 | 0.76 |
| Males only | 8 | 1.02 (0.90–1.17) | 1.02 (0.90–1.17) | 0.00 | 0.64 |
| Females only | 8 | 1.11 (1.00–1.25) | 1.06 (0.89–1.26) | 0.41 | 0.15 |
| Incidence-only studies | 7 | 0.90 (0.77–1.04) | 0.90 (0.77–1.04) | 0.00 | 0.70 |
| Colon | |||||
| All studies | 11 | 1.08 (1.02–1.13) | 1.08 (1.02–1.13) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.94 |
| Case–control studies | 5 | 1.05 (0.99–1.12) | 1.05 (0.99–1.12) | 0.00 | 0.71 |
| Males only | 8 | 1.04 (0.96–1.12) | 1.07 (0.95–1.22) | 0.43 | 0.14 |
| Females only | 9 | 1.10 (1.03–1.16) | 1.10 (1.03–1.16) | 0.00 | 0.83 |
| Incidence-only studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.99 |
| Liver | |||||
| All studies | 8 | 1.39 (1.29–1.51) | 1.17 (0.90–1.53) | 0.80 | 0.02 |
| Cohort studies | 5 | 1.05 (0.86–1.27) | 1.05 (0.86–1.27) | 0.00 | 0.76 |
| Case–control studies | 3 | 1.48 (1.35–1.61) | 1.07 (0.59–1.94) | 0.97 | 0.08 |
| Males only | 7 | 1.49 (1.37–1.63) | 1.49 (1.37–1.63) | 0.00 | 0.50 |
| Females only | 4 | 0.96 (0.78–1.17) | 0.96 (0.78–1.17) | 0.00 | 0.81 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
| Pancreas | |||||
| All studies | 9 | 1.11 (1.02–1.20) | 1.08 (0.90–1.29) | 0.63 | 0.05 |
| Cohort studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
| Case–control studies | 3 | 1.06 (0.96–1.17) | 0.75 (0.40–1.41) | 0.96 | 0.06 |
| Males only | 8 | 0.91 (0.80–1.04) | 1.06 (0.74–1.52) | 0.81 | 0.001 |
| Females only | 8 | 1.20 (1.09–1.32) | 1.20 (1.09–1.32) | 0.00 | 0.65 |
| Incidence-only studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Oesophagus | |||||
| All studies | 10 | 0.87 (0.74–1.03) | 0.87 (0.74–1.03) | 0.00 | 0.78 |
| Cohort studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Case–control studies | 3 | 0.83 (0.69–1.00) | 0.83 (0.69–1.00) | 0.00 | 0.41 |
| Males only | 8 | 0.90 (0.73–1.10) | 0.90 (0.73–1.10) | 0.00 | 0.46 |
| Females only | 6 | 0.84 (0.65–1.09) | 0.84 (0.65–1.09) | 0.00 | 0.98 |
| Incidence-only studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Stomach | |||||
| All studies | 10 | 1.08 (0.99–1.18) | 1.04 (0.91–1.19) | 0.42 | 0.10 |
| Cohort studies | 6 | 0.89 (0.77–1.04) | 0.89 (0.77–1.04) | 0.00 | 0.59 |
| Case–control studies | 4 | 1.19 (1.07–1.32) | 1.19 (1.07–1.32) | 0.00 | 0.76 |
| Males only | 8 | 1.02 (0.90–1.17) | 1.02 (0.90–1.17) | 0.00 | 0.64 |
| Females only | 8 | 1.11 (1.00–1.25) | 1.06 (0.89–1.26) | 0.41 | 0.15 |
| Incidence-only studies | 7 | 0.90 (0.77–1.04) | 0.90 (0.77–1.04) | 0.00 | 0.70 |
| Colon | |||||
| All studies | 11 | 1.08 (1.02–1.13) | 1.08 (1.02–1.13) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.94 |
| Case–control studies | 5 | 1.05 (0.99–1.12) | 1.05 (0.99–1.12) | 0.00 | 0.71 |
| Males only | 8 | 1.04 (0.96–1.12) | 1.07 (0.95–1.22) | 0.43 | 0.14 |
| Females only | 9 | 1.10 (1.03–1.16) | 1.10 (1.03–1.16) | 0.00 | 0.83 |
| Incidence-only studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.99 |
| Liver | |||||
| All studies | 8 | 1.39 (1.29–1.51) | 1.17 (0.90–1.53) | 0.80 | 0.02 |
| Cohort studies | 5 | 1.05 (0.86–1.27) | 1.05 (0.86–1.27) | 0.00 | 0.76 |
| Case–control studies | 3 | 1.48 (1.35–1.61) | 1.07 (0.59–1.94) | 0.97 | 0.08 |
| Males only | 7 | 1.49 (1.37–1.63) | 1.49 (1.37–1.63) | 0.00 | 0.50 |
| Females only | 4 | 0.96 (0.78–1.17) | 0.96 (0.78–1.17) | 0.00 | 0.81 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
| Pancreas | |||||
| All studies | 9 | 1.11 (1.02–1.20) | 1.08 (0.90–1.29) | 0.63 | 0.05 |
| Cohort studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
| Case–control studies | 3 | 1.06 (0.96–1.17) | 0.75 (0.40–1.41) | 0.96 | 0.06 |
| Males only | 8 | 0.91 (0.80–1.04) | 1.06 (0.74–1.52) | 0.81 | 0.001 |
| Females only | 8 | 1.20 (1.09–1.32) | 1.20 (1.09–1.32) | 0.00 | 0.65 |
| Incidence-only studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
aProportion of total variance due to between-study variance.
Pooled RRs and 95% CIs of digestive cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Oesophagus | |||||
| All studies | 10 | 0.87 (0.74–1.03) | 0.87 (0.74–1.03) | 0.00 | 0.78 |
| Cohort studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Case–control studies | 3 | 0.83 (0.69–1.00) | 0.83 (0.69–1.00) | 0.00 | 0.41 |
| Males only | 8 | 0.90 (0.73–1.10) | 0.90 (0.73–1.10) | 0.00 | 0.46 |
| Females only | 6 | 0.84 (0.65–1.09) | 0.84 (0.65–1.09) | 0.00 | 0.98 |
| Incidence-only studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Stomach | |||||
| All studies | 10 | 1.08 (0.99–1.18) | 1.04 (0.91–1.19) | 0.42 | 0.10 |
| Cohort studies | 6 | 0.89 (0.77–1.04) | 0.89 (0.77–1.04) | 0.00 | 0.59 |
| Case–control studies | 4 | 1.19 (1.07–1.32) | 1.19 (1.07–1.32) | 0.00 | 0.76 |
| Males only | 8 | 1.02 (0.90–1.17) | 1.02 (0.90–1.17) | 0.00 | 0.64 |
| Females only | 8 | 1.11 (1.00–1.25) | 1.06 (0.89–1.26) | 0.41 | 0.15 |
| Incidence-only studies | 7 | 0.90 (0.77–1.04) | 0.90 (0.77–1.04) | 0.00 | 0.70 |
| Colon | |||||
| All studies | 11 | 1.08 (1.02–1.13) | 1.08 (1.02–1.13) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.94 |
| Case–control studies | 5 | 1.05 (0.99–1.12) | 1.05 (0.99–1.12) | 0.00 | 0.71 |
| Males only | 8 | 1.04 (0.96–1.12) | 1.07 (0.95–1.22) | 0.43 | 0.14 |
| Females only | 9 | 1.10 (1.03–1.16) | 1.10 (1.03–1.16) | 0.00 | 0.83 |
| Incidence-only studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.99 |
| Liver | |||||
| All studies | 8 | 1.39 (1.29–1.51) | 1.17 (0.90–1.53) | 0.80 | 0.02 |
| Cohort studies | 5 | 1.05 (0.86–1.27) | 1.05 (0.86–1.27) | 0.00 | 0.76 |
| Case–control studies | 3 | 1.48 (1.35–1.61) | 1.07 (0.59–1.94) | 0.97 | 0.08 |
| Males only | 7 | 1.49 (1.37–1.63) | 1.49 (1.37–1.63) | 0.00 | 0.50 |
| Females only | 4 | 0.96 (0.78–1.17) | 0.96 (0.78–1.17) | 0.00 | 0.81 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
| Pancreas | |||||
| All studies | 9 | 1.11 (1.02–1.20) | 1.08 (0.90–1.29) | 0.63 | 0.05 |
| Cohort studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
| Case–control studies | 3 | 1.06 (0.96–1.17) | 0.75 (0.40–1.41) | 0.96 | 0.06 |
| Males only | 8 | 0.91 (0.80–1.04) | 1.06 (0.74–1.52) | 0.81 | 0.001 |
| Females only | 8 | 1.20 (1.09–1.32) | 1.20 (1.09–1.32) | 0.00 | 0.65 |
| Incidence-only studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Oesophagus | |||||
| All studies | 10 | 0.87 (0.74–1.03) | 0.87 (0.74–1.03) | 0.00 | 0.78 |
| Cohort studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Case–control studies | 3 | 0.83 (0.69–1.00) | 0.83 (0.69–1.00) | 0.00 | 0.41 |
| Males only | 8 | 0.90 (0.73–1.10) | 0.90 (0.73–1.10) | 0.00 | 0.46 |
| Females only | 6 | 0.84 (0.65–1.09) | 0.84 (0.65–1.09) | 0.00 | 0.98 |
| Incidence-only studies | 7 | 1.04 (0.73–1.48) | 1.04 (0.73–1.48) | 0.00 | 0.87 |
| Stomach | |||||
| All studies | 10 | 1.08 (0.99–1.18) | 1.04 (0.91–1.19) | 0.42 | 0.10 |
| Cohort studies | 6 | 0.89 (0.77–1.04) | 0.89 (0.77–1.04) | 0.00 | 0.59 |
| Case–control studies | 4 | 1.19 (1.07–1.32) | 1.19 (1.07–1.32) | 0.00 | 0.76 |
| Males only | 8 | 1.02 (0.90–1.17) | 1.02 (0.90–1.17) | 0.00 | 0.64 |
| Females only | 8 | 1.11 (1.00–1.25) | 1.06 (0.89–1.26) | 0.41 | 0.15 |
| Incidence-only studies | 7 | 0.90 (0.77–1.04) | 0.90 (0.77–1.04) | 0.00 | 0.70 |
| Colon | |||||
| All studies | 11 | 1.08 (1.02–1.13) | 1.08 (1.02–1.13) | 0.00 | 0.92 |
| Cohort studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.94 |
| Case–control studies | 5 | 1.05 (0.99–1.12) | 1.05 (0.99–1.12) | 0.00 | 0.71 |
| Males only | 8 | 1.04 (0.96–1.12) | 1.07 (0.95–1.22) | 0.43 | 0.14 |
| Females only | 9 | 1.10 (1.03–1.16) | 1.10 (1.03–1.16) | 0.00 | 0.83 |
| Incidence-only studies | 6 | 1.11 (1.03–1.20) | 1.11 (1.03–1.20) | 0.00 | 0.99 |
| Liver | |||||
| All studies | 8 | 1.39 (1.29–1.51) | 1.17 (0.90–1.53) | 0.80 | 0.02 |
| Cohort studies | 5 | 1.05 (0.86–1.27) | 1.05 (0.86–1.27) | 0.00 | 0.76 |
| Case–control studies | 3 | 1.48 (1.35–1.61) | 1.07 (0.59–1.94) | 0.97 | 0.08 |
| Males only | 7 | 1.49 (1.37–1.63) | 1.49 (1.37–1.63) | 0.00 | 0.50 |
| Females only | 4 | 0.96 (0.78–1.17) | 0.96 (0.78–1.17) | 0.00 | 0.81 |
| Incidence-only studies | 4 | 0.95 (0.85–1.07) | 0.95 (0.85–1.07) | 0.00 | 0.64 |
| Pancreas | |||||
| All studies | 9 | 1.11 (1.02–1.20) | 1.08 (0.90–1.29) | 0.63 | 0.05 |
| Cohort studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
| Case–control studies | 3 | 1.06 (0.96–1.17) | 0.75 (0.40–1.41) | 0.96 | 0.06 |
| Males only | 8 | 0.91 (0.80–1.04) | 1.06 (0.74–1.52) | 0.81 | 0.001 |
| Females only | 8 | 1.20 (1.09–1.32) | 1.20 (1.09–1.32) | 0.00 | 0.65 |
| Incidence-only studies | 6 | 1.22 (1.05–1.42) | 1.18 (0.95–1.46) | 0.38 | 0.21 |
aProportion of total variance due to between-study variance.
Respiratory cancers
We retrieved 18 studies on lung cancer and 12 on larynx cancer (Table 5).43,48,49,51,53,55,56,90,92,93,95–101 We observed an increase in the risk of lung cancer that rounded to 30% (Table 10). Except when restricted to male studies, this increase did not subside after stratification. The effect was higher among cohort studies, female studies, incidence studies and those studies that adjusted for smoking.
Pooled RRs and 95% CIs of respiratory cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Lung | |||||
| All studies | 18 | 1.18 (1.14–1.22) | 1.27 (1.15–1.41) | 0.78 | 0.0001 |
| Cohort studies | 8 | 1.32 (1.23–1.41) | 1.32 (1.23–1.42) | 0.05 | 0.40 |
| Case–control studies | 10 | 1.13 (1.09–1.18) | 1.29 (1.04–1.61) | 0.93 | 0.0006 |
| Males only | 12 | 0.96 (0.92–1.06) | 1.12 (0.94–1.33) | 0.89 | 0.0001 |
| Females only | 14 | 1.34 (1.28–1.41) | 1.40 (1.24–1.59) | 0.70 | 0.006 |
| Smoking adjusted | 4 | 1.36 (1.16–1.60) | 1.36 (1.08–1.70) | 0.43 | 0.19 |
| Smoking non-adjusted | 14 | 1.17 (1.13–1.21) | 1.25 (1.12–1.40) | 0.81 | 0.0001 |
| Incidence-only studies | 8 | 1.32 (1.23–1.42) | 1.32 (1.22–1.43) | 0.06 | 0.37 |
| Mortality-only studies | 10 | 1.14 (1.09–1.19) | 1.24 (1.04–1.48) | 0.91 | 0.0001 |
| Larynx | |||||
| All studies | 12 | 1.32 (1.10–1.59) | 1.52 (1.11–2.08) | 0.52 | 0.04 |
| Cohort studies | 7 | 1.68 (1.31–2.17) | 1.70 (1.25–2.32) | 0.23 | 0.27 |
| Case–control studies | 5 | 1.02 (0.79–1.33) | 1.18 (0.66–2.11) | 0.63 | 0.17 |
| Males only | 11 | 1.25 (1.01–1.54) | 1.30 (0.93–1.81) | 0.47 | 0.06 |
| Females only | 5 | 1.67 (1.17–2.37) | 2.36 (1.03–5.40) | 0.75 | 0.03 |
| Smoking adjusted | 2 | 2.18 (1.00–4.71) | 2.18 (1.00–4.71) | 0.00 | 0.69 |
| Smoking non-adjusted | 10 | 1.28 (1.06–1.55) | 1.46 (1.04–2.06) | 0.58 | 0.02 |
| Incidence-only studies | 9 | 1.74 (1.37–2.22) | 1.75 (1.36–2.26) | 0.05 | 0.39 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Lung | |||||
| All studies | 18 | 1.18 (1.14–1.22) | 1.27 (1.15–1.41) | 0.78 | 0.0001 |
| Cohort studies | 8 | 1.32 (1.23–1.41) | 1.32 (1.23–1.42) | 0.05 | 0.40 |
| Case–control studies | 10 | 1.13 (1.09–1.18) | 1.29 (1.04–1.61) | 0.93 | 0.0006 |
| Males only | 12 | 0.96 (0.92–1.06) | 1.12 (0.94–1.33) | 0.89 | 0.0001 |
| Females only | 14 | 1.34 (1.28–1.41) | 1.40 (1.24–1.59) | 0.70 | 0.006 |
| Smoking adjusted | 4 | 1.36 (1.16–1.60) | 1.36 (1.08–1.70) | 0.43 | 0.19 |
| Smoking non-adjusted | 14 | 1.17 (1.13–1.21) | 1.25 (1.12–1.40) | 0.81 | 0.0001 |
| Incidence-only studies | 8 | 1.32 (1.23–1.42) | 1.32 (1.22–1.43) | 0.06 | 0.37 |
| Mortality-only studies | 10 | 1.14 (1.09–1.19) | 1.24 (1.04–1.48) | 0.91 | 0.0001 |
| Larynx | |||||
| All studies | 12 | 1.32 (1.10–1.59) | 1.52 (1.11–2.08) | 0.52 | 0.04 |
| Cohort studies | 7 | 1.68 (1.31–2.17) | 1.70 (1.25–2.32) | 0.23 | 0.27 |
| Case–control studies | 5 | 1.02 (0.79–1.33) | 1.18 (0.66–2.11) | 0.63 | 0.17 |
| Males only | 11 | 1.25 (1.01–1.54) | 1.30 (0.93–1.81) | 0.47 | 0.06 |
| Females only | 5 | 1.67 (1.17–2.37) | 2.36 (1.03–5.40) | 0.75 | 0.03 |
| Smoking adjusted | 2 | 2.18 (1.00–4.71) | 2.18 (1.00–4.71) | 0.00 | 0.69 |
| Smoking non-adjusted | 10 | 1.28 (1.06–1.55) | 1.46 (1.04–2.06) | 0.58 | 0.02 |
| Incidence-only studies | 9 | 1.74 (1.37–2.22) | 1.75 (1.36–2.26) | 0.05 | 0.39 |
aProportion of total variance due to between-study variance.
Pooled RRs and 95% CIs of respiratory cancers among hairdressers and related occupations
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Lung | |||||
| All studies | 18 | 1.18 (1.14–1.22) | 1.27 (1.15–1.41) | 0.78 | 0.0001 |
| Cohort studies | 8 | 1.32 (1.23–1.41) | 1.32 (1.23–1.42) | 0.05 | 0.40 |
| Case–control studies | 10 | 1.13 (1.09–1.18) | 1.29 (1.04–1.61) | 0.93 | 0.0006 |
| Males only | 12 | 0.96 (0.92–1.06) | 1.12 (0.94–1.33) | 0.89 | 0.0001 |
| Females only | 14 | 1.34 (1.28–1.41) | 1.40 (1.24–1.59) | 0.70 | 0.006 |
| Smoking adjusted | 4 | 1.36 (1.16–1.60) | 1.36 (1.08–1.70) | 0.43 | 0.19 |
| Smoking non-adjusted | 14 | 1.17 (1.13–1.21) | 1.25 (1.12–1.40) | 0.81 | 0.0001 |
| Incidence-only studies | 8 | 1.32 (1.23–1.42) | 1.32 (1.22–1.43) | 0.06 | 0.37 |
| Mortality-only studies | 10 | 1.14 (1.09–1.19) | 1.24 (1.04–1.48) | 0.91 | 0.0001 |
| Larynx | |||||
| All studies | 12 | 1.32 (1.10–1.59) | 1.52 (1.11–2.08) | 0.52 | 0.04 |
| Cohort studies | 7 | 1.68 (1.31–2.17) | 1.70 (1.25–2.32) | 0.23 | 0.27 |
| Case–control studies | 5 | 1.02 (0.79–1.33) | 1.18 (0.66–2.11) | 0.63 | 0.17 |
| Males only | 11 | 1.25 (1.01–1.54) | 1.30 (0.93–1.81) | 0.47 | 0.06 |
| Females only | 5 | 1.67 (1.17–2.37) | 2.36 (1.03–5.40) | 0.75 | 0.03 |
| Smoking adjusted | 2 | 2.18 (1.00–4.71) | 2.18 (1.00–4.71) | 0.00 | 0.69 |
| Smoking non-adjusted | 10 | 1.28 (1.06–1.55) | 1.46 (1.04–2.06) | 0.58 | 0.02 |
| Incidence-only studies | 9 | 1.74 (1.37–2.22) | 1.75 (1.36–2.26) | 0.05 | 0.39 |
| . | Number of studies . | RR (95% CI) fixed effects . | RR (95% CI) random effects . | Ria . | Q-test P-value . |
|---|---|---|---|---|---|
| Lung | |||||
| All studies | 18 | 1.18 (1.14–1.22) | 1.27 (1.15–1.41) | 0.78 | 0.0001 |
| Cohort studies | 8 | 1.32 (1.23–1.41) | 1.32 (1.23–1.42) | 0.05 | 0.40 |
| Case–control studies | 10 | 1.13 (1.09–1.18) | 1.29 (1.04–1.61) | 0.93 | 0.0006 |
| Males only | 12 | 0.96 (0.92–1.06) | 1.12 (0.94–1.33) | 0.89 | 0.0001 |
| Females only | 14 | 1.34 (1.28–1.41) | 1.40 (1.24–1.59) | 0.70 | 0.006 |
| Smoking adjusted | 4 | 1.36 (1.16–1.60) | 1.36 (1.08–1.70) | 0.43 | 0.19 |
| Smoking non-adjusted | 14 | 1.17 (1.13–1.21) | 1.25 (1.12–1.40) | 0.81 | 0.0001 |
| Incidence-only studies | 8 | 1.32 (1.23–1.42) | 1.32 (1.22–1.43) | 0.06 | 0.37 |
| Mortality-only studies | 10 | 1.14 (1.09–1.19) | 1.24 (1.04–1.48) | 0.91 | 0.0001 |
| Larynx | |||||
| All studies | 12 | 1.32 (1.10–1.59) | 1.52 (1.11–2.08) | 0.52 | 0.04 |
| Cohort studies | 7 | 1.68 (1.31–2.17) | 1.70 (1.25–2.32) | 0.23 | 0.27 |
| Case–control studies | 5 | 1.02 (0.79–1.33) | 1.18 (0.66–2.11) | 0.63 | 0.17 |
| Males only | 11 | 1.25 (1.01–1.54) | 1.30 (0.93–1.81) | 0.47 | 0.06 |
| Females only | 5 | 1.67 (1.17–2.37) | 2.36 (1.03–5.40) | 0.75 | 0.03 |
| Smoking adjusted | 2 | 2.18 (1.00–4.71) | 2.18 (1.00–4.71) | 0.00 | 0.69 |
| Smoking non-adjusted | 10 | 1.28 (1.06–1.55) | 1.46 (1.04–2.06) | 0.58 | 0.02 |
| Incidence-only studies | 9 | 1.74 (1.37–2.22) | 1.75 (1.36–2.26) | 0.05 | 0.39 |
aProportion of total variance due to between-study variance.
The pooled estimates of the 12 studies on larynx cancer show a considerable increase in the risk (random effects pooled RR 1.52, 95% CI 1.11–2.08). This risk is higher when we restricted the analysis to cohort studies (RR 1.68; 95% CI 1.31–2.17) and female studies (RR 2.36, 95% CI 1.03–5.40). The two studies that adjusted for smoking showed an RR of 2.36 (95% CI 1.03–5.40).
Brain, skin and salivary gland cancers
In addition to cancers of specific sites presented above, nine studies were available for brain cancer51,52,55,93,95,102 and seven for melanoma.51,52,55,56,93 The pooled estimates were 1.12 (95% CI 1.02–1.24) for brain and 1.03 (95% CI 0.92–1.14) for melanoma. These results did not change substantially after stratification by design or gender.
We also found one study that shows that female hairdressers have an elevated risk of salivary gland cancer (RR 2.7, 95% CI 1.1–6.5).103
Assessment of publication bias
We did not find evidence of publication bias by examining the funnel plots of the anatomic sites with sufficient number of studies (data not shown, available from first author). We observed some asymmetry on the funnel plots of the studies on lung and bladder cancers. In both cases asymmetry was caused by the extreme result of one study.92,99
Except for multiple myeloma (P = 0.03), the regression test of asymmetry yielded inconclusive results for haematopoietic cancers (P = 0.08 for all sites together, 0.33 for Hodgkin's disease, 0.84 for non-Hodgkin's lymphoma, and 0.98 for leukaemia).
To further evaluate the possibility of publication bias in case–control studies, a design that is more probably disregarded by authors and editors in case of null or statistically non-significant results, we performed a sensitivity analysis by recalculating our pooled estimates under the following extreme assumptions: (i) published case–control studies are only half of the studies of occupation as hairdresser and cancer ever conducted; (ii) all unpublished studies found an RR of 1; and (iii) the unpublished studies included as many cases and controls as the average of the published studies. Under these assumptions, the pooled estimates still show a moderate increase in the risk: RR 1.23 (95% CI 1.12–1.34) for lung cancer, RR 1.29 (95% CI 1.04–1.60) for larynx cancer, RR 1.06 (95% CI 1.02–1.10) for bladder cancer, RR 1.06 (95% CI 1.02–1.09) for all haematopoietic cancers, RR 1.12 (95% CI 1.03–1.23) for multiple myeloma.
To check for any change in the pooled estimates that may have occurred after the ban of the most important carcinogenic agents (2,4-diaminotoluene and 2,4-diaminoanisole) from hair dyes in the mid-1970s,3 we restricted our analysis to those studies carried out before this date and compared their pooled estimates with those of the general analysis. We did not find any substantial difference between the results. We could not compare the pooled estimates before and after the ban of those agents as occupational exposure of studies carried out recently may have taken place before the ban.
Discussion
The high number of studies included in our meta-analysis and the consistency of results across anatomic sites and design settings provide strong evidence that cancer risk is higher among employees of the hairdressing industry.
The magnitude of the risk increase is substantial in several anatomic sites: 62% for multiple myeloma, 52% for larynx, 30% for bladder and 27% for lung cancer. The fact that the risk increase is observed for cancers of different anatomic sites may be explained by the existence of multiple exposure pathways (respiratory, dermatologic and systemic). It is also likely that some cancers, such as lung and bladder cancer, may share a common aetiology.
Nevertheless, alternative explanations for the risk increase deserve careful examination. Confounding by known or unknown factors is a non-causal explanation that is often argued to explain associations in meta-analyses. To act as a confounder, a factor must be related to exposure and disease. Besides age and sex, smoking is traditionally considered as the most important potential confounder of the association of any exposure factor with cancer. There is some evidence that smoking is more frequent among hairdressers than among the general population.54,104 However, when we restricted the analysis to those studies that adjusted for tobacco consumption, the magnitude of the association between occupation as a hairdresser and cancer did not decrease. On the contrary, the risk increased in those cancers that are known to be strongly linked to tobacco use (lung, larynx and bladder).
Potential confounding by alcohol is unlikely to occur as there is some evidence that alcohol intake is not higher among hairdressers.104 Unidentified genetic factors are not likely to introduce confounding as this would imply that the election of the hairdressing occupation by a subject is driven by genetic factors, a hypothesis that is biologically not plausible. Genotypic and phenotypic factors may, however, act as effect modifiers of the relation between occupational exposure as a hairdresser and cancer. This would lead to RRs between hairdressing and cancer that are of different magnitudes across alleles. This feature was previously described for N-acetyltransferase-2 (NAT2) phenotype and NAT1*10 allele, and bladder cancer and non-Hodgkin lymphoma among users of hair dyes.105,106
The existence of another unidentified factor associated with both the hairdresser occupation and cancer, which could explain the relation observed, is unlikely. Even if this unidentified factor could double the risk of cancer among subjects exposed to it (RR confounder–disease = 2) and, simultaneously, this factor happened to be twice more prevalent among hairdressers than among other occupations (RR confounder–exposure = 2), the adjusted RR of the relation hairdresser occupation–cancer would still be 1.13 for lung cancer, 1.35 for larynx cancer, 1.21 for bladder cancer and 1.44 for multiple myeloma (assuming one-third of people are exposed to this unknown factor).107 The existence of an unknown factor so strongly related with the hairdresser profession and with cancer, without being a chemical agent present in the occupational environment of a hairdresser, is highly improbable.
The overwhelming majority of the studies included in this meta-analysis were carried out in the USA and Europe, with the exception of Japan and New Zealand. The conclusions may then not generalize to other populations.
Our meta-analysis may be limited by the fact that we included studies that used information systems, such as death certificates, that may present incomplete information on confounders and occupational exposure.32 We overcame this caveat by restricting, in a second stage, our analysis to studies that measured incidence only, and excluding studies based on death certificates. The results did not change substantially.
Except for the very limited assessment of duration of employment in four bladder cancer studies, we could not assess the existence of a dose–response gradient as no data were available on duration of employment or exposure intensity in the studies included in this meta-analysis.
Hairdressers are chronically exposed to potentially harmful chemicals contained in hair dyes. The use of the most aggressive agents was discontinued three decades ago. A deceleration in the risk increase is then expectable in those studies carried out partially or completely after this ban. We were not able to find evidence of this change. It is then probable that hairdressers and allied occupations continue to be exposed to DNA-damaging agents other than those contained in hair dyes, such as formaldehyde, metacrylate and acetone, the concentration of which may be excessive in the air of hairdresser salons.104 IARC does not attribute specific causality of carcinogenicity among hairdressers to hair dying agents, but does mention that over 5000 chemicals are present in the environment of these workers.15 Also, it should be mentioned that due to the long latency period between exposure or its removal and the occurrence of cancer, the comparison of studies carried out between and after the ban is not straightforward. If an effect exists, only the most recent studies and, more probably, the forthcoming studies may provide evidence if the banned problematic hair dyes were involved in increased cancer risks in hairdressers or not.
The fact that cosmetics are generally exempted from the labelling information that is required for other chemicals increases potential hazard in subjects frequently exposed to them.31 In fact, detection and prevention measures related to industrial hygiene have only recently been instituted in hairdressing and nail care salons.108 A recent study found that none of the hairdresser salons surveyed in central and suburban areas of a large city had any ventilation system.109 Furthermore, it is remarkable that only about one-third of hairdressers in Nordic countries have used protective gloves while using hair dyes.110
In conclusion, our results show that hairdressers and allied occupations have a higher risk of cancer than the general population. The risk increase is substantial for lung, larynx, bladder cancer and multiple myeloma and less marked for Hodgkin's disease, non-Hodgkin's lymphoma, leukaemia, ovary, breast, kidney and colon cancer. Improvement of the ventilation system in the hairdresser salons and implementation of hygiene measures aimed at mitigating exposure to potential carcinogens at work may reduce the risk.
Funding
Takkouche, Montes-Martínez and Regueira-Méndez are employees of the University of Santiago de Compostela (Spain) and have grants from ‘CIBER en Epidemiología y Salud Pública’ (CIBER-ESP), Spain, a public centre affiliated to the Spanish Ministry of Health. Dr Takkouche's work on risk factors of haematopoietic cancers is funded by grant A/019761/08 of the International Cooperation Programme of the Spanish Ministry of Foreign Affairs. No special funding was received for this study.
Acknowledgement
The authors thank Dr Vincent Cogliano from IARC (Lyon, France) for providing studies that we could not find in our original search.
Conflict of interest: None declared.
Hairdressers and allied occupations have a higher risk of cancer than the general population.
The risk increase is particularly marked for lung, larynx and bladder cancer and multiple myeloma.
Improvement of the ventilation system in hairdresser salons and implementation of hygiene measures aimed at mitigating exposure to potential carcinogens at work are probably the best preventive tools.