title: Bladder cancer among hairdressers: a meta-analysis.
abstract: BACKGROUND
  Occupational risks for bladder cancer in hairdressers by using hair products have been examined in many epidemiological studies. But owing to small sample sizes of the studies and the resulting lack of statistical power, the results of these studies have been inconsistent and significant associations have rarely been found.
  
  
  METHODS
  We conducted a meta-analysis to determine summary risk ratios (SRRs) for the risk of bladder cancer among hairdressers. Studies were identified by a MEDLINE, EMBASE, CENTRAL search and by the reference lists of articles/relevant reviews. Statistical tests for publication bias and for heterogeneity as well as sensitivity analysis were applied. In addition, the study quality and the risk of bias were assessed using six criteria.
  
  
  RESULTS
  42 studies were included and statistically significantly increased risks around 1.3-1.7 were found for all but one analysis. The SRR increased with duration of employment from 1.30 (95% CI 1.15 to 1.48) for 'ever registered as hairdresser' to 1.70 (95% CI 1.01 to 2.88) for 'job held > or = 10 years'. No difference was found between the risk for smoking-adjusted data (SRR 1.35, 95% CI 1.13 to 1.61) and no adjustment (SRR 1.33, 95% CI 1.18 to 1.50). Studies assessed as being of high quality (n=11) and of moderate quality (n=31) showed similar SRRs. There was no evidence of publication bias or heterogeneity in all analyses.
  
  
  CONCLUSIONS
  In summary, our results showed an increased and statistically significant risk for bladder cancer among hairdressers, in particular for hairdressers in jobs held > or = 10 years. Residual confounding by smoking cannot be totally ruled out. Because of the long latency times of bladder cancer it remains an open question whether hairdressers working prior to 1980 and after 1980, when some aromatic amines were banned as hair dye ingredients, have the same risk for bladder cancer.
authors.affiliation: Institution for Statutory Accident Insurance and Prevention in the Health and Welfare Services, Department of Occupational Health Research, Pappelallee 35/37, Hamburg 22089, Germany. melanie.harling@bgw-online.de
authors.forename: Melanie
authors.initials: M
authors.lastname: Harling
authors.forename: Anja
authors.initials: A
authors.lastname: Schablon
authors.forename: Grita
authors.initials: G
authors.lastname: Schedlbauer
authors.forename: Madeleine
authors.initials: M
authors.lastname: Dulon
authors.forename: Albert
authors.initials: A
authors.lastname: Nienhaus
mesh_terms: D000588:Amines / Q000633:toxicity*; D005260:Female; D006202:Hair Dyes / Q000633:toxicity*; D006801:Humans; D015994:Incidence; D008297:Male; D016273:Occupational Exposure / Q000009:adverse effects*; D012307:Risk Factors; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced / Q000453:epidemiology*
chemical_list: D000588:Amines; D006202:Hair Dyes
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