title: Personal use of hair dyes and the risk of bladder cancer: results of a meta-analysis.
abstract: OBJECTIVE
  This study examined the methodology of observational studies that explored an association between personal use of hair dye products and the risk of bladder cancer.
  
  
  METHODS
  Data were pooled from epidemiological studies using a general variance-based meta-analytic method that employed confidence intervals. The outcome of interest was a summary relative risk (RRs) reflecting the risk of bladder cancer development associated with use of hair dye products vs. non-use. Sensitivity analyses were performed to explain any observed statistical heterogeneity and to explore the influence of specific study characteristics of the summary estimate of effect.
  
  
  RESULTS
  Initially combining homogenous data from six case-control and one cohort study yielded a non-significant RR of 1.01 (0.92, 1.11), suggesting no association between hair dye use and bladder cancer development. Sensitivity analyses examining the influence of hair dye type, color, and study design on this suspected association showed that uncontrolled confounding and design limitations contributed to a spurious non-significant summary RR. The sensitivity analyses yielded statistically significant RRs ranging from 1.22 (1.11, 1.51) to 1.50 (1.30, 1.98), indicating that personal use of hair dye products increases bladder cancer risk by 22% to 50% vs. non-use.
  
  
  CONCLUSIONS
  The available epidemiological data suggest an association between personal use of hair dye products and increased risk of bladder cancer.
authors.affiliation: Division of Radiation Oncology, Department of Clinical Oncology, Marshfield Clinic Cancer Center, Marshfield, WI, USA. Huncharek.Michael@Marshfieldclinic.org
authors.forename: Michael
authors.initials: M
authors.lastname: Huncharek
authors.forename: Bruce
authors.initials: B
authors.lastname: Kupelnick
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D015331:Cohort Studies; D015981:Epidemiologic Factors; D005260:Female; D006202:Hair Dyes / Q000009:adverse effects*; D006801:Humans; D008297:Male; D019370:Observation / Q000379:methods; D012107:Research Design; D012306:Risk; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced* / Q000453:epidemiology*
chemical_list: D006202:Hair Dyes
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