Bladder cancer risk and personal hair dye use

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Abstract
Several cohort and case‐control studies have found an increased risk of bladder cancer among hairdressers and barbers who are occupationally exposed to hair dyes. However, the carcinogenic risk associated with personal use of hair dyes remains uncertain since several large case‐control and cohort studies did not find an association between personal hair dye use and bladder cancer. To address this question, the authors used data collected on 459 bladder cancer cases and 665 controls who were interviewed as part of a case‐control study conducted in New Hampshire between 1994 and 1998. Participants underwent a structured personal interview with regard to history of hair dye use and bladder cancer risk factors. Unconditional logistic regression analysis was used to compute odds ratios that were associated with hair dye use, while controlling for potential confounding factors. A history of any hair dye use was inversely associated with bladder cancer incidence in men [adjusted odds ratio (OR) = 0.5; 95% confidence interval (CI)=0.3–0.8], although risk reductions were not statistically significant for individual dye types. In women, use of permanent (adjusted OR = 1.5; 95%CI = 0.8–2.7) and rinse‐type hair dye (adjusted OR = 1.7; 95%CI = 0.8–3.6) were associated with a modestly elevated risk of bladder cancer but with limited statistical precision; no association was found with use of semi‐permanent dyes (adjusted OR = 0.7; 95%CI = 0.3–1.4). For permanent hair dye use, odds ratios were most pronounced for younger age at first use, higher frequency and prolonged time since first use; however there were no clear trends in risk by these factors. In light of the prevalence of hair dye use, further studies are needed that address the effects of specific colors and types of hair dyes along with the possible role of individual susceptibility.