Personal hair dye use and bladder cancer: a meta-analysis

Despite considerable research, the issue of hair dyes and bladder cancer is still open to discussion. In January 2013, we searched in PubMed/EMBASE to identify observational studies investigating the association between personal use of hair dyes and bladder cancer incidence/mortality. Pooled relative risks (RRs) and corresponding 95% confidence intervals (CIs) were calculated using random-effects models. Fifteen case-control and two cohort studies were available for meta-analysis (8504 cases/deaths, 14,102 controls, and 617,937 persons at risk). Compared with no use, the pooled RR of bladder cancer for personal use of any type of hair dyes was 0.93 (95% CI, 0.82-1.05), with moderate heterogeneity among studies (I2 = 34.1%, P = 07). Similar RRs were found for females (RR = 0.95) and males (RR = 0.81). Based on seven studies, the pooled RR for personal use of permanent hair dyes was 0.92 (95% CI, 0.77-1.09). Compared with no use, no association was observed for the highest categories of duration of use and lifetime frequency of use of both any type of dyes and permanent dyes. The pooled RR from four studies reporting results for use of dark-colored dyes was 1.29 (95% CI, 0.98-1.71). This meta-analysis allows to definitively exclude any appreciable excess risk of bladder cancer among personal hair dye users.