Objective

We compared, updated, and expanded the analyses of two previous meta-analyses of personal hair dye exposure and bladder cancer, and briefly discussed the biological plausibility of a systemic hazard to human health from exposure to para-phenylenediamine (PPD), a key chemical in hair dyes.

Methods

The meta-analysis included 11 case–control studies and one cohort study. We evaluated heterogeneity across studies and conducted sensitivity and influence analyses.

Results

No association was found between any personal use of hair dye and bladder cancer among women (meta-relative risk [mRR] = 1.01, 95% CI: 0.89–1.14), men (mRR = 0.82, 95% CI: 0.60–1.14), or both sexes combined (mRR = 0.97, 95% CI: 0.87–1.08). No statistically significant mRRs were found among the studies that reported data for permanent hair dye use (mRR = 1.06, 95% CI: 0.89–1.27), duration of any hair dye use (mRR = 1.00, 95% CI: 0.85–1.19), duration of permanent hair dye use (mRR = 1.31 95% CI 0.78–2.19), lifetime applications of any hair dye use (mRR = 1.12 (95% CI: 0.72–1.72) or permanent hair dye use (mRR = 1.59, 95% CI 0.69–3.64), or dark color hair dye use (mRR = 0.94, 95% CI: 0.74–1.19).

Conclusion

The results of this meta-analysis of epidemiologic studies do not indicate a causal association between personal hair dye use and bladder cancer.