Personal use of hair dyes and risk of leukemia: a systematic literature review and meta-analysis.

The objective of this study was to examine the association between personal use of hair dyes and the risk of leukemia. We conducted a systematic literature review of epidemiology studies reporting leukemia-specific cancer risks among hair dye users, and estimated the meta-relative risk (meta-RR) and corresponding 95% confidence interval (95% CI) of leukemia, comparing hair dye users to nonusers. When data from all 20 studies that met the inclusion criteria were combined, ever use of hair dye was associated with a nonstatistically significant increased risk of leukemia, meta-RR = 1.09 (95% CI: 0.97-1.22). When restricted to studies that adjusted for smoking, ever use of hair dye was not associated with leukemia, meta-RR = 0.99 (95% CI: 0.76-1.29). A statistically significant increased risk of leukemia was associated with permanent hair dye use (meta-RR = 1.19 [95% CI: 1.07-1.33]), dark hair dye use (meta-RR = 1.29 [95% CI: 1.11-1.50]), hair dye use among males (meta-RR = 1.42 [95% CI: 1.01-2.00]), hair dye use pre-1980 (meta-RR = 1.49 [95% CI: 1.21-1.83]), and hair dye use for ≥15 years (meta-RR = 1.35 [95% CI: 1.13-1.62]). Overall, findings suggest that ever use of hair dye is not a significant risk factor for leukemia. Certain hair dye use characteristics were associated with a statistically significant increased risk, but further research is required to determine whether these associations truly reflect a risk of leukemia due to methodological limitations in the underlying studies.