Use of hair dyes has been suggested recently as a risk factor for several
types of cancer in epidemiologic studies. This alarming news and controversial
declarations by scientific organizations and general media have made necessary
a systematic evaluation of the epidemiologic evidence.
To examine the association between personal use of hair dyes and relative
risk of cancer.
We retrieved studies published in any language by systematically searching
the MEDLINE (1966–January 2005), EMBASE, LILACS, and ISI Proceedings
computerized databases and by manually examining the references of the original
articles, reviews, and monographs retrieved.
We included cohort and case-control studies reporting relative risk
estimates and 95% confidence intervals (CIs) (or data to calculate them) of
personal hair dye use and cancer. We excluded studies that dealt with occupational
exposure. We carried out separate analyses for bladder, breast, and hematopoietic
cancers and cancers of other sites. Seventy-nine studies were included of
210 articles identified in the search.
Data were extracted independently by 2 investigators. We used a standardized
questionnaire to record information on study design, sample size, type of
controls, year of publication, adjustment factors, and relative risks of cancer
among ever users of hair dyes. When possible, we extracted association measures
on use of permanent dyes and extensive use (>200 lifetime episodes of dye
Study-specific relative risks were weighted by the inverse of their
variance to obtain fixed- and random-effects pooled estimates. The pooled
relative risk for ever users of hair dyes was 1.06 (95% CI, 0.95-1.18) for
breast cancer (14 studies), 1.01 (95% CI, 0.89-1.14) for bladder cancer (10
studies), and 1.15 (95% CI, 1.05-1.27) for hematopoietic cancers (40 studies).
Other cancers were examined by only 1 or 2 studies, of which the pooled or
single relative risk was elevated for brain cancer, ovarian cancer, and cancer
of the salivary glands. No effect was observed for use of permanent dyes or
for extensive use.
We did not find strong evidence of a marked increase in the risk of
cancer among personal hair dye users. Some aspects related to hematopoietic
cancer and other cancers that have shown evidence of increased risk in 1 or
2 studies should be investigated further.