Personal use of hair dyes and risk of cancer: a meta-analysis.
BACKGROUND
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.


OBJECTIVE
To examine the association between personal use of hair dyes and relative risk of cancer.


METHODS
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.


METHODS
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.


METHODS
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 use).


RESULTS
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.


CONCLUSIONS
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.
Takkouche
Bahi
B
Department of Preventive Medicine, University of Santiago de Compostela, Santiago de Compostela, Spain. mrbahi@usc.es
Etminan
Mahyar
M
Montes-Martínez
Agustín
A
D001943:Breast Neoplasms / Q000139:chemically induced / Q000453:epidemiology; D006202:Hair Dyes / Q000009:adverse effects*; D019337:Hematologic Neoplasms / Q000139:chemically induced / Q000453:epidemiology; D006801:Humans; D009369:Neoplasms / Q000139:chemically induced* / Q000453:epidemiology*; D012307:Risk Factors; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced / Q000453:epidemiology
D006202:Hair Dyes