Use of permanent hair dyes and bladder‐cancer risk

Dear Sir, Thecase-contro l study by Gago-Domingue z et al.1 raises the possibility that useof permanen t hair dyemay increase the risk of bladder cancer . In that study, the odds ratio (OR) associated with developing incident bladder cancer among women who ever used permanen t hair dye was 1.9 (95% CI 5 1.1– 3.3) compared to nonuser s and was 3.7 (95% CI 5 1.2–11.2) among those with more than 30 years of use. Women who never smoked had ahigher relative risk (OR52.7) compared to women who ever smoked (OR51.4), although this difference was not statisticall y significant . The authors sugges t that hair dye causes 19% of bladder cancer s in women in Los Angeles County, California. We have previousl y reported no association between the use of permanen t hair dye and deat h from bladder cancer in a prospective study of approximatel y 600,000 women that participated in Cancer Prevention Study II , a cohort study begun by the American Cancer Societ y in 1982.2,3 The age-standardized rate ratio (RR) associate d with ever use of hair dye after 7 years of follow-up (based on 84 deaths among never users and 15 deaths among ever users) was 0.56 (95% CI5 0.32–0.99) and after 12 years of follow-up was 1.0 (95% CI50.7–1.4), based on 154 and 48 deaths among never and ever users, respectively. We now report the results after 16 years of follow-up. The present analysi s is based on 547,571 women who were cancer-fre (excepting non-melanomaskin cancer ) in 1982 and who reported complet e information on race, hair dye use and smoking status. After 16 years of follow-up, 131,039 women had died (19.4%) and 543,171 were alive (80.3%). Follow-up of 2,078 women was truncated on Septembe r 1, 1988. Information on hair dye use was based on questionnaire response s in 1982 and was not updated during the follow-up. Women were asked “Do you now or have you ever used permanen t hair dye? ” Those who reported hair dye use were asked the following open-ende d questions : (i) “What brand? ”, (ii ) “What color? ”, (iii ) “How often applied? ” and (iv) “How many years have you used it? ” Our analyses also stratified the duration of use into 1–9 years, 10–19 years and 20 or more years according to the baseline report; duration was not allowed to advance during follow-up. Table I present s age-adjuste d deat h rates that are directly standardize d to the age distribution of person-year s among CPS-I participant s during the first 6 years of follow-up. Multivariate-adjuste d rate ratios were estimated by using Cox proportional hazards modeling, adjusting for age, race, cigarettes smoked per day (current smokers) or age at quitting (former smokers) , education and blue collar occupation. Multivariateadjusted deat h rates were derived by multiplying the adjusted ratio for each categor y of hair dye use by the age-standardized deat h rate for women who never used hair dye. Because cigarette smoking is an establishe d risk factor for bladder cancers among women4 and was associate d with hair dye use in our cohort (37% of ever smoker s used hair dye compared to 28% of never smokers) , we present results separatel y for lifelong nonsmokers. The deat h rate from bladder cancer was similar among women who reported ever using permanen t hair dye to that of never users, especially after multivariate adjustment (RR51.08, 95% CI 5 0.84–1.38) and in analyses restricted to lifelong nonsmoker s(RR50.92, 95% CI 5 0.61–1.40) . Among women who had used permanen t hair dyes, no consistent increase was seen in either the deat h rate from bladder cancer or the rate ratio associate d with hair dye use. While it is conceivabl e that use of permanen t hair dye might increase incidence, but not mortality, from bladder cancer , no association with incident bladder cancer was observed in a previous prospective study of registered nurses. 5 It may be prematur e to classify permanen t hair dye use as an important cause of bladder cancer among women. Nevertheless , the ongoing debat e about the safet y of hair dye illustrates the difficulty of accuratel y measuring and describing the smal risks that may or may not be associate d with these widely used consumer products. Yours sincerely, S. Jane HENLEY and Michael J. THUN