Objectives: The reported mutagenic and carcinogenic effects of some chemicals present in hair dyes have raised concern that hair dye use could increase breast cancer risk. This case-control study evaluated how detailed aspects of hair coloring and hair spray application by reproductive-age women may affect breast cancer risk. Methods: Cases were white female residents of three counties of western Washington state 45 years of age or less, who were diagnosed with breast cancer between 1983 and 1990 (n = 844). A sample of similarly aged women residing in the same counties served as controls (n = 960). Information on hair coloring and hair spray use, as well as other exposures, was ascertained during in-person interviews. Results: Breast cancer cases were slightly more likely than controls to report ever having used some type of hair coloring application, including use of rinses, semi-permanent or permanent dyes, as well as bleaching then dyeing or frosting their hair (relative risk [RR] = 1.3, 95% CI = 1.0-1.6, adjusted for age, fullterm pregnancies, family history of breast cancer, and weight). In subgroup analyses, women with exclusive use of just one of these methods of hair coloring application had no elevation in risk (similarly adjusted RR = 1.1, 95% CI = 0.9-1.3), whereas women who used two or more of these methods did have an elevated risk (RR = 1.9, 95% CI = 1.4-2.5). Hair spray use was not related to the risk of breast cancer (ever versus never users: RR = 1.0, 95% CI = 0.8-1.3). Conclusion: The lack of an association between exclusive use of a single type of hair coloring application and breast cancer risk argues that hair coloring application does not influence breast cancer risk among reproductive-age women. Thus, the results of the present study, as well as negative ones from most (but not all) prior studies, are most consistent with the conclusion that neither hair coloring application nor hair spray application influences breast cancer risk.
