Relationship of hair dye use, benign breast disease, and breast cancer.

An epidemiologic case-control study of 118 breast cancer patients and 233 controls was conducted to test the hypothesis that hair dyes are related to breast cancer. Matched controls were selected by "random digit dialing," and all epidemiologic data were collected by telephone interviews. No overall association was detected. On a prospective basis, the interaction between hair dye exposure and six variables known to be risk factors for breast cancer then were examined: previous benign breast disease (BBD), "ever" versus "never" pregnant, age at first pregnancy, menopause induced by operation, age at menarche, and education. A statistically significant increased risk of breast cancer was found for women with a history of BBD and exposure to hair dyes as compared to women with BBD but no hair dye exposure: The relative risk (RR) was 4.5, and the 95% confidence intervals (C) were 1.20 and 15.78. A total of 24 women (19 patients and 5 controls) reported a history of BBD and hair dye use. Further analysis revealed a significant association between hair dye use and breast cancer among women 40-49 years of age (RR = 3.33; 95% CI: 1.1 and 10.85) and a highly significant (P = 0.0008) dose-response relationship among women who used hair dyes for changing their natural color as opposed to covering gray hair. The numbers of patients and controls included in this study were small and several hypotheses were tested. Additional epidemiologic studies are needed before firm conclusions can be reached concerning the nature of these associations.