Case-control study of hair dye use by patients with breast cancer and endometrial cancer.

A case-control study was undertaken of use of permanent and semipermanent hair dyes by women with cancers of several sites, including breast and endometrium. In London, Ontario, 50 cases of of breast cancer and in Toronto 35 cases of breast cancer and 36 cases of endometrial cancer were identified in cancer treatment centers. In London, controls were selected from hospitalized women with diseases other than cancer; in Toronto, controls were selected from women living in the same neighborhood as the patients with cancer. The results did not suggest an increased risk of either breast or endometrial cancer in users of permanent or permanent and semipermanent dyes combined. Although the numbers of cases and controls were small, the consistency of the results for both sites, in both study centers, and the absence of any clear positive relationship between various measures of intensity of use and risk of cancer provided evidence that a large increase in risk was not missed.