Hair dyes and risk of glioma among Nebraska women.

The etiology of brain cancer is not well understood. We conducted a population-based case-control study among 112 white women in Nebraska who were newly diagnosed with glioma between July 1988 and June 1993, and 215 controls, to identify risk factors for this disease. A 1.7-fold increased risk of glioma was observed for women who ever used hair coloring products (95% confidence interval (CI) = 1.0-2.9, 62 cases), and a 2.4-fold risk for those who used permanent hair coloring products (odds ratio (OR) = 2.4, 95% CI = 1.3-4.5, 39 cases). For women with the most aggressive form of glioma, glioblastoma multiforme, risk increased with duration of exposure to 4.9 (95% CI = 1.6-15.7, 10 cases) after 21 or more years of permanent hair coloring use. Higher risks were observed with earlier age at first use, but we did not see an exposure-response pattern with frequency of use of permanent dyes. No association was observed with use of non-permanent (sometimes called temporary or semi-permanent) hair coloring products. These suggestive findings need confirmation in future studies with larger sample sizes, fewer proxy respondents, and the ability to evaluate the effect of changes in formulations over time.