Swedish researchers have found that, while aromatic amines classified as carcinogens have been prohibited from use in cosmetics in the European Union, several have been measured in the blood of hairdressers and the concentrations increase significantly with the frequency of light-color permanent hair dye and hair waving treatments. Gabriella Johansson, et al., “Exposure of hairdressers to ortho- and meta-toluidine in hair dyes,” Occupational & Environmental Medicine, June 9, 2014.

The researchers measured eight potentially carcinogenic aromatic amines in the blood of 295 hairdressers, 32 users of hair dyes and 60 controls. All were non-smoking women. According to the study, “A comparison of the adduct concentrations found in hairdressers, consumers and controls showed no statistically significant differences,” but for hairdressers, o- and m-toluidine concentrations increased with the number of dye and waving treatments performed each week. The researchers recommend that future studies focus on “finding exposure sources of o- and m-toluidine in products used by hairdressers” who are at an excess risk for urinary bladder cancer, which has purportedly been associated with these chemical exposures.