Permanent Hair Dye

The Sister Study, a prospective cohort study of 45,000 women, found an increased risk of breast cancer associated with permanent hair dye use. Chemicals in hair dye applied to the scalp can pass directly into the bloodstream due to the scalp's high vascular density. The permanent hair-dye industry uses over 5,000 different chemicals, some of which are known carcinogens. The Sister Study found an increased risk of bladder cancer associated with permanent hair dye use. Many hair dye chemicals are classified as endocrine disruptors that interfere with hormone signalling.