Hair dyes often contain harsh chemicals that raise questions about cancer risk. A landmark study tracked over 120,000 women for 36 years to uncover the facts.
In the US and Europe, about 80% of commercial hair colors are oxidative permanent dyes. These rely on hydrogen peroxide to break down hair's natural melanin and deposit synthetic pigments, sometimes including compounds like o-Phenylenediamine.
Such ingredients are classified as probable human carcinogens by the International Agency for Research on Cancer (IARC), as noted in their February 24, 2020 press release. Yet, few studies have examined health risks for users.
Researchers at Boston University School of Public Health conducted a prospective observational study from 1976 to 2012, following 120,000 US nurses aged 30-55. Participants completed questionnaires every two to four years detailing their hair dye use.
Participants were grouped as non-users or those who had used hair dye at least once, regardless of frequency. They reported any doctor-confirmed cancers.
Overall, hair dye users showed no elevated risk for sarcomas, carcinomas, or cancer-related mortality. However, permanent dye users—and those dyeing to lighter shades—faced higher basal cell carcinoma risk. Frequent use was also associated with increased breast cancer risk.
Importantly, these are associations, not causal links. The study, primarily involving white brunettes who were US nurses, may not generalize globally. It also didn't account for family history or environmental factors.
