The presence of formaldehyde, a carcinogen in hair treatments such as keratin and Brazilian blowouts (a chemical treatment for temporarily straightening hair that originated in Brazil and has gained widespread popularity), has long been a concern for experts, given the potential for it to escape as a gas when exposed to heat, a phenomenon known as "off-gassing." Repeated inhalation of these fumes can cause eye and respiratory irritation and sometimes increase the risk of head and neck cancer, especially in poorly ventilated areas.
Researchers from Emory University in Georgia analyzed data from 46,287 American women participating in a long-term study, the Sisters Project. The women, aged 35 to 74, had no personal history of breast cancer but at least one sister diagnosed with the disease. Participants were followed for an average of 13.1 years, and their use of hair straighteners and relaxers in the 12 months prior to joining the study was assessed.
Pancreatic cancer: The risk increased by 166% in women who used hair straighteners.
Thyroid cancer: 71% increased risk.
Non-Hodgkin lymphoma: 62% increased risk.
The risk is higher among frequent users, those who use the products more than four times a year, whose risk of developing pancreatic cancer more than doubles.
The study showed that the use of hair straighteners varies by race:66% of black women.
25% of women are of Hispanic/Latina origin.
Only 1.3% of non-Hispanic white women.
The European Union and at least 10 US states have banned or proposed bans of formaldehyde and its precursors in personal care products.
The FDA proposed a national ban on these substances in 2023, but it has not yet been enacted.
Some states have begun banning formaldehyde in all cosmetics, with Washington being the latest to do so.
Under the Toxic-Free Cosmetics Act, all formaldehyde-releasing chemicals will be banned starting January 1, 2027, with retailers allowed to sell existing stock until that date.
The study highlights the long-term health risks of chemical hair treatments, particularly among frequent users, and calls for further research and regulation to limit exposure to carcinogens.
The study was published in the Journal of the National Cancer Institute.
