Hair Straightening and Keratin Treatment (Formaldehyde/Methylene Glycol, Brazilian Blowout FDA Warning, CROWN Act, Relaxer Uterine Cancer Link) — safety profile
High riskHair straightening products encompass two distinct hazard categories: keratin smoothing treatments (which release formaldehyde when heat-activated) and chemical relaxers (which use sodium hydroxide or calcium hydroxide to break disulfide bonds).
What is this product?
Hair straightening products encompass two distinct hazard categories: keratin smoothing treatments (which release formaldehyde when heat-activated) and chemical relaxers (which use sodium hydroxide or calcium hydroxide to break disulfide bonds). The FDA issued a warning letter to Brazilian Blowout LLC in 2011 after OSHA testing found airborne formaldehyde levels of 0.08-5.4 ppm during application — exceeding the OSHA STEL of 2 ppm in some cases. Methylene glycol (the liquid form of formaldehyde) is listed on product labels as a formaldehyde alternative, but at flat-iron temperatures (230C/450F) it decomposes to release formaldehyde gas. A 2022 NIH Sister Study landmark finding: women who used chemical hair straightening products more than 4 times per year had more than double the risk of uterine cancer (HR 2.55, 95% CI 1.46-4.45) compared to non-users. This study (JNCI, 2022) analyzed 33,497 women over 11 years. The EPA and CPSC have not regulated formaldehyde content in hair smoothing products specifically. The EU Cosmetics Regulation 1223/2009 limits formaldehyde to 0.2% (as free formaldehyde) in cosmetic products, with mandatory labeling above 0.05%.
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