Chemical Hair Relaxers and Straighteners (Formaldehyde, Lye/No-Lye, Uterine Cancer Association, Endocrine Disruption) — safety profile
High riskChemical hair relaxers and straightening treatments fall into two categories: lye-based (sodium hydroxide) or no-lye (calcium hydroxide/guanidine carbonate) relaxers that permanently break disulfide bonds, and keratin/Brazilian blowout treatments that use formaldehyde or formaldehyde-releasing chemicals (methylene glycol) to temporarily straighten hair through protein cross-linking.
What is this product?
Chemical hair relaxers and straightening treatments fall into two categories: lye-based (sodium hydroxide) or no-lye (calcium hydroxide/guanidine carbonate) relaxers that permanently break disulfide bonds, and keratin/Brazilian blowout treatments that use formaldehyde or formaldehyde-releasing chemicals (methylene glycol) to temporarily straighten hair through protein cross-linking. A landmark 2022 NIH study (Journal of the National Cancer Institute, Chang et al.) found that women who frequently used chemical hair straighteners had more than double the risk of uterine cancer compared to non-users (HR 2.55, 95% CI 1.46-4.45), with the association strongest among Black women who use relaxers at higher rates and from younger ages. FDA proposed banning formaldehyde in hair straightening products in 2023. Multiple endocrine-disrupting chemicals — phthalates, parabens, cyclosiloxanes — are common co-formulants.
What's in it
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Active Straightening Agent
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