Sodium Hydroxide. *From Lactic Acid.

Sodium hydroxide lye relaxers operate at pH 12–14, swelling the cuticle and allowing hydroxide ion to penetrate the cortex where it breaks disulfide bonds via lanthionization—a permanent, irreversible chemical change. Extreme alkalinity causes chemical burns and scalp lesions that significantly enhance percutaneous absorption of co-formulants. NIEHS Sister Study (2022) found HR 2.55 for uterine cancer in frequent users. JNCI 2026 follow-up found HR 2.66 for pancreatic cancer, HR 1.71 for thyroid cancer, and HR 1.62 for non-Hodgkin's lymphoma. Epidemiological signal is strong; causal pathway likely includes co-formulant absorption (formaldehyde-releasers, parabens, phthalates, BPA, metals) through burn-damaged scalp. Disproportionate risk burden on Black and African American women, many starting use in childhood/adolescence. EU Annex III restricts concentration and mandates professional use for higher-concentration products.

Permitted in hair relaxer formulations as active at pH 12–14. NIEHS Sister Study (2022, EPH) found women using chemical straighteners ≥4x/year faced HR 2.55 for uterine cancer. JNCI 2026 follow-up linked frequent use to pancreatic cancer (HR 2.66), thyroid cancer (HR 1.71), and NHL (HR 1.62). FDA has not yet issued a formal ban but cancer findings have triggered significant regulatory and litigation scrutiny.