Hair Relaxer Cancer Lawsuits: Uterine Cancer Claims Against L'Oréal and Others

An NIH Study, 40,000 Lawsuits, and a Community Disproportionately Affected

In October 2022, the National Institutes of Health published a study in the Journal of the National Cancer Institute finding that women who used chemical hair straighteners more than four times per year had more than twice the risk of developing uterine cancer compared to non-users — a relative risk of 2.55. Within months, attorneys filed thousands of lawsuits against manufacturers including L'Oréal, Revlon, Soft Sheen-Carson, and others. By early 2024, a federal multidistrict litigation (MDL) in the Northern District of Illinois had consolidated more than 8,500 cases, with projections reaching 40,000 or more. Because hair relaxers are used at substantially higher rates by Black women — the population at greatest risk — the litigation carries significant environmental justice dimensions alongside its tort law mechanics.

Uterine cancer is the most common gynecological cancer in the United States, with approximately 65,000 new cases diagnosed annually. The question of how much chemical hair products contribute to that burden is now central to one of the fastest-growing mass tort litigations in the country.

The Scientific Foundation: The Sister Study

The key study driving the litigation — "Use of Straighteners and Other Hair Products and Incident Uterine Cancer" by Chang et al. (2022) — analyzed data from the NIH Sister Study, a prospective cohort of 33,947 U.S. women aged 35–74. Researchers tracked self-reported use of hair straighteners, perms, relaxers, and highlights over an 11-year follow-up period and recorded uterine cancer diagnoses.

Key findings:

• Women who used straighteners in the past 12 months had 1.8 times the uterine cancer risk of non-users.
• Frequent users (4+ times per year) had 2.55 times the risk — surpassing the 2.0 threshold often cited in toxic tort causation analysis.
• The association was strongest for uterine cancer specifically; limited associations were found for ovarian cancer.
• The researchers proposed endocrine-disrupting chemicals in straighteners — including phthalates, parabens, bisphenol A, and formaldehyde-releasing agents — as the biological mechanism.

Why the Products Are Chemically Distinct

Chemical hair relaxers work differently from coloring or perming products. They typically contain sodium hydroxide (lye) or guanidine carbonate (no-lye), which permanently alter the protein structure of hair. The process often involves heated application to the scalp, where broken skin and heat-enhanced absorption may increase chemical uptake. Independent testing by organizations including the Environmental Working Group has detected multiple endocrine-disrupting compounds in popular relaxer formulations that are not fully disclosed on product labels because cosmetic manufacturers are not required under the Federal Food, Drug, and Cosmetic Act to pre-approve ingredients.

Defendants Named in the MDL

Revlon's 2022 bankruptcy complicated its inclusion as a defendant. Courts must navigate how mass tort claims interact with bankruptcy proceedings — a recurring challenge seen also in the Purdue Pharma and Fruit of the Loom asbestos cases.

Causation Challenges and Defense Arguments

Defendants have signaled several lines of scientific attack:

• Recall bias: The Sister Study relied on self-reported use over a 12-month window preceding study enrollment, creating potential for imprecise exposure measurement.
• Confounding factors: Heavy relaxer users may have other correlated lifestyle, dietary, or hormonal risk factors for uterine cancer.
• Single study limitation: As of 2024, the Chang et al. paper is the primary epidemiological evidence; replication in independent cohorts has not yet occurred.
• Specific product identification: Plaintiffs must identify which brand and formulation they used — difficult for products used intermittently over decades.

What Plaintiffs Must Prove

• Regular use of chemical hair straightener or relaxer products for an extended period (typically years to decades).
• Diagnosis of uterine cancer, uterine fibroids, or other alleged conditions.
• Identification of specific defendant's product used by the plaintiff.
• Expert testimony establishing general and specific causation linking endocrine-disrupting chemicals to the diagnosed condition.

The MDL is in the early stages as of 2024. Bellwether trials — small sets of representative cases tried first to assess how juries respond — will likely begin in 2025 and heavily influence settlement negotiations.

This article is for informational purposes only and does not constitute legal advice.