Published: March 20, 2026 · Updated: March 2026

Chemical Hair Straightener Uterine Cancer Link: The Scientific Evidence

Last updated: March 2026

Millions of women — particularly Black women — used chemical hair straighteners for years, even decades. Many never imagined the products in their bathroom could be connected to a cancer diagnosis. Now the science says they were wrong to feel safe.

This page explains what the research found, which chemicals are the problem, and what it means for women who have been diagnosed with uterine cancer.

The study that changed everything

In October 2022, researchers from the National Institutes of Health (NIH) published a landmark study in the Journal of the National Cancer Institute. The study was part of the Sister Study — one of the largest long-term health studies of American women ever conducted.

The researchers tracked 33,947 women between the ages of 35 and 74 for an average of nearly 11 years. They tracked cancer rates and asked detailed questions about health habits — including hair product use.

The finding that made headlines:

Lead author Dr. Alexandra White of the NIH National Institute of Environmental Health Sciences (NIEHS) noted that the findings were "concerning" and warranted further investigation, but emphasized that the results were consistent across different analyses.

What Chemicals Are We Talking About?

Chemical hair relaxers work by breaking down the protein bonds in hair strands — that's what makes curly hair temporarily straight. But the chemicals that do this job don't stay on the hair alone. They absorb through the scalp, especially when heat is applied or when the scalp has small cuts or irritation from the relaxer itself (which is common).

The chemicals most linked to cancer risk include:

Phthalates

Phthalates are plasticizer chemicals used in many cosmetic products. They are classified as endocrine disruptors — meaning they interfere with the body's hormone systems. In particular, phthalates mimic estrogen. Uterine cancer (also called endometrial cancer) is a hormone-sensitive cancer, meaning it grows in response to estrogen. Anything that artificially raises estrogen exposure can increase cancer risk.

Phthalates have been detected in hair relaxer products at high levels. A 2021 lab analysis found that hair products marketed to Black women contained significantly higher concentrations of endocrine-disrupting chemicals than products marketed to the general population.

Parabens

Parabens are preservatives used to extend the shelf life of cosmetic and personal care products. Like phthalates, parabens are estrogen mimics. They can bind to estrogen receptors in the body and trigger the same biological responses as natural estrogen — potentially feeding hormone-sensitive cancers like uterine cancer.

Formaldehyde and Formaldehyde-Releasing Chemicals

Some hair straightening products — especially keratin treatments and certain relaxers — contain formaldehyde or chemicals that release formaldehyde during use. Formaldehyde is a known human carcinogen. It has been linked to leukemia and other cancers. The International Agency for Research on Cancer (IARC) classifies formaldehyde as Group 1: definitively carcinogenic to humans.

Cyclosiloxanes (D4 and D5)

These silicone-based chemicals are used to make hair products feel smooth. Research has linked cyclosiloxanes to endocrine disruption and has raised concern about their effects on the uterus specifically. The European Union has restricted D4 and D5 in cosmetics due to environmental and health concerns.

Lye and Chemical Relaxer Bases

The active straightening agents — sodium hydroxide (lye) in traditional relaxers, or guanidine carbonate in "no-lye" versions — are highly caustic. They cause scalp irritation, chemical burns, and open wounds that allow other chemicals in the product to enter the bloodstream more easily.

Why are Black women disproportionately affected?

Research consistently shows that Black women use chemical hair relaxers at far higher rates than women of other racial groups — and they typically start younger. A 2019 survey found that approximately 60% of Black women in the U.S. had used chemical hair straighteners, compared to around 12% of white women.

Many Black women started using relaxers as children — sometimes at age 5 or 6 — because relaxed hair was treated as more professional or acceptable. That means decades of cumulative chemical exposure, often starting before the body is fully developed.

That part is hard to sit with.

The NIH Sister Study confirmed this disparity. Researchers noted that because Black women use hair relaxers at much higher rates than other groups, they likely face higher levels of exposure to the associated chemicals.

Uterine cancer rates are also already higher in Black women than in white women. The combination of higher baseline cancer risk and higher chemical exposure creates a compounded health burden.

What Cancers and Conditions Are Linked?

The NIH study focused on uterine cancer, but other research has examined related conditions. Here is what the current evidence suggests:

• Uterine (endometrial) cancer: Strongest evidence; 2.55x increased risk in frequent users
• Ovarian cancer: A 2022 study in Cancer Prevention Research found elevated ovarian cancer risk in women who straightened their hair
• Uterine fibroids: Multiple studies have found higher rates of fibroid diagnoses in women who use hair relaxers regularly
• Endometriosis: Early research suggests a possible link, though the evidence is less definitive than for uterine cancer
• Breast cancer: Under active investigation; some research suggests a possible link but findings are mixed

Did Companies Know?

Plaintiffs in MDL 3060 allege that chemical hair relaxer manufacturers were aware of the risks associated with their products' ingredients and failed to disclose them to consumers. Internal documents and research cited in lawsuits suggest that companies conducted or were aware of safety studies on these ingredients for years.

The manufacturers — L'Oréal, Revlon, Namaste Laboratories, Strength of Nature, and others — dispute these claims and maintain that their products are safe when used as directed.

Judge Rowland's 2024 decision to allow punitive damages suggests the court found sufficient evidence of potential corporate wrongdoing to let that issue go to a jury.

What Should You Do If You Have Been Diagnosed?

If you used chemical hair relaxers regularly and have been diagnosed with uterine cancer, ovarian cancer, endometriosis, or uterine fibroids, you should know that you have legal options. Thousands of women have already filed claims in MDL 3060.

There are time limits — statutes of limitations — that apply. In many states, you have 2–3 years from the date of diagnosis (or from the date you learned about the hair relaxer connection) to file a lawsuit. Every month of delay makes it harder to meet this deadline.

Find out if you qualify for a hair relaxer cancer claim →

Sources

• Chang CJ, et al. "Use of Straighteners and Other Hair Products and Incident Uterine Cancer." Journal of the National Cancer Institute, 2022.
• Zota AR, et al. "Chemicals in hair products used by Black women." Environmental Health Perspectives, 2021.
• White AJ, et al. "Hair product use and ovarian cancer risk." Cancer Prevention Research, 2022.
• International Agency for Research on Cancer (IARC). Formaldehyde classification, 2012.
• National Institute of Environmental Health Sciences, Sister Study, 2022.