The short answer
A large NIH study found that women who frequently used chemical hair straighteners or relaxers had a higher risk of uterine cancer than those who did not. This is an observed association, not proof that the products cause cancer, and the overall risk remained low. Research is ongoing.
A large NIH study linked frequent relaxer use to higher uterine cancer risk.
This is an observed association, not proof of cause and effect.
The overall risk of uterine cancer still remained low.
Frequent use — not occasional use — was the pattern studied.
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The claim
News reports and lawsuits have pushed the claim that chemical hair straighteners and relaxers cause cancer, above all uterine cancer. Attention grew after a large U.S. government study reported a link. The concern falls hardest on Black women, who use these products more often.
What the study found
The study was the NIH-funded Sister Study. It followed 33,497 women for about 11 years, and 378 of them developed uterine cancer. Women who used chemical straighteners or relaxers often, meaning more than four times in the past year, were more than twice as likely to develop uterine cancer as women who did not use them.
The actual numbers help here. Among women who never used hair straighteners, an estimated 1.64 in 100 would develop uterine cancer by age 70. Among frequent users, the estimate was 4.05 in 100. That is a real jump, but the risk stays low for most people.
What it does and does not prove
A study like this can show an association. On its own it cannot prove the products cause cancer, because users and non-users differ in other ways too. Researchers have named chemicals found in some straighteners as a plausible route, including parabens, bisphenol A, metals and formaldehyde. Scalp burns and sores from these treatments may let more of a chemical through the skin. More research is underway.
About 60 percent of the women in the study who reported recent straightener use were Black. The link did not differ by race in the numbers. But Black women use these products more often, and start younger, so the finding matters most to them.
The bottom line
Frequent use of chemical hair straighteners is linked to a higher rate of uterine cancer in a large, credible study. That is not yet proof of cause, and the overall risk stays low. Ask your care team whether your own use is worth discussing.
When to get help sooner
- Call 911 or go to an emergency department if you have very heavy vaginal bleeding, or you feel faint, dizzy or short of breath along with bleeding. Do not drive yourself.
- Call your care team the same day if you have any vaginal bleeding after menopause, even a small amount of spotting.
- Call your care team within a day or two if you have bleeding or discharge between periods, pelvic pain, pain during sex, or pain when you urinate. These have many causes besides cancer, but they should be checked.
Sources
Common questions
Do hair relaxers cause cancer?
A large study links frequent use to higher uterine cancer risk, but this is an association, not proof of cause and effect. The overall risk remained low.
How much use did the study look at?
The higher risk was seen in women who used these products frequently, defined as more than four times in the previous year, compared with women who did not use them.
Should I stop using relaxers?
The NIH study did not tell people to stop. Ask your care team whether your own use or risk factors are worth discussing.
Who is most affected by this concern?
Black women use these products more often, so the concern falls hardest on them, which makes the research especially important.
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Sources last checked: 2026-07-13 what this meansLast updated: 2026-10-01Next planned review: 2027-01-13
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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