Hair Relaxers and Your Health: What the Research Says

TL;DR: A large US study found that women who used hair straighteners or relaxers often had a higher rate of womb (uterine) cancer than women who never used them, but the overall risk stayed low and the study shows a link, not proof of cause. Results from other studies are mixed. You do not need to feel guilty about your hair. You can lower exposure by relaxing less often, protecting your scalp, and checking labels for formaldehyde, and you should see a doctor about any bleeding after menopause or unusual bleeding between periods.

If you grew up in Lagos, Accra or Nairobi, or in a Black household in London or Birmingham, the relaxer was probably part of growing up. The tingle at the scalp, the timer on the counter, the aunty who told you to sit still. So when headlines in 2022 said hair straighteners might be linked to womb cancer, many of us felt a jolt of worry, and some of us felt judged. This post walks through what the research found, what it cannot tell us, and what you can do with that information, without anyone telling you how to wear your hair.

What did the 2022 Sister Study find?

It found that women who had used hair straightening products in the past year had a higher rate of uterine cancer over the following decade than women who had not, with the strongest link in frequent users. It was the first study to look at this question.

The study, led by researchers at the US National Institute of Environmental Health Sciences and published in the Journal of the National Cancer Institute, followed 33,947 women aged 35 to 74 who still had a uterus. Over an average of 10.9 years, 378 of them developed uterine cancer. Women who reported any straightener, relaxer or pressing product use in the previous 12 months had about 1.8 times the rate of uterine cancer, and women who used them more than four times a year had about 2.55 times the rate, compared with never users. Hair dyes and perms were not linked to uterine cancer.

In everyday numbers, the researchers estimated that about 1.64 percent of never users would develop uterine cancer by age 70, compared with about 4 percent of frequent users. So the risk rose, but most frequent users in the study did not develop cancer.

There is an important detail for us. Only about 7.4 percent of the women in the study were Black. The authors noted that the findings could matter more for Black women because they tend to use these products more often, start younger, and may use harsher formulations, and they called for more research in Black women specifically.

What have other studies found since?

The picture is mixed, which is normal in science. A 2023 study of 44,798 Black women in the Black Women's Health Study found no clear overall link between heavy, long-term relaxer use and uterine cancer. When the researchers looked only at women after menopause, though, long-term heavy use and 20 or more years of use were linked to a higher risk. There was no link in women before menopause.

The same research group behind the Black Women's Health Study had earlier reported that relaxer use was linked to a modestly higher rate of fibroids, which they described as a hypothesis worth testing rather than a proven cause. If fibroids are part of your story, we cover them in our uterine fibroids guide.

A 2026 follow-up of Sister Study participants, also in the Journal of the National Cancer Institute, looked at cancers outside the reproductive system. It reported possible links with thyroid cancer, non-Hodgkin lymphoma and pancreatic cancer, saw little sign that risk climbed with more frequent use, and said more research is needed to confirm the findings.

Association or cause: what is the difference?

An association means two things show up together more often than chance would suggest. A cause means one thing makes the other happen. These studies show associations.

Here is why that matters. Women in these studies reported their own hair product use, sometimes years before a diagnosis, so memories can be imperfect. Women who relax often may differ from women who do not in other ways, such as income, other products they use, or access to healthcare, and researchers can adjust for some of these differences but never all of them. None of these studies measured the exact chemicals in the products women used. The 2022 study's own conclusion was that its findings need to be repeated in other settings and that the specific chemicals behind the link still need to be identified.

The researchers do point to plausible reasons for concern. Hair products can contain chemicals that disrupt hormones or are linked to cancer, and the womb lining is sensitive to hormones. A plausible mechanism plus a link seen in some studies is a good reason to keep studying, and a fair reason to cut back if you want to. It is not a reason to panic about the relaxers you have already had.

Where do formaldehyde rules stand?

The formaldehyde warnings from the US Food and Drug Administration are about hair smoothing and keratin-style treatments, which are not the same as a classic relaxer. The FDA says many hair smoothing products contain formaldehyde, also listed as formalin or methylene glycol, which is released as a gas when the hair is heated. It can irritate the eyes, nose, throat and skin, and the International Agency for Research on Cancer classifies formaldehyde as a human carcinogen at high or prolonged exposure.

You may have read that the FDA planned to ban formaldehyde in hair straightening products. As of October 2026, that ban has not been finalised. The FDA's cosmetics news and updates page lists no final rule on it, and the agency's consumer page still tells people to read labels and ask their salon about ingredients. Rules in Nigeria, Kenya, Ghana, South Africa and the UK are set by each country's own regulators, so check with yours if you want to know what applies where you live.

Practical choices that respect your hair

How you wear your hair is your decision, shaped by work, cost, time, culture and what makes you feel like yourself. Wearing your hair natural is not a duty, and relaxed hair is not a moral failing. If you want to lower your exposure, here are options drawn from FDA safety advice for relaxers and the research above:

• Stretch the time between touch-ups. The strongest links were in women who used straighteners more than four times a year.
• Protect your scalp. Avoid putting relaxer directly on the scalp, do not scratch or brush your scalp for three days before, and skip relaxing if your scalp is irritated or broken.
• Follow timing exactly. Use a timer, never leave the product on longer than the directions say, wear gloves, and rinse well.
• Read labels for formaldehyde, formalin or methylene glycol, especially on smoothing or keratin treatments, and ask your stylist what they are using.
• Ask about ventilation if you have heat-based smoothing done in a salon.
• Consider protective styles or longer breaks if they suit your life, keeping in mind that tight styles can bring their own problems. Our post on hair loss in Black women explains traction alopecia and when tenderness or burning needs a dermatologist.

If you have burns, scabs, hair loss or another reaction after a relaxer, tell your doctor or a pharmacist, and stop using that product.

Which symptoms should you never ignore?

See a doctor promptly if you have any bleeding or spotting after menopause, heavy periods that are unusual for you, bleeding between periods, or a change in your vaginal discharge. The NHS lists these as the main symptoms of womb cancer, and says to get them checked without waiting.

These symptoms are common and usually have other causes, but finding womb cancer early makes it easier to treat. Bleeding after menopause always deserves a check. We go into more detail in womb cancer: the signs to know. If you are worried you will be brushed off, our guide to talking to your gynaecologist so you are not dismissed can help.

Bringing it back to you

The research on relaxers is still developing, and the women most affected have been under-studied. What we know is enough to make informed choices, and not enough to justify fear or shame.

If you want to keep track, Asele's symptom logging lets you note unusual bleeding, spotting or discharge alongside your cycle, and the Health Brief turns those notes into a summary you can take to your appointment. Amara can talk you through what you have read in Yoruba, Hausa, Igbo, Swahili, French or English. You can find us at Asele.

This post is education, not medical advice. If you have symptoms or questions about your own risk, please speak to a clinician who can examine you.

References

1. Chang CJ, et al. Use of Straighteners and Other Hair Products and Incident Uterine Cancer. J Natl Cancer Inst. 2022. pubmed.ncbi.nlm.nih.gov (full text: pmc.ncbi.nlm.nih.gov)
2. Bertrand KA, et al. Hair relaxer use and risk of uterine cancer in the Black Women's Health Study. Environ Res. 2023. pubmed.ncbi.nlm.nih.gov
3. Wise LA, et al. Hair relaxer use and risk of uterine leiomyomata in African-American women. Am J Epidemiol. 2012. pubmed.ncbi.nlm.nih.gov
4. Bailey JT, et al. Use of hair straighteners and chemical relaxers and incidence of non-reproductive cancers. J Natl Cancer Inst. 2026. pubmed.ncbi.nlm.nih.gov
5. US Food and Drug Administration. Hair Smoothing Products That Release Formaldehyde When Heated. fda.gov
6. US Food and Drug Administration. Cosmetics News and Events. fda.gov
7. US Food and Drug Administration. Hair Dyes and Relaxers: Tips to Keep You Safe. fda.gov
8. NHS. Symptoms of womb (uterus) cancer. nhs.uk