Do Relaxers Cause Cancer? Why How Often You Relax Matters

No study has shown that hair relaxers cause cancer, but frequent use is linked to a higher risk of uterine cancer. The breast cancer link is weaker and the studies disagree.

In absolute terms, the gap is real but small. The NIH's Sister Study estimated that about 4 in 100 frequent users would develop uterine cancer by age 70. For women who never used straighteners, it was about 1.6 in 100.

If you've had a touch-up every eight weeks since you were a teenager, those headlines probably landed hard. You may be deciding whether to book the next appointment, stretch it out or grow it out. The detail that matters most for that decision is how often, and most coverage skips it.

What the Uterine Cancer Studies Found

Two big US studies point the same way, with different women in them. The first is the NIH's Sister Study. Researchers followed nearly 34,000 women aged 35 to 74 for close to 11 years, and 378 of them developed uterine cancer.

Women who straightened more than four times in the past year had about 2.5 times the uterine cancer rate of women who never did. Women who straightened four times or fewer had a slightly higher rate, but that result was small enough to be chance. The pattern climbed with frequency, which is part of why the finding is taken seriously.

Now the absolute numbers. The NIH estimated that 1.64% of women who never used hair straighteners would develop uterine cancer by 70. For frequent users, that rose to 4.05%. That's about 2 or 3 more cases for every 100 women who relax often, if the link is causal.

The NIH notes that uterine cancer makes up about 3% of new cancer cases. Rates have been rising in the US, particularly among Black women. About 60% of the women who had used straighteners in the past year were Black.

The second study looked only at Black women. In 2023, Boston University's Black Women's Health Study reported on nearly 45,000 Black women followed for up to 22 years. After menopause, long-term heavy relaxer use was linked to about a 60% to 70% higher uterine cancer risk. Before menopause there was no clear link.

Who Was in These Studies, and Why It Matters

The Sister Study isn't a random sample of American women. Everyone in it was free of breast cancer when they joined, between 2003 and 2009. And every one of them had a sister who'd been diagnosed with it. That makes it a group with a family history, recruited to study breast cancer, not uterine cancer.

Most of the women were white. The link didn't differ significantly by race, but the estimate for Black women was wide and could have been no increase at all.

Twenty-six uterine cancers among frequent users is a small number to build a lifetime estimate on. Women also reported their own use for one 12-month window, and nobody recorded brands or ingredients. Formulas may also have changed over time, which the researchers point out themselves.

That's where the Black Women's Health Study helps. It's all Black women, it ran for decades, and it found a link after menopause, though not before menopause or across all women combined. Two different groups of women, studied in different ways, landing in a similar place is stronger evidence than either study alone.

Do Relaxers Cause Breast Cancer?

The evidence doesn't show that relaxers cause breast cancer, and the two main studies don't agree. The earlier one came from the Sister Study in 2019 and used data from 46,709 women. Women who straightened at least every five to eight weeks were about 30% more likely to develop breast cancer.

A 2021 Black Women's Health Study paper looked at the same question in 50,543 Black women followed for an average of almost 18 years. Ninety-five percent of them had used relaxers, and 2,311 developed breast cancer. Overall, the authors called the results largely null.

One group stood out. Women who used lye relaxers at least seven times a year, for 15 years or more, had a higher risk of one type. Their risk of estrogen receptor positive breast cancer was about 32% higher. But that estimate could plausibly have been no increase at all, and the authors said consistent results from several studies were still needed.

So for breast cancer, the honest answer is maybe, and probably small if it's there. That's a less dramatic answer than most headlines give.

Does Hair Relaxer Cause Ovarian Cancer or Other Cancers?

A 2021 Sister Study analysis of 40,559 women found 241 ovarian cancers over about 10 years. Frequent straightener use, more than four times a year, was linked to about double the risk. Any use at all wasn't clearly linked. It's a single study, so treat it as a signal rather than an answer.

The newest follow-up, published in September 2025, looked beyond reproductive cancers. Among 46,287 Sister Study women followed for a median of 13 years, straightener use was linked to more thyroid and pancreatic cancer. A link with non-Hodgkin lymphoma was possible but not clear.

The case numbers behind those findings are tiny. Only 12 straightener users developed pancreatic cancer, and 22 developed thyroid cancer. Risk didn't climb neatly with more frequent use, and among Black women the study had too few cases to say much. The authors called for confirmation before anyone treats these as established.

Is the FDA Banning Hair Relaxers?

Not yet, and the proposal on the table is narrower than many people think. As of mid-November 2026, the FDA hasn't published its proposed ban. Its current federal regulatory agenda lists the proposal for November 2026, still at the proposed rule stage. The FDA's spring 2023 agenda had aimed for April 2024.

The proposal would prohibit formaldehyde and formaldehyde-releasing chemicals, such as methylene glycol, in hair smoothing and straightening products that are applied to the hair and heated. Heat is the point. The FDA says that when these solutions are heated, formaldehyde is released into the air as a gas. You and your stylist then breathe it in.

A cream relaxer that goes on, gets timed and is rinsed out without heat isn't what that rule describes. That doesn't clear relaxers. The NIH lists parabens, bisphenol A, metals and formaldehyde among the chemicals found in straighteners. Nobody yet knows which one, if any, explains the cancer link.

For any smoothing or straightening product you're considering, the FDA says to check the label for three names:

• formaldehyde
• formalin
• methylene glycol

If a retail product has no ingredient list, the FDA recommends not buying it. In a salon, it suggests that if your stylist isn't sure whether formaldehyde is in the product, you may not want to use it.

What Is Still Unknown

Quite a lot, and the gaps matter for your decision. Nobody knows which chemical is responsible, or whether it's one ingredient, a mixture or something about how often the scalp is exposed.

The Sister Study can't say whether lye and no-lye relaxers differ. Its 2025 paper says the questionnaire didn't ask which type women used. Its exposure was also a single 12-month window, used as a stand-in for years of habits.

And these studies measured use, not stopping. So they can't tell you how fast any extra risk fades once you quit.

Keep Relaxing, Cut Back or Go Natural?

No study has tested any of the options below. This is practical guidance built from what the studies measured, so treat it that way.

The number to watch is how often. In the Sister Study, the clear rise in uterine cancer was in women who straightened more than four times a year. The American Academy of Dermatology advises that touch-ups should only be done every two to three months, only on new growth, and by a professional.

That spacing lands right at the study's line. A touch-up every eight weeks works out to about six a year, which counts as frequent. Every three months is four a year, the group whose risk wasn't clearly raised, though the study couldn't rule out a smaller increase.

Protect your scalp. The 2022 study authors suggest that straighteners can cause scalp lesions and burns, which may let chemicals through more easily. They add that scalp skin has absorbed more than forearm skin in earlier studies.

• Don't relax over a scalp that's scratched, sore, flaking or broken anywhere.
• Tell your stylist the moment it stings, rather than sitting through the burn for straighter results.
• If it burns, ask for the relaxer to be rinsed out straight away.
• Ask what's in the product, especially before any treatment that's sealed in with a flat iron.

If you'd rather stop altogether, you don't have to big chop. Transitioning month by month without breakage covers how to grow it out while the relaxed ends are still there. If you're keeping your relaxer, the care that relaxed hair needs between touch-ups matters more once you start stretching them.

Cutting back isn't a failure of nerve. Going from every six weeks to every three months cuts your applications by more than half. That's the change that lines up best with how the risk showed up in the data.

When to See a Doctor

Don't wave off the symptoms of uterine cancer, especially if you've relaxed often for years. MedlinePlus lists bleeding between periods or after menopause as a sign of endometrial cancer, which starts in the lining of the uterus.

It also lists long, heavy or frequent bleeding after 40, and lower belly pain or pelvic cramping. MedlinePlus advises seeing a provider for any bleeding or spotting after menopause, bleeding that lasts longer than 7 days, or new discharge after menopause. Mention your relaxer history when you go.

Keep up with regular breast screening, and get any new breast lump checked, whatever your relaxer history.

For your scalp, see a board-certified dermatologist if a burn doesn't heal, or if you notice any thinning. Thinning edges have their own set of causes worth ruling out.

Frequently Asked Questions

Do Relaxers Cause Hair Loss?

They can damage hair, and that damage can look like thinning. The AAD's relaxer advice (a professional, new growth only, never hair that's already relaxed) is aimed at limiting that damage. Thinning at the crown has several possible causes, which the main causes of hair loss in women goes through.

Is Any Hair Relaxer Safe to Use?

No relaxer has been shown to be free of the cancer link, and none has been shown to cause it. The studies didn't record brands or ingredients. Using one less often, on a healthy scalp, is the lowest-exposure way to keep relaxing.

Is There a Lawsuit Over Hair Relaxers and Cancer?

Yes. In February 2023, a federal panel sent the federal cases to one court in Illinois for pretrial proceedings. The women suing claim relaxers caused or raised their risk of uterine, ovarian or breast cancer. Grouping the cases doesn't mean any court has found that relaxers cause cancer.