And they're taking cosmetic heavyweights to court in the U.S..
Sheila Bush is among them.
The 69-year-old has relaxed her hair every six weeks for most of her life.
"Growing up in the 60s, I went to a segregated school where they had Blacks on one side and the whites on the other. And so, we would hear negative things about our hair because that was just the time, you know, race was a problem back then."
Bush was diagnosed with uterine cancer in her late 50s.
Last winter, she started seeing ads pop up on TV and her social media feeds looking for women to file lawsuits against more than a dozen cosmetic companies ... including L'Oreal and Revlon.
The recruitment campaign launched shortly after a study had come out from the U.S. National Institutes of Health.
It found an association -- though not a causal link -- between the frequent use of chemical hair relaxers and uterine cancer.
The study looked at more than 33,000 women.
Those who used the products more than four times in the previous year were more than twice as likely to develop uterine cancer compared to those who didn't use them.
The main thrust of the lawsuits?
Those companies sold harmful products and should have warned customers about the risks -- but didn't.
L'Oreal and Revlon told Reuters their products are subject to rigorous safety reviews.
"We do not believe the science supports a link between chemical hair straighteners or relaxers and cancer," Revlon said.
The companies noted that the NIH study didn't draw definitive conclusions and said more research is warranted.
BUSH: "Well, once I heard about the lawsuit and there was a possibility that chemicals, relaxers could be related to different types of cancer, if that's the case, if we find out that that's the case, I would like to see that relaxers were taken completely off the market."
There are more than 7,000 similar lawsuits so far from all over the country.
Plaintiffs' lawyers involved in the case say hair straighteners such as L'Oreal's Dark & Lovely and Revlon's Creme of Nature are marketed overwhelmingly to Black women.
BEN CRUMP: "Obviously, it is not lost on anyone that many of the women who use these chemical relaxers are women of color, African American women, Black women throughout America and the world."
Ben Crump filed the first hair relaxer lawsuit on behalf of a Missouri woman shortly after the NIH study was published. Crump is known for representing the family of George Floyd, the Black man murdered by a Minneapolis police officer in 2020.
He says the potential risks should be seen as a civil rights issue.
"They were told, 'If you want your hair to be straight, if you want to look professional, if you want to fit in, you use a relaxer.'"
Some product liability experts interviewed by Reuters say the women - who are suing multiple companies - could face a hurdle when it comes to receipts.
Without them, plaintiffs could struggle to prove they used specific products.
As for the companies involved... they want the cases dismissed.
In court filings, they've argued - if this is the first study to link the products to uterine cancer - how could they have known about the risks?
L'Oreal added it is committed to offering the best hair products for all identities and cultures.
Namaste, which markets ORS Olive Oil relaxers, said all ingredients in its products are approved for cosmetic use by U.S. regulators.
"We do not believe the plaintiffs have shown, or will be able to show, that the use of Namaste hair relaxer products caused the injuries that they allege in their complaints," a lawyer for Namaste and its parent company, Dabur India, said in an email response to Reuters.
The other companies declined to comment or didn't respond to requests.
