4 women sued hair straightener manufacturers over claims the products caused uterine cancer. Here's why you shouldn't be worried just yet.

• As other cancer deaths decrease, the mortality rate for uterine or endometrial cancer is on the rise.

• Black women make up 5 to 10% of endometrial cancer patients, but 40 to 50% of endometrial cancer deaths.

Uterine cancer is on the rise, and women across the country are pointing the finger at chemicals in hair products.

Recent national data suggests hair straighteners that use harsh chemicals like formaldehyde — used both in salons and at home — might have a link to endometrial cancer, or cancer in the lining of the uterus, the most common gynecologic cancer in the US. The National Institutes of Health found women who said they frequently used chemical hair straighteners had a 4% likelihood of developing this cancer — nearly double the 1.64% likelihood for women who did not use those products.

Following the NIH report, four women filed federal lawsuits against L'Oréal and other chemical hair straightener sellers, claiming their products had a role in their uterine cancer diagnosis. Women have even told CNN they are cutting back on chemical hair products in fear cosmetics can cause uterine cancer.

Black women, a group historically left out of cancer research, are uniquely impacted by uterine cancer. They are twice as likely to be diagnosed with an aggressive form of endometrial cancer, which is a type of uterine cancer; they make up 5 to 10% of endometrial cancer patients, but 40 to 50% of endometrial cancer deaths.

Sixty percent of those who reported using hair products in the NIH study were Black women, who spend more on beauty and hair products compared to other demographics, per Nielsen.

Though chemicals in cosmetics appear as a likely culprit for uterine cancer's rise, top experts say not to jump to conclusions.

Doctors and scientists from Yale, Johns Hopkins, and the National Cancer Institute who specialize in uterine cancer told Insider that while the association between the disease and hair chemical use is "hypothesis generating," researchers still need to conduct detailed trials with larger, more diverse sample sizes.

So far, no definitive data suggests a chemical in cosmetics could cause endometrial cancer, Dr. Amanda Nickles Fader, the vice chair of gynecologic surgical operations at Johns Hopkins, told Insider.

"It's certainly hypothesis generating and thought provoking and may lead to hopefully further data," said Dr. Mitchell Clark, an assistant professor of obstetrics, gynecology & reproductive sciences at the Yale School of Medicine. "But I don't know that there's enough data there to completely point the finger that this is the smoking gun for why we see this difference in outcomes."

Endometrial cancer will soon be the third most common cancer among women — and scientists don't know what's behind the growth

While cancer deaths in general have decreased for Americans, the death rate for uterine cancer has been increasing since 2015.

Fader said endometrial cancer had previously been thought of as a "rare," treatable cancer, but alarming increases in deaths and diagnoses suggest the disease will overtake colon cancer as the third most common cancer in women, behind breast and lung cancers.

"I study endometrial cancer, and it's actually one of the most important cancer-related public health problems in women right now," Fader said.

Clark said the most common type of endometrial cancer can present as bleeding in women who are pre- or post-menopausal and has known risk factors like obesity and diabetes.

But doctors tend to catch a rarer form of endometrial cancer after it's already progressed to an advanced stage, making the cancer more difficult to treat, Clark said. He said this rarer form doesn't always present like typical endometrial cancer, and the risk factors for it aren't fully known.

Uterine cancer is under-studied, and Black women are historically excluded from trials

Part of the issue with endometrial cancer's rise is researcher still aren't sure what causes the disease — and research to study the cause is scant and underfunded.

Women's health problems in general are underfunded and understudied, and Fader said clinical research on uterine cancer and federal funding for these studies has lagged behind that for other cancers.

Megan Clarke, an investigator with the National Cancer Institute who helped identify the rise in uterine cancer, told Insider in an interview that researchers do not yet know what factors are causing the increase of this cancer among women — but they know the disease disproportionately harms Black women.

Clarke said Black women have a higher mortality rate for uterine cancer irrespective of how advanced the disease was when doctors first spotted it.

It's too soon to say hair products are causing the uterine cancer death discrepancy between Black and white women

Clarke said the NIH analysis was "important" in demonstrating an association between hair straightener use and uterine cancer, but more research is needed before calling it a risk factor.

For instance, the NIH report linking hair chemicals to uterine cancer had major limitations. Researchers didn't ask about specific products or chemicals that the women used, making it hard to identify what brands or ingredients might be behind the trend. The study was also observational, meaning scientists didn't control for other factors that might have contributed to a cancer diagnosis.

And only 378 women — 1% of total the sample — developed uterine cancer in the study.

Right now, Clark said public awareness of uterine cancer's rise is imperative to helping bring down deaths. People with uterus should regularly visit their gynecologist, and remain aware of endometrial cancer symptoms: bleeding, pelvic pain, and changes in bladder or bowel function.

Given medical gaslighting within the healthcare system, Clark also said people who don't feel their doctor is taking their concerns seriously should seek a second opinion immediately. "Early detection and early stage are the key to improve survival," he said.