Chemical Hair Straighteners & Cancer Risks

Researchers have linked endocrine-disrupting chemicals, including parabens, metals, bisphenol A and formaldehyde contained in many hair straightening products, to the risk of developing cancer.

For example, a 2022 study from the National Institutes of Health found that the risk of uterine cancer doubles in women who use chemical hair straighteners more than four times per year.

Chemicals Found in Hair Straighteners and Associated with Cancer

• Bisphenol A
• Formaldehyde (methylene glycol and formalin)
• Metals
• Parabens

Researchers in the 2022 study didn’t investigate specific brands or ingredients in hair products, but they acknowledged that several chemicals commonly found in chemical hair straighteners create a higher risk of uterine cancer.

Keep in mind that not every person who uses hair relaxers will develop cancer. For example, professional hair stylist Tonya Herrell told Drugwatch that she has clients and family that have been using hair relaxers for years, and they have not developed cancer. 

“In all my years dealing with relaxers, I have never encountered a case where the relaxer is a direct cause of their cancer. My relatives and aunties have been getting them for years,” Herrell said. 

Scientists theorize that chemicals in hair relaxers can affect hormones in the body and lead to hormone-related cancers, such as uterine, ovarian and breast cancer. A further NIH study also examined potential links between hair products and other cancers, particularly those that develop in response to hormones, including ovarian cancer, breast cancer and uterine cancer.

Medical professionals raised concerns about the possibility of ingredients in hair relaxers getting absorbed through the scalp and having estrogen-like properties in the body.

“Research is still developing as to exactly how hair straightening products and the toxic substances within them cause cancer. But hair relaxers or straighteners may cause lesions or burns on the scalp. It is currently believed that these injuries may make it easier for the endocrine-disrupting chemicals (EDCs) and other toxic chemicals to enter the body,” said Moshe Horn, an attorney with Simmons Hanly Conroy who has been litigating these cases and is familiar with the science of hair relaxer cases.

Formaldehyde

Heat usually activates chemical straightening solutions. When a stylist heats the solution, formaldehyde in the products gets released into the air as a gas. The International Agency for Research on Cancer (IARC) identifies formaldehyde as a human carcinogen based on leukemia and nasopharyngeal studies. The IARC studies have found significant evidence that formaldehyde causes nasopharyngeal cancer, strong but not sufficient evidence of leukemia, and limited evidence of sinonasal cancer.

Parabens

This group of chemicals, often used as preservatives in cosmetic products, foods and pharmaceuticals, has a high endocrine-disruption capacity. They disturb the hormones and reproductive systems of men and women and may increase the risk of certain cancers. Parabens are ubiquitous in our environment and several studies have linked exposure to this group with breast cancer, as well as various reproductive health issues in males.

Bisphenol A (BPA)

This chemical can interact with estrogen receptors, a likely reason why receptors can trigger the development of multiple cancers. Bisphenol A can also act as an androgen (largely responsible for male sexual development) antagonist and can cross the placenta from mother to fetus, although the placenta reduces concentration en route. BPA is metabolized in the liver and excreted in the urine with a plasma half-life of approximately six hours.

Permanent chemical hair straighteners and other hair products are most strongly associated with hormone-sensitive cancers, including health risks like uterine, breast and ovarian cancers. So far, studies show uterine cancer is the most strongly linked to hair relaxers.

Researchers discovered that some chemicals in chemical straighteners, including parabens and phthalates, get absorbed through the skin and disrupt the endocrine system. Another common ingredient, formaldehyde, is a known human carcinogen. Studies show that the toxic chemical damages human DNA in early forms of white blood cells in bone marrow, and scientists have linked it to myeloid leukemia.

Findings from the 2022 NIH study provided the first epidemiological evidence of the link between the use of chemical hair straightening treatments and uterine cancer. Women who applied chemical straighteners more than four times a year had more than double the risk of uterine cancer.

Uterine Cancer

After the 2022 NIH study finding on uterine cancer, a December 2023 published in Environmental Research found postmenopausal Black women who said they used hair relaxers more than twice a year for more than five years had at least a 50% increase in their risk of developing uterine cancer.

Ovarian Cancer

In one 2021 study published in Carcinogenesis, researchers followed up with more than 200 women subsequently diagnosed with ovarian cancer from the Sister Study. Over a period of 10 years, they found that frequent use — more than four times in a year — was associated with an increased risk of ovarian cancer, particularly non-serous ovarian cancer (but was actually inversely associated with serous ovarian cancer).

Breast Cancer

An NIH study published in the International Journal of Cancer showed that women who used chemical straighteners had a higher risk of developing breast cancer than those who didn’t — and a 30% increased breast cancer risk if they used them every five to eight weeks.

Michele Lynn developed breast cancer after decades of using hair relaxers, her husband Mike told Drugwatch. Mike didn’t realize there was a link between Michele’s cancer and chemical hair straighteners until after she passed at age 43.

“She was always very healthy and very fit,” Mike said, baffled by Michele’s cancer diagnosis. “She never smoked, wasn’t a heavy drinker and wasn’t overweight. When she was diagnosed, the BRCA test showed she wasn’t a gene carrier, so it wouldn’t affect our daughter.”

Researchers from the 2022 study that connected chemical hair straightening treatments to cancer didn’t collect information on specific brands and ingredients in chemical hair straighteners. However, they listed parabens, phthalates, bisphenol A, formaldehyde and metals, which are common in chemical hair straighteners, as chemicals that can cause cancer.

While there is no definitive collection of brands that are linked to cancer, people who developed cancer filed chemical hair straightener lawsuits and claimed the brands they used caused them to develop cancer.

It’s important to note that researchers are still studying the link between chemical hair straighteners and cancer. More studies and data are needed.

Currently, lawyers are accepting cases from people who developed uterine, endometrial, breast and ovarian cancer because the science for these cancers is the strongest.

Studies have shown that Black women have a greater risk of developing cancer from hair relaxer use because they are typically heavy users. Sixty percent of the participants in the 2022 NIH study who reported using chemical hair straighteners were Black women, leading researchers to conclude that the exposure burden was higher among that demographic.

According to Kimberly Bertrand, associate professor of medicine at Boston University Chobanian & Avedisian School of Medicine and one of the authors in the 2023 study in Environmental Research, up to 95% of self-identified Black women had used hair relaxers.

Some Black women also claim that manufacturers marketed hair straighteners to Black women, whose naturally curly hair made them potential buyers, and many of these consumers have filed chemical hair straightener lawsuits.

“It appears that Black women are in greater danger than women of other demographics,” said Horn.