Chemical Hair Straighteners

Chemical hair straighteners, also called relaxers, work by breaking up the natural chemical bonds that form and hold human curls. Chemical hair straighteners are widely popular because they’re effective at turning curly hair into straight hair. It’s a permanent hair straightening method that lasts until new hair grows out.

A protein called keratin makes up the structure of hair strands. Keratin has molecules known as sulfides. Sulfides can pair together to create a disulfide bond. As sulfide molecules reach toward each other to form disulfide bonds, the hair bends. The more the disulfide bonds in a strand of hair, the more it coils and curls.

Different brands of straighteners can affect hair differently. For example, some brands might dry hair out more, making it prone to breakage, according to professional hair stylist Tonya Herrell.

“I used to use this brand called Affirm, and I noticed that it made hair super dry. Clients might not notice, but I did because I know healthy hair. It just wasn’t giving it any life. I switched to a brand called Congo. It’s Black-owned and Black-created, and it keeps the hair lively and shiny,” Herrell told Drugwatch.

Chemicals in Hair Relaxers

Chemical hair straightening products use various chemicals to dissolve disulfide bonds, altering the protein structure’s shape in the hair and straightening it. Some of these chemicals, such as formaldehyde, can be toxic to humans.

Many chemical hair straighteners have proprietary formulas, so it’s not easy to see all the ingredients in each formula.

If used incorrectly or too often, these chemicals can cause long-term damage to hair and skin and increase the risks for other health issues, including cancer.

In the short term, chemical hair straighteners don’t cause many serious side effects. However, heavy, long-term use comes with the potential for unsafe toxicity and an increased risk of hormone-related cancers. According to some recent studies, Black women — who are more likely to use these products long term — are at the most risk.

Side effects of chemical hair straighteners affect not only people who receive hair treatments but also the salon staff who apply them. For instance, formaldehyde is a known carcinogen. It can lead to significant breathing and lung problems.

Unfortunately, even products labeled formaldehyde-free may contain chemicals that release formaldehyde when subjected to heat.

Parabens are chemicals routinely used in cosmetic hair care and skin care products. Shampoos, conditioners and other hair products often contain parabens because of their effectiveness against mold and harmful bacteria.

However, excessive paraben absorption can interfere with hormone production and cause endocrine dysfunction, affecting male and female reproduction. Girls going through puberty are particularly vulnerable to these effects.

Recent studies have linked chemical hair straighteners to cancers such as uterine cancer, ovarian cancer and breast cancer. Some links, such as the link to breast cancer, have had mixed results in studies.

Uterine cancer is the top cancer linked to hair relaxers. According to researchers, parabens, phthalates, formaldehyde and the toxic chemical Di(2-ethylhexyl) phthalate, or DEHP, are among the ingredients in relaxers that may cause cancer.

Researchers theorize that these chemicals affect hormones that could contribute to cancer development.

It’s important to note that the risk of uterine cancer may also increase with other factors that interfere with hormone balance. One of the biggest risks is excess body weight, according to oncologist Dr. Joseph Buscema of Arizona Oncology. There are two primary types of uterine cancer: endometrial cancer, which is more common, and uterine sarcoma, which is rare.

“The relationship between the increase in body weight, endometrial malignancy has been associated with the presence of excessive estrogen quantities in these individuals.  This factors into the development of endometrial cancer in younger cohorts of patients who have not gone through menopause, because of excess body weight, disturbance of ovulation that is associated with progesterone production to offset the proliferating influence of estrogen,” said Dr. Buscema.

Avoiding substantial weight gain and regular exercise are two ways women can reduce their uterine cancer risk, Dr. Buscema adds.

What Studies Say About Hair Relaxer Cancer Risk

A few recent studies have linked chemical straighteners to cancer. Some evidence presented is stronger than others, while other studies found a weaker link to breast cancer.

In addition to cancer, researchers have also linked hair relaxers to other women’s reproductive health issues such as uterine fibroids and endometriosis.

Chemical hair straightener companies have heavily marketed to Black women for years, and the use of these products is common in the community. In fact, according to a December 2023 study published in Environmental Research, up to 95% of self-identified Black women in the U.S. reported using chemical hair straighteners, or hair relaxers.

Researchers argue that heavy chemical straightener use among Black women has also increased their rates of uterine cancer. Kimberly Bertrand, associate professor of medicine at Boston University Chobanian & Avedisian School of Medicine, is one of the researchers who published the 2023 Environmental Research study.

“Compared to non-Hispanic white women, Black women have higher rates of aggressive subtypes of uterine cancer and are nearly twice as likely to die from their disease,” Bertrand said.

Many Black women who filed chemical hair straightener lawsuits after being diagnosed with cancer claim they were never warned of the risk by hair relaxer makers and that the companies targeted Black women. As of December 2024, 9,649 lawsuits were pending in Illinois federal court.

In Spring 2023, the FDA announced it would ban formaldehyde and formaldehyde-releasing chemicals in chemical hair straighteners because of the serious health risks these chemicals pose. The proposed ban was supposed to take effect in April 2024. The ban was delayed and was  expected to be implemented in July 2024. Most recently, the agency moved the target date to September 2024.

“Use of hair smoothing products containing FA [formaldehyde] and FA-releasing chemicals is linked to short-term adverse health effects, such as sensitization reactions and breathing problems, and long-term adverse health effects, including an increased risk of certain cancers,” the Agency said.

Some consumer advocates say that it has taken far too long for the Agency to act.

“We’re glad that the FDA finally decided to ban these products, which the Agency started planning to do in 2016. The research evidence has been clear for more than a decade,” Dr. Diana Zuckerman, president of the National Center for Health Research, told Drugwatch. ”But we have to wonder how many women have been harmed in the meantime, and why did it take the Agency so long to finally do the right thing to protect consumers?”