Chemical Hair Straightener Side Effects

The most common side effects of chemical hair straighteners and relaxers are hair damage and skin irritation. However, the ingredients in many hair relaxers are also associated with some severe hazards to your health.

Widely used and potentially harmful compounds found in many chemical hair straightening products include benzophenone-3, cyclosiloxanes, diethanolamine, formaldehyde, parabens, phthalates, sodium hydroxide and triclosan.

“Chemical hair relaxers often contain strong alkaline agents like sodium hydroxide, guanidine hydroxide or ammonium thioglycolate,” Dr. Janet Vafaie, MD, FAAD, a Board-Certified Dermatologist, told Consumer Notice. “Over time, they may weaken the hair shaft, leading to breakage and permanent hair loss due to scarring alopecia.”

The World Health Organization’s International Agency for Research on Cancer classifies formaldehyde, a key ingredient in many hair relaxers, as a carcinogen. 

Some governments, like Brazil and Canada, have prohibited or limited the use of formaldehyde in chemical hair straighteners. The Nigerian government issued a warning against using hair products containing formaldehyde. 

The U.S. Food and Drug Administration (FDA) has repeatedly missed deadlines to rule on banning formaldehyde-containing hair relaxers. However, in October 2024, they released a fact sheet warning consumers and salon professionals to be careful with these products. 

According to the agency, you should check labels for ingredients like formalin or methylene glycol and look out for skin irritation and breathing problems. If the ingredients aren’t clear, consult your stylist or choose a different product. If you experience adverse reactions, report them to your doctor and the FDA.

The Occupational Safety and Health Administration requires salons to have proper ventilation since heating these products can release formaldehyde gas. Salons should follow safety regulations to limit formaldehyde exposure in the air.

A 2022 National Institutes of Health study found that women who used chemical hair straightening products at least four times in the previous year were more than twice as likely to develop uterine cancer than those who did not.

Dr. Alexandra White, head of the National Institutes of Health’s Environment and Cancer Epidemiology group and lead author on the new study, noted, “This doubling rate is concerning. However, it is important to put this information into context – uterine cancer is a relatively rare type of cancer.”

National Institutes of Health researchers previously reported on the link between hair straightening products and cancer, finding increased risk for both breast and ovarian cancers. Women who used hair straighteners at least every five to eight weeks were about 30% more likely to develop breast cancer.

The authors state that study results must be replicated before medical professionals can make more firm recommendations about chemical hair straighteners and cancer. 

Some consumers who developed severe side effects, including uterine cancer, have begun filing chemical hair straightener lawsuits against beauty industry brands selling these products.

As of March 2025, there were 9,788 pending lawsuits in a hair straightener multidistrict litigation (MDL) in an Illinois federal court.

The best way to avoid the side effects of chemical hair relaxers is to use alternative methods to straighten your hair. While nonchemical hair straightening methods vary in effectiveness, experimenting with them is typically safe. For example, flat irons are safe but may damage hair if overused.

Using a natural product like coconut oil can help to relax the cuticle and eliminate frizz.

If you are a consumer or a hair stylist who uses hair straightening treatments, you could risk exposure to formaldehyde, a known asthmagen and carcinogen. Parabens, another chemical found in hair straighteners, are linked to reproductive problems.

Manufacturer claims of formaldehyde-free products can be misleading. Formaldehyde-free hair straighteners do not technically contain formaldehyde as an ingredient. However, they can include other chemicals that release formaldehyde when exposed to the high heat necessary for straightening treatments to work.

Though more studies are required, federal and state governments are concerned about the potential for adverse impacts from many chemicals in hair straightening products since research has proven a link to cancer and other serious health problems.