Formaldehyde is a colorless, flammable, and strong-smelling chemical, most widely known for its use as embalming fluid. The National Toxicology Program officially listed the substance as a known human carcinogen, or substance that causes cancer, in 2011. According to the American Cancer Society, exposure to formaldehyde has been linked to cancer in both lab studies in animals and people.
But in that time, formaldehyde has remained a common ingredient in relaxers.
This is the first time the FDA has moved to ban the chemical in hair straighteners—but it has been on regulators’ radar for some time. The agency started advising users of relaxers about possible exposure to formaldehyde in 2010. The FDA warns that formaldehyde in the straightener can be released into the air as a gas—which can cause health problems if inhaled or touched. Recent studies have also identified chemical straighteners as having possible long-term effects—particularly in cases of uterine cancer.
In 2022, the National Institutes of Health found that women who used chemical straighteners had a higher rate of uterine cancer than those who did not. Researchers found that 1.64% of women who had never used hair straighteners would develop uterine cancer by the age of 70. For women who frequently used relaxers, that number increased to 4.05%.
“It’s over double, right? You may say, ‘oh my gosh’, the risk increases by more than 100%. But again, you have to take into account that the risk of uterine cancer is so low in general, and they had fewer than 400 cases in that study,” says Werner. “So, looking at the absolute number, it’s not that big of an increase, but we’re always looking for things that potentially increase risk.”
