The U.S. Food and Drug Administration (FDA) has proposed a ban on the use of formaldehyde in hair relaxers as it is linked to short and long-term adverse health effects, including the risk of cancer.

Hair smoothening and straightening products that contain formaldehyde release the toxic chemical when heated.

"Breathing in formaldehyde gas can be harmful and cause immediate reactions ranging from irritation of the eyes and throat to coughing, wheezing, or chest pain to chronic or long-term problems such as more frequent headaches, asthma, skin irritation, and allergic reactions and possibly cancer," FDA said in a fact sheet.

The agency discourages consumers from buying and using hair-smoothing products containing formaldehyde or related ingredients for home use. It recommends people check the label before purchasing and avoid buying products without a list of ingredients.

The ban could potentially come into effect by April 2024.

Formaldehyde is a highly toxic gas used in the production of various household products, cosmetics, medicines, fertilizer, paper, plywood and some resins. It is also used as a food preservative. According to the Centers for Disease Control and Prevention(CDC), exposure to formaldehyde can irritate the skin, throat, lungs and eyes and repeated exposure can possibly lead to cancer.

What do studies say?

The International Agency for Research on Cancer (IARC) classifies formaldehyde as a human carcinogen. Formaldehyde exposure from chemical hair straighteners is known to increase the risk of uterine, ovarian and breast cancer.

A study published in the National Institute of Environmental Health Sciences last year suggests that women who frequently use hair straightening products (more than four times a year) face over twice the risk of uterine cancer compared to those who do not use such products. Although the study has not examined specific brands or ingredients that elevate the risk, researchers attribute it to the parabens, bisphenol A, metals and formaldehyde in hair straightening products.

A team that evaluated the association between ovarian cancer and hair straighteners in a 2021 study found an increased risk with frequent use of the products.

In another research conducted in 2019 to evaluate breast cancer risk by ethnicity, a higher risk was associated with hair straightener use and permanent dye, especially among Black women.

The chemicals used in hair relaxers can disrupt the endocrine system and can cause reduced fertility in women, according to a study published in the American Journal of Epidemiology.