A new study has revealed a significant link between the use of chemical hair relaxers and an increased risk of developing multiple cancers, with some risks potentially rising by as much as 166 percent. Experts have long been concerned about the presence of formaldehyde, a known carcinogen, in many hair-straightening and relaxing treatments, including Keratin treatments and Brazilian blowouts.

To investigate the long-term health consequences, researchers from Emory University in Georgia analyzed data from the Sister Study, a comprehensive, long-term health initiative. This study involved over 50,000 U.S. women, aged 35 to 74, who had no personal history of breast cancer but had at least one sister diagnosed with the disease. Enrollment for the study took place between 2003 and 2009, with participants being followed through September 2021. For the final analysis, the researchers included data from 46,287 women, who were followed for an average of 13.1 years.

The study specifically focused on cancers with at least 100 reported cases during the follow-up period and assessed whether participants had used hair straighteners or relaxers in the 12 months preceding their enrollment. The findings indicated a significantly higher cancer risk among users of these products. Compared to non-users, women who used hair straighteners or relaxers faced a 166 percent higher risk of pancreatic cancer. Pancreatic cancer is particularly deadly due to the lack of a specific screening test, making early detection difficult.

Furthermore, the study found that women who used hair straighteners or relaxers also had a 71 percent higher risk of thyroid cancer and a 62 percent higher risk of non-Hodgkin's lymphoma. The risks escalated even further for frequent users, defined as those using the products more than four times per year. In this frequent-use group, the risk of pancreatic cancer more than doubled, while thyroid cancer and non-Hodgkin's lymphoma also showed elevated, though not statistically significant, risks. The researchers additionally observed a 'positive but imprecise' possible link between straightener use and kidney cancer.

Formaldehyde, commonly used as a preservative in hair products, can 'off-gas' as a gas over time, especially when exposed to heat. Repeated inhalation of these fumes can lead to minor side effects such as eye and respiratory irritation, and more serious health issues like an increased risk of head and neck cancers, particularly if the environment is poorly ventilated. The American Cancer Society has also noted that both animal and human studies have linked formaldehyde to various cancers, including those of the nose, upper throat, stomach, and an increased risk of leukemia.

Demographic data from the study highlighted significant variations in hair straightener and relaxer use across different racial groups. Approximately 66 percent of Black women, 25 percent of Hispanic/Latina women, and only 1.3 percent of non-Hispanic White women in the study reported using these products. Researchers emphasized that these novel findings expand the scope of adverse health outcomes associated with these products and underscore the need for further investigation to confirm results and identify specific cancer-contributing ingredients.

This study contributes to a growing body of evidence raising concerns about the long-term health effects of chemical hair treatments, especially within populations exhibiting higher usage rates. In response to these concerns, the European Union and at least ten U.S. states have either banned or proposed to ban formaldehyde and formaldehyde releasers in personal care products. In 2023, the Food and Drug Administration (FDA) proposed a national ban on these chemicals in hair straighteners, though it has not yet been enacted. Nevertheless, numerous states have proceeded with their own bans; for example, Washington's Toxic-Free Cosmetics Act will ban all intentionally added formaldehyde-releasing chemicals in cosmetics and personal care products starting January 1, 2027. The findings from Emory University were published in the Journal of the National Cancer Institute.