Hair Relaxers and Dyes Linked to Increased Risk of Uterine Fibroids.
Hair Relaxers and Dyes Linked to Increased Risk of Uterine Fibroids
Recent studies led by SPH researchers found that Black women who used temporary chemical hair straighteners and hair dyes within the past 12 months had a higher risk of developing fibroids, which can cause heavy bleeding and other health problems when they grow.
Although hair relaxers have waned in popularity among Black women in recent years, millions of Black Americans still use these chemical hair straighteners, many of which contain harmful chemicals that may contribute to numerous adverse health outcomes, including uterine fibroids. A new study led by researchers at the School of Public Health have found that Black women who used relaxers within the last 12 months were at greater risk of being diagnosed with uterine fibroids—and have larger fibroid growth—than Black women who never used these hair treatments.
The study also found that recent use of temporary hair relaxers, as opposed to permanent hair relaxers, was more strongly associated with uterine fibroids incidence and growth. The findings were published in the American Journal of Epidemiology (AJE).
The findings build upon a growing body of research on the potential dangers of chemical hair straighteners and other hair products that are heavily marketed to Black women, who use these products to straighten curly or tightly coiled hair. In addition to uterine fibroids, past studies from SPH researchers with BU’s Black Women’s Health Study and other experts have linked hair relaxer use among Black women to an increased risk of uterine, ovarian, and breast cancers, as well as early onset of puberty. A 2025 SPH-led study, published in the journal Fertility and Sterility, also linked use of temporary hair dyes to increased risk of uterine fibroids among Black women.
Many of these hair products contain formaldehyde and/or endocrine-disrupting chemicals, such as phthalates, phenols, and parabens, which can disrupt hormones. Fibroids are noncancerous growths that form in or around the uterus and are typically not dangerous, but they can cause pelvic pain, bleeding, pregnancy complications, and other health issues with growth.
The AJE study is the first to examine the effects of using different types of relaxers. Temporary relaxers (such as keratin treatments) are more likely than permanent relaxers to contain formaldehyde and other chemicals that release formaldehyde when heated.
“Our findings add to growing evidence that hair products commonly used by Black women may contribute to uterine fibroid risk,” says study lead and corresponding author Lauren Wise, professor of epidemiology. “Given the widespread and often long-term use of these products, understanding their health effects is an important public health priority.”
The new findings follow multiple delays by the US Food and Drug Administration to formally propose a federal ban on formaldehyde and formaldehyde-releasing chemicals in hair-straightening products. The agency initially planned to propose this ban in 2023 and missed its latest deadline in December 2025.
For the AJE study, the research team utilized prospective data from the Study of Environment, Lifestyle, and Fibroids (SELF) to examine nearly 1,700 Black participants ages 23-35 between 2010-2012. Notably, the analysis also included repeated transvaginal ultrasounds among the participants, which provided prospective, image-based data on the presence of fibroids that was more reliable than self-reported information.
“This work aims to improve the investigation of environmental exposures in relation to fibroids, and the use of ultrasounds is directly relevant to clinical practice,” says study coauthor Sharonda Lovett (SPH’25), SPH alum and postdoctoral associate in the Department of Epidemiology. “It is unclear whether temporary hair relaxers also contain the same range of hormonally active ingredients known to have adverse health effects. , and fFuture studies should attempt to replicate our findings and conduct an exposure assessment of hair relaxer ingredients.”
The 2025 Fertility and Sterility study, which also utilized data from SELF participants, found that use of hair dyes within the last 12 months was linked to a 44-percent higher risk of fibroid incidence among Black women. The study was also the first of its kind to examine hair dye use and fibroid incidence.
“Similar to hair relaxers, we found that associations were strongest for non-permanent hair dyes, which may reflect differences in product formulations or frequency of use for temporary versus permanent hair products,” says study lead author Samantha Shildroth, a postdoctoral associate in the Department of Epidemiology at the time of the study and currently an assistant professor in the Shaw Institute of Public and Planetary Health at the University of New England. “Our studies collectively suggest that hair product use could be important drivers of uterine fibroid risk.”