Hair Relaxers and Uterine Cancer: What the NIH Study Found

Chemical relaxers and straighteners have been part of many women’s routines for decades. In 2022, a National Institutes of Health¹ study linking them to uterine cancer made headlines. If you’ve used these products for years, here is what the research does and doesn’t show.

What the study found

The Sister Study followed more than 33,000 U.S. women aged 35 to 74 for almost 11 years. During that time, 378 developed uterine cancer.¹

• Women who used straightening products more than four times in the prior year were more than twice as likely to develop uterine cancer as women who didn’t use them.¹
• Researchers estimated that by age 70, about 1.64% of never-users would develop uterine cancer, compared with about 4.05% of frequent users.¹
• Hair dyes, bleach, highlights and perms were not linked to uterine cancer in this study.¹

The lead researcher called the doubling concerning, but noted that uterine cancer is relatively rare.¹

What it can’t tell us

• It shows an association, not proof of cause. It was the first study to look at this question, and the authors called for others to replicate it.²
• Use was self-reported for the prior 12 months.²
• No brands or ingredients were recorded. The researchers noted that chemicals found in some straighteners, such as parabens, bisphenol A, metals and formaldehyde, could play a role. Scalp burns and sores may increase absorption.¹

A 2026 analysis of the same study group found possible links between straightener and relaxer use and thyroid and pancreatic cancer, with little sign that more frequent use meant higher risk. The authors said more research is needed.³

Who may be most affected

About 60% of the women who reported using straighteners were Black. The study didn’t find a different link by race, but because Black women often use these products more and start younger, researchers said the findings may matter more for them.¹

Practical steps

1. Consider spacing out treatments or trying styles that don’t need chemical straightening.
2. Avoid scalp burns. Ask your stylist about a base or protective layer, and say something right away if it burns. Our guide to traction alopecia covers other styling damage.
3. Know the signs: any bleeding after menopause, or bleeding between periods in perimenopause, needs a medical visit.
4. Tell your clinician about long-term use when discussing your health history.

Our article on keratin smoothing treatments and formaldehyde covers salon smoothing services.

Try: “I’ve used chemical relaxers for 30 years and I’ve read about the uterine cancer study. Does that change anything about the symptoms I should watch for or the checkups I need?”

Hair, Everywhere includes a Hair Check, a monthly Hair Log, a gentle-styling checklist and a visit script. Use them to track treatments, scalp reactions and changes in your hair. See the book.