Does Hair Relaxer Cause Cancer?

What the 2022 Study Found

The research came out of the Sister Study, a project run by the National Institutes of Health that has followed tens of thousands of women for years. The analysis was published in October 2022, covering 33,497 women followed for nearly 11 years.

It found that women who used chemical straighteners more than four times in the previous year developed uterine cancer at a higher rate than women who never used them. Roughly double. That is the number behind every headline you have seen on this. The research itself is covered on The Hair Relaxer Cancer Studies, Explained.

What Double Actually Means Here

Uterine cancer is not common. Over a whole lifetime it affects a small percentage of women.

The researchers gave the actual numbers. An estimated 1.64% of women who never used straighteners would develop uterine cancer by age 70. Among frequent users, 4.05%.

Both things are true at once. That increase is real and worth taking seriously. It also takes the odds from roughly 2 in 100 to roughly 4 in 100, which leaves most women in both groups unaffected. Headlines report the doubling and leave out the starting point.

Linked To Is Not Caused By

A link means the illness showed up more often in one group than another. Causing it means the product produced it. Those are different claims and the gap between them is where these cases are fought.

The Sister Study watched what happened to women who did and did not use these products. It did not assign anyone to use them. So the women in the two groups differ in other ways too, and a study built that way can spot a pattern but cannot prove what caused it. In court, tying a product to one woman’s diagnosis is a separate fight decided on her own facts.

Which Cancers Are Involved

Uterine cancer is the one with the strongest evidence, especially endometrial cancer, which is the most common form. It is also what the federal litigation is built on. Some research has looked at ovarian and breast cancer too.

Fibroids are a different thing, non-cancerous and very common, and they sit differently in the litigation. That is covered on Hair Relaxers and Fibroids.

Why It Might Work That Way

Some of these products contain chemicals that interfere with hormones, including certain phthalates, parabens, formaldehyde or preservatives that release it, and bisphenol A.

The cancers being studied are hormone-driven, so that is the leading explanation for how a straightener could matter. Scalp burns and irritation from relaxers may also let more of the chemicals into the body. This is a working theory that researchers find plausible, not a proven mechanism.

How This Connects to the Lawsuits

The 2022 study is the foundation the cases are built on. The claim is that the companies should have warned women about a risk their own industry had reason to know about. For the legal picture, see Hair Relaxer Cancer Lawsuit and Hair Relaxer Lawsuit Updates.

What This Means for You

If you used relaxers and you are worried, the person to talk to is a doctor who knows your history. This page explains the research. It cannot tell you what caused anything.