For decades, chemical hair straighteners have been a staple in the beauty routines of millions of women, particularly Black women for whom these products promised manageability and conformity to Eurocentric beauty standards. What these women weren't told—what manufacturers allegedly knew and concealed—was that the chemicals they were applying to their scalps every few weeks might be causing cancer.

In October 2022, a landmark study from the National Institutes of Health changed everything. Researchers analyzing data from nearly 34,000 women found that those who frequently used chemical hair straighteners had more than double the risk of developing uterine cancer compared to women who never used these products.

The NIH Sister Study

The findings came from the Sister Study, a long-term research project tracking the health of women whose sisters had been diagnosed with breast cancer. While the study's original focus was breast cancer, researchers also tracked other health outcomes—including uterine cancer, which is rising in the United States at alarming rates.

When scientists analyzed the data, the connection to hair straighteners emerged with disturbing clarity. Women who reported using chemical straightening products more than four times per year were approximately 2.5 times more likely to develop uterine cancer than women who reported no use. The more frequently women used these products, the higher their risk climbed.

For context, uterine cancer is relatively rare—roughly 3% of women will develop it in their lifetime. But for frequent straightener users, that baseline risk more than doubled. And because Black women use these products at significantly higher rates than other groups, the racial implications are stark.

The Chemicals Involved

Chemical hair straighteners work by breaking down the protein bonds in hair, allowing it to be reshaped into a straighter configuration. This process requires powerful chemicals, and many of the compounds found in these products are known or suspected endocrine disruptors—substances that interfere with the body's hormonal systems.

Formaldehyde and formaldehyde-releasing compounds are common ingredients. Formaldehyde is a known human carcinogen, classified as such by the International Agency for Research on Cancer. When heated during the straightening process, these compounds release formaldehyde gas that users inhale and that contacts their scalps directly.

Other concerning chemicals include phthalates, parabens, and various fragrance compounds—all of which have been linked to hormonal disruption. The scalp is highly vascular and permeable, meaning chemicals applied there can be absorbed directly into the bloodstream. Women who use straighteners regularly are exposed repeatedly over years or decades.

Why Uterine Cancer Specifically

Uterine cancer is heavily influenced by hormonal factors. Estrogen exposure drives the growth of uterine tissue, and conditions that increase lifetime estrogen exposure—early menstruation, late menopause, obesity, never having children—are all known risk factors for uterine cancer.

Endocrine-disrupting chemicals can mimic or amplify estrogen's effects in the body. When these compounds are absorbed through regular scalp application of hair straighteners, they may create the same kind of prolonged estrogen stimulation that other known risk factors cause. Over years of use, this hormonal disruption may promote the development of uterine cancer.

The mechanism makes biological sense, the epidemiological data supports the connection, and the companies that manufactured these products had access to information about their ingredients' hormonal effects. What they chose to do with that information—or not do—is at the heart of the litigation.

A Disparate Impact

The hair relaxer crisis isn't just a public health issue—it's a racial justice issue. Black women are far more likely to use chemical hair straightening products than women of other races, often beginning in childhood and continuing for decades. This usage pattern reflects both cultural pressures and a beauty industry that has long marketed these products specifically to Black communities.

Studies estimate that roughly 90% of frequent straightener users in the NIH Sister Study were Black women. If the products do cause cancer—and the evidence increasingly suggests they do—Black women bear the overwhelming burden of that harm. They were targeted as consumers and are now suffering the consequences as patients.

What Manufacturers Knew

The litigation alleges that manufacturers knew their products contained harmful chemicals and either failed to warn consumers or actively concealed the risks. Internal documents may reveal what companies understood about the carcinogenic and endocrine-disrupting properties of their ingredients. If these companies had information suggesting their products could cause cancer and chose to keep selling them without warnings, that's the foundation of a failure-to-warn claim.

For women who used these products for years, trusting the manufacturers to tell them about any serious risks, the sense of betrayal is profound. They made choices about their beauty routines without information that might have changed those choices entirely.

What This Means Going Forward

The NIH study isn't the final word—more research continues—but it's strong enough that the FDA has proposed banning formaldehyde from hair straightening products entirely. That regulatory response validates what the research suggests: these products pose genuine health risks that consumers were never adequately warned about.

For women who developed uterine cancer after years of using chemical hair straighteners, the litigation offers a path to compensation and accountability. Understanding the scientific connection between these products and cancer is the first step in evaluating whether you may have a claim.