New research has found “forever chemicals” in the lining of period underwear, the wrappers of tampons and in other menstruation products.

Forever chemicals, or PFAS, are man-made compounds that can potentially accumulate in the body over time and take years to break down in nature. PFAS, which stands for per- and polyfluoroalkyl substances, have been implicated in a number of serious health effects, including some cancers, high blood pressure, disruption of the endocrine system and developmental problems in children.

Researchers from the University of Notre Dame studied more than 120 different menstruation products – menstrual cups, pads, underwear and tampons – sold in the United States.

The research found forever chemicals in some, but not all, of the products. Although the researchers did not provide specific details, the study found that “a good fraction” of the period underwear products had detectable levels of PFAS in the lining, said Graham Peaslee, a physics professor at the University of Notre Dame who led the research.

“It shows that it’s not everywhere,” Peaslee said. “But it’s certainly a concern, especially in two or three product lines.”

None of the tampons tested had forever chemicals, but forever chemicals were found in some tampon plastic wrappers and applicators, liners and incontinence pads.

“There’s no safeguards on this,” Peaslee said. “Nobody would have known because nobody checks this sort of stuff.”

The study does not include the names of the different brands tested. Peaslee said that it’s because the research is still ongoing and that their work isn’t exhaustive.

“We don’t want to pick on a brand at this point because we just don’t know enough,” Peaslee said.

The full details of the study, including the number of products implicated and the amount of PFAS detected, are expected to be presented Sunday at the American Chemical Society meeting in San Francisco.

This year, the period underwear company Thinx announced that it reached a $5 million settlement in a class-action lawsuit regarding the marketing of its products. The lawsuit accused Thinx of misleading customers by claiming that its underwear was free of harmful chemicals.

The claim was based on earlier research conducted by Peaslee’s lab, which tested the underwear following a 2019 request by Sierra, the magazine of the Sierra Club.

Thinx denied the allegations in the lawsuit and denied any wrongdoing. The company did not respond to a request for comment by the time this article published.

“The good news is that there are products out there without PFAS,” Peaslee said. “In fact, the majority of products tested did not have intentional PFAS added. But we need better labeling for the consumer to be sure.”

There are more than 12,000 different types of PFAS with a range of grease-, stain-, water- or fire-resistant properties. These forever chemicals can be found in a number of household products, like some types of dental floss, certain nonstick cookware and even bags of microwave popcorn.

PFAS have also been detected in clothing, like school uniforms and rain jackets. What’s not clear is whether someone’s skin can absorb these forever chemicals through the clothes they’re wearing, Peaslee said.

But experts do know these forever chemicals are water soluble, which means products with PFAS that eventually end up in landfills, groundwater, and ultimately our water and food supplies, as well.

Nearly half of the nation’s tap water is tainted by PFAS, according to a recent study by the U.S. Geological Survey. And most Americans have detectable amounts of PFAS in their blood.

In March, the Environmental Protection Agency proposed the nation’s first regulations to limit forever chemicals in drinking water. At the time, agency officials said they expect to finalize the rule by the end of the year.