Here's Why It's So Hard to Know If Your Period Underwear Is PFAS-Free

Thinx period underwear

Verywell / Thinx

Key Takeaways

  • A class action lawsuit against Thinx is highlighting how period underwear brands can't always prove their products are free of harmful toxins, despite marketing claims.
  • The chemicals of concern, called PFAS, are human-made compounds that persist in the environment and human body. Many brands don't know their products contain PFAS.
  • Very few products are labeled "PFAS-free," but experts believe it will become easier to identify such products as brands learn about its presence.

Period underwear brand Thinx settled a class action lawsuit last week regarding the presence of per-and polyfluoroalkyl substances (PFAS) in their products.

While Thinx advertised its products were free of harmful chemicals, Sierra reporter Jessian Choy was able to prove otherwise back in 2020 with the help of Graham Peaslee, PhD, a physics professor at the University of Notre Dame.

PFAS, often referred to as “forever chemicals,” can take years to break down and contain numerous harmful toxins that can cause health problems, including cancer.

News of the lawsuit is calling into question the safety of the materials in the undergarment. It’s also highlighting just how hard it is to know whether or not period underwear has PFAS.

"In most industries, when [a manufacturer] discovers they have been using a 'forever' chemical with known toxicity in their products, they tend to take a precautionary approach and back away from using it," Peaslee, who spoke with Thinx in 2020 about his study results, told Verywell via email. "But Thinx didn't think it was that big of an issue. The settlement seems a bit like karma."

Why PFAS in Period Underwear Is Harmful

PFAS can enter the body through multiple routes, including your nose, mouth, and skin. Overexposure can lead to health outcomes including hormone disruption, high blood pressure, cancer, and birth defects (if exposed during pregnancy).

Consumers are often tasked with avoiding PFAS on their own. According to the Green Science Policy Institute, clothing containing PFAS is usually waterproof but breathable, like rain gear, ski gear, athletic gear—and now, leakproof underwear.

People who wear Thinx period underwear could be exposed to PFAS through direct skin contact.

“The concerning aspect is that these products come into contact with very sensitive parts of our bodies,” Marta Venier, PhD, assistant professor in the School of Public and Environmental Affairs at the University of Indiana in Bloomington, told Verywell. “The risk for dermal absorption is potentially higher, because it’s an area that is more susceptible for absorption.”

Still, researchers do not know what levels of PFAS are most dangerous, or how much exposure time is necessary to pose a health risk.

As a result, it’s difficult to limit PFAS exposure (though the Environmental Protection Agency is trying). The “easiest” thing to do is to advise avoiding the chemicals altogether.

That’s no easy ask. Most companies don’t test products for PFAS before marketing to consumers, so there’s not always a guarantee that garments or other items are safe.

"This is the gist of that last four or five PFAS research papers I've published: Sometimes PFAS is added intentionally and sometimes it is unintentional, but in every case, there is nothing in the label that indicates its presence in the product," Peaslee said. "As soon as the studies come to light, there is market demand away from using PFAS."

Regulations Are Needed, But Litigation Is More Realistic

Clothing manufacturers are not required to prove that their products are PFAS-free before putting them on sale. California, however, has a newly enacted law to prohibit the use of PFAS in cosmetic products, but this won’t go into effect until 2025. Without regulation, it is unclear just how many common clothing items may contain PFAS.

“A lot of PFAS usage is unintentional—brands don’t necessarily even know that it’s gotten into their products,” Lydia Jahl, PhD, a science and policy associate with Green Science Policy Institute, told Verywell.

Thanks to period underwear litigation, Peaslee thinks we'll see real change sooner rather than later.

"It is odd that the U.S. uses litigation to drive change, while Europe uses laws, but the litigation [route] does get products changed more quickly—years as opposed to decades," he said.

What Thinx Users Think

Grace Mooshian, a grad student studying nutrition, started using Thinx about a year ago. For Mooshian, the underwear has been a useful investment for her on-the-go life; she doesn’t have to take breaks in her clinical rotations to change a tampon, she’s saved money on period products, and she feels that she has created less waste because of it.

Because of these positives, Mooshian isn’t sure if she will stop using Thinx despite the lawsuit. And she’s not sure she wants to return to the inconveniences and environmental impact of pads and tampons, either.

“PFAS is terrifying,” Mooshian said. “Is it upsetting to find PFAS in a menstrual product and something I wear my body? Yes. Do I also know it’s in literally everything else in my life? Yes.”

Pads and tampons can also contain harmful chemicals, which Mooshian said she's been trying to avoid.

“For me, it’s kind of like ‘what’s the lesser evil?’” she said.

Is Any Period Underwear PFAS-Free?

It’s near impossible to ensure a piece of clothing is PFAS-free. But independent investigations, like the article that prompted the Thinx lawsuit, are helping. For instance, last year, public interest advocacy group CoPIRG uncovered PFAS usage—including any plans to phase out that usage—across 30 major retailers.

Peaslee said he's tested a few period underwear samples in his lab—too few to aggregate the meaningful sample size necessary to publish a study, but enough to say that the brand Luna appears free of PFAS.

Peaslee suspects that following the successful movement to remove PFAS across other industries, like food packaging and cosmetics, period underwear brands will actively work to remove the chemicals from their manufacturing processes and label products accordingly.

"The good news is that if something is labeled PFAS-free, it probably is, because somebody has asked their supply chain to not use PFAS," he said. "Of course, spot-checking will help confirm this, but this [labeling] is likely to be the path forward for most industries discovering PFAS in the next few years—in fear of litigation."

See if the company you are buying from has released any studies showing whether or not their product contains PFAS. If you don’t see this information publicly available, send them an email and request it, or even request that they conduct such tests in the future.

As the Thinx example shows, not every brand who boasts being free of toxins like PFAS can actually prove it.

What This Means For You

Because of a class action lawsuit regarding PFAS, if you currently wear a Thinx brand, you can submit a claim for up to $7 refund per pair of underwear, for a maximum of three pairs.

1 Source
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Endocrine Society. PFAS chemicals: EDCs contaminating our water and food supply.

By Claire Wolters
Claire Wolters is a staff reporter covering health news for Verywell. She is most passionate about stories that cover real issues and spark change.