If you live in the U.S. and bought Thinx underwear recently, you could soon be getting some money back.

That's because the period panty brand has just settled a class-action lawsuit alleging that its products — long marketed as a safer, more sustainable approach to menstrual hygiene — contain potentially harmful chemicals.

Plaintiffs say third-party testing on the underwear revealed the presence of short chain per-and polyfluoroalkyl substances (PFAS), human-made chemicals that are found in many consumer and industrial products, do not easily break down and have been linked to adverse health effects. And they're accusing the company of fraud and other deceptive practices as a result.

"Through its uniform, widespread, nationwide advertising campaign, [Thinx] has led consumers to believe that Thinx Underwear is a safe, healthy and sustainable choice for women, and that it is free of harmful chemicals," the complaint filed in May 2022 said. "In reality, Thinx Underwear contains harmful chemicals ... which are a safety hazard to the female body and the environment."

Thinx denies those allegations, with a company spokesperson telling NPR in an email that PFAS have never been part of its product design and that it will continue to take measures to ensure the chemicals are not added to its products.

"The litigation against Thinx has been resolved, the settlement is not an admission of guilt or wrongdoing by Thinx, and we deny all allegations made in the lawsuit," the spokesperson added.

The U.S. District Court for the Southern District of New York gave the settlement its preliminary approval in December, more than two years after the litigation began (this case combines two existing lawsuits filed in Massachusetts and California).

Class members were notified of the settlement this week. As part of it, Thinx has committed to paying up to $5 million to provide reimbursement as well as making some changes to its marketing and production processes.

Anyone who bought Thinx underwear between Nov. 12, 2016, and Nov. 28, 2022, can submit a claim online before mid-April to choose between cash reimbursement for up to three pairs of purchased underwear at $7 each or a voucher for 35% off a single purchase of up to $150 (for a maximum discount of $52.50).

Thinx will also take steps to ensure that PFAS are not intentionally added to its underwear at any stage of production and adjust some of its marketing language, including disclosing the use of antimicrobial treatments. It will also continue to have suppliers of raw materials sign a code of conduct and agreement attesting that PFAS are not being intentionally added to Thinx underwear.

Erin Ruben, an attorney who represents several of the plaintiffs, told NPR in a phone interview that she and her clients are pleased with the terms of the settlement and happy that the case has brought awareness to the issue of PFAS in consumer products.

"When consumers demand transparency related to these issues, I think that businesses have no choice but to listen," Ruben added. "And so it's my hope that as consumers become more aware of the chemicals that are present in the products that they use every day, that they use their voice to let businesses know that it's not something that they want."

The lawsuit doesn't accuse the product of causing harm

Ruben stresses that the case is about the way Thinx marketed its product, not the potential health effects of it.

"The plaintiffs in this case brought their claims because ... the presence of PFAS or other chemicals in the underwear would influence their purchasing decision," she said. "This case is centered on marketing concerns, and did not allege any claims related to personal injury resulting from the product."

The lawsuit alleges that Thinx uses PFAS chemicals to "enhance the performance of the underwear, including, but not limited to, its 'moisture-wicking' and 'leak-resisting' qualities."

It explains that the thousands of PFAS chemicals in existence are all categorized either as "long-chain" or "short-chain," based on whether they contain fewer or more than eight carbon atoms.

Long-chain chemicals — sometimes called "forever chemicals" — have been known to cause negative health effects and have been phased out of use in the U.S., the suit says, adding that short-chain chemicals are being used as replacements in the apparel industry.

That's despite the fact that there are no long-term studies to show whether they are any safer for consumers, and that there is even some evidence of them posing similar health risks, it says. And the use of PFAS also contradicts the company's own advertisements for its products, the plaintiffs allege.

According to the complaint, Thinx said in multiple places on its website that its underwear was rigorously tested and free of harmful chemicals, even claiming that the chemical compounds used in its anti-odor layer "stay on the surface of the underwear and don't travel into your body."

Those claims were repeatedly disputed, however (and vanished from its website around May 2021, according to the lawsuit).

In 2020, reporter Jessian Choy sent several pairs of Thinx underwear to a University of Notre Dame laboratory, which found high levels of fluorine and concluded that the underwear contained PFAS. She detailed those findings in an article for Sierra (the Sierra Club magazine).

Then-Thinx CEO Maria Molland released a statement after the article's publication reiterating the company's strict testing standards. Molland said the company had engaged a toxicologist to review those findings, who confirmed there were "no detectable long-chain PFAS chemicals" in the products (the lawsuit alleges that statement misrepresented the testing and results, further misleading customers).

Nicole Dickens, the plaintiff who first filed the New York complaint, heard about reports of chemicals in Thinx underwear around November 2020, court documents say. She stopped buying the underwear and sought independent third-party testing, which found "short-chain PFAS chemicals in Thinx underwear at material and above trace amounts."

A growing body of research links PFAS exposure to health effects

PFAS have been used in consumer and industry products since the 1940s, appearing in things like nonstick cookware, water repellent clothing, some firefighting foams and certain cosmetics.

People can be exposed to PFAS in a variety of ways, including by drinking contaminated water and eating food that's either grown near places that use PFAS or packaged in material that contains them.

PFAS can get into soil, water and air during production and use, and because those chemicals do not break down, they remain in the environment.

"Because of their widespread use and their persistence in the environment, PFAS are found in the blood of people and animals all over the world and are present at low levels in a variety of food products and in the environment. Some PFAS can build up in people and animals with repeated exposure over time," the Centers for Disease Control and Prevention says.

Scientists are still working to understand the exact effects of PFAS exposure, but a growing body of evidence is linking it to harmful health outcomes.

Studies suggest that high levels of certain PFAS may lead to increased cholesterol levels, changes in liver enzymes, decreases in infant birth weights, increased risk of high blood pressure in pregnant people and increased risk of kidney or testicular cancer, according to the CDC's Agency for Toxic Substances and Disease Registry.

The CDC has also recognized that high levels of exposure may impact the immune system by suppressing the antibody response to vaccines — of particular concern during a global pandemic — and is working to understand how exposure may affect illness from COVID-19.

If you've been exposed to PFAS and are concerned about your health, the CDC suggests speaking to your doctor or taking a blood test, but cautions that it's "unclear what the results mean in terms of possible health effects."

What happens next?

This is the window of time where consumers can learn about the settlement and decide whether they want to be a part of it, Ruben explains.

They can either make a claim for reimbursement or exclude themselves from the class, if they want to opt out of the settlement and pursue their own individual case at a later time.

The advantage of joining a class-action settlement is that it doesn't come at any cost to consumers — whereas someone looking to litigate on an individual basis would have to retain an attorney and go through that process again, Ruben says.

It's not clear how many members are in the class, though the May complaint says "at least thousands" of people could be affected nationwide.

Ruben says lawyers will find out just how many people have made claims under the settlement sometime before the hearing for final approval, which is scheduled for May 24.

Ruben is working on other cases related to PFAS in products and thinks it will be a continued area of practice.

"I think that it's showing no signs of slowing down because ... consumers are expressing to us that they really do care about these issues," she adds.