What to Know About PFAS in Period Underwear

Thinx just settled a lawsuit alleging its products contain harmful chemical compounds, raising further questions about the safety of period products overall.

Two pairs of Thinx underwear (one black pair and one nude) on mannequin torsos in a department store. There is a group of women chatting in the background at right, and racks of clothing in the background at left.
Credit...Getty Images

This week, the period underwear brand Thinx made public that it had reached a settlement in a 3-year-long class action lawsuit claiming its products contain harmful chemicals. The news of the settlement brought renewed focus on the chemical compounds at the center of the lawsuit — per- and polyfluoroalkyl substances, known as PFAS or “forever chemicals” — and highlighted the broader issue of toxic ingredients in period products as a whole.

Period underwear are designed to work a little like a traditional menstrual pad in that they can soak up blood but, unlike a disposable pad, the underwear can be washed and reused. The presence of PFAS in Thinx products was first revealed in January 2020, when Sierra magazine published an investigation, in partnership with a researcher at the University of Notre Dame, that found these chemicals in the crotch area of Thinx underwear. Later that year, at least three different lawsuits filed against Thinx included further evidence from third-party testers of PFAS and other toxins in the underwear.

Eventually, a number of the lawsuits consolidated into one class-action case and the company reached a settlement at the end of last year. On Tuesday, consumers could begin applying for refunds for up to three pairs of Thinx underwear: $7 per pair for people who still have receipts and $3.50 for those who don’t (a paltry percentage, as users noted on Twitter, of the $35 that each pair is initially sold for).

In an emailed statement to The New York Times, Thinx wrote that “PFAS has never been part of our product design” and that, going forward, the brand will take measures to ensure the chemicals are not “added to our products.” The settlement, it wrote, “is not an admission of guilt or wrongdoing.”

The crux of those lawsuits, however, is that while PFAS and other environmental toxins are present in a wide range of consumer products, Thinx misled consumers, marketing itself as an “organic, sustainable and nontoxic” alternative to traditional one-use menstrual products, including pads and tampons. The deception, lawyers argued, “renders the Thinx Underwear worthless,” particularly at a time when a growing number of menstruating people — particularly Gen Z consumers — are proactively seeking out safer, more environmentally friendly products.

For parents, the news of the settlement raised concerns about how safe period products are for their kids. “I also purchased a pair of period underwear for my daughter,” said Dr. Shruthi Mahalingaiah, an environmental health researcher at Harvard T.H. Chan School of Public Health who is focused on the impact of environmental toxins on women’s reproductive health. “Scouring for safe products that were branded organic and natural did influence our purchase choices.”

“If I, someone with expertise, still have difficulties identifying what’s safe for my children, I don’t suspect it’s any easier for anyone else,” she added.

Here’s what we know and don’t know about PFAS and the health risks associated with them, particularly when it comes to period products.

PFAS are often called “forever chemicals” because they are practically indestructible. Since the late 1930s, these chemicals have been used in almost every kind of consumer product, including cooking pans, shampoo, cleaning products and cosmetics, to make products resistant to water, oil or heat. They can also be used to make clothing water-resistant — which, the lawsuit claims, is how Thinx underwear manages to absorb period blood and still feel dry.

PFAS may contaminate anything they touch (including food wrapped in packaging containing PFAS) and they do not degrade naturally, nor can our bodies metabolize them, Dr. Mahalingaiah said. Instead, they accumulate in our bodies and in the environment, polluting soil, air and water.

Because these chemical compounds are so inescapable, most people in the United States “have PFAS in the blood,” according to the Agency for Toxic Substances and Disease Registry.

The exposure to PFAS and their accumulation in the body pose several long-term health risks. In 2017, the International Agency for Research on Cancer classified certain PFAS as potential carcinogens. PFAS also disrupt hormonal functions and some research has suggested that they are linked to accelerated ovarian aging, period irregularities and ovarian disorders like polycystic ovarian syndrome.

For pregnant women, PFAS have been associated with an increased risk of high blood pressure, or pre-eclampsia, and some research suggests that babies who are exposed in utero face an increased risk of low birth weight. In a recent study, Dr. Mahalingaiah found PFAS in period blood, which suggests the chemicals can make their way to the reproductive system, presenting a potential risk to uterine function and early pregnancy.

However, the Centers for Disease Control and Prevention cautions that the health impacts of PFAS are still “uncertain” because many of the studies are done on laboratory animals who are exposed to PFA levels that are “higher than the doses people experience from environmental exposure.” The C.D.C. says more research is necessary to understand the human health effects.

One of the main concerns with PFAS in period products is that the vaginal area is extremely sensitive, said Dr. Marianthi-Anna Kioumourtzoglou, an environmental engineer and epidemiologist at Columbia Mailman School of Public Health. In fact, studies have shown that the vaginal canal can be an effective channel for delivering certain medication into the bloodstream because of its highly absorbent nature.

Experts are also concerned about the effects of PFAS during phases when the body is particularly vulnerable, said Dr. Mahalingaiah, such as when someone gets their first period or is pregnant or in menopause transition. During these times, the body and brain undergo major shifts, making them extra sensitive to endocrine disrupters.

What is unclear when it comes to period products, however, is whether PFAS in these products manage to seep into the bloodstream in higher concentrations than they do via other products, like food packaging or shampoo. “The short answer is we don’t know because this is such an understudied topic,” Dr. Kioumourtzoglou said.

It’s hard to know. There has been “a long history of lack of oversight” when it comes to period products, said Dr. Sharra Vostral, a professor of history at Purdue University who has studied the policy, design and approval processes behind menstrual products. In general, she said, they “have not really been fully tested and understood.”

Though menstrual cups, tampons and pads are considered medical devices, the Food and Drug Administration classifies them as low or medium-high risk. Thinx confirmed, in an email to The Times, that it registered its underwear as a medical device. Because of the classification, these products are not subject to rigorous testing, nor do manufacturers need to label all the materials used in them.

It is unclear, then, which period products contain PFAS or other environmental toxins, as well as the concentration of toxins in those products and how much might be absorbed by the body, Dr. Kioumourtzoglou said. An environmental blog, after testing dozens of products in 2022, found PFAS in pads, panty liners and incontinence pads.

Meanwhile, peer-reviewed studies of these products have found inconsistent results. A recent analysis by Dr. Kioumourtzoglou and several colleagues examined nearly two dozen studies; some studies found significant amounts of an array of toxins in period products and others found only trace amounts that present “low risk to health,” leading the authors to conclude that further research is needed.

When it comes to period underwear, some experts suggest that PFAS might be washed away after a few runs through the laundry, but there isn’t scientific research to confirm that. And studies have not looked specifically into whether PFAS found in period underwear were absorbed in the body — even the Thinx lawsuit was centered on its marketing and not around any health issues the consumers may have had.

Not all period underwear, however, is created equal. The original Sierra magazine investigation and other product testers have identified some brands that they claim are free of toxins.

Experts also suggest using menstrual cups that are made of medical-grade silicone, which Dr. Mahalingaiah said is likely to be “inert.”

“I hope we will see innovations and new kinds of silicone-based products,” she added.