Period underwear — that is, underwear with extra layers built in to absorb and wick away menstrual blood — have become a total game-changer when it comes to convenience and ease of use. Whether you've had your Period for decades or your tweens and teens are using them for their first periods, these underwear provide the kind of reassurance that brings any period-haver peace of mind.

The sustainability and freedom from irritating chemicals of period underwear (or period panties — whatever term you prefer) might be an added bonus, especially since they help reduce waste caused by single-use, disposable options like tampons, pads, and panty liners. But apparently, some of the most popular brands of period underwear have been found to contain potentially toxic chemicals, low-key defeating the reason some users prefer them over traditional period products in the first place.

But before you toss those pricey, beloved period undies and curse the patriarchy for its lack of safe, convenient menstrual essentials, keep reading for the scoop on this situation. Scary Mommy asked two menstrual health pros for insight, including why these underwear contain chemicals in the first place and what you should do to stay safe.

How was this even discovered?

Back in January 2020, Sierra first reported that when a nuclear scientist tested Thinx period underwear, they discovered high levels of a group of chemicals called PFAS in several pairs. PFAS (short for per- and polyfluoroalkyl substances) are actually commonly used in many items you probably use or are around daily, including food wrappers, water-repellent fabrics, cleaning products, and paints. PFAS take years to break down in the environment and in the body. Despite their prevalence, they're also linked to a number of health problems, including cancer and decreased fertility, which is why you probably don't want them in direct contact with your vulva and/or vagina.

Thinx faced a class-action lawsuit in 2021 by plaintiffs in Massachusetts. That same year, independent researchers with Mamavation found that of the 21 period underwear brands they tested, only seven were found to be free of PFAS chemicals. Some popular brands with notable levels included Thinx, Cora, Knix, and Proof.

In April 2022, two California women sued Knix Wear, for claiming that despite marketing their period undies as "PFAS-free" and "designed to be both safe and effective," that they, too, contained these icky "forever chemicals." The revelation has also picked up steam on social media, with users confused and dismayed by these reports.

Why does period underwear contain chemicals anyway?

If you're also confused, it's understandable, particularly if you're concerned about your health during your menstrual cycle and beyond. "Traditional period products like tampons, pads, and panty liners are known to contain chemicals like plasticizers and parabens, for preservation and fragrance purposes," says Erin Flynn, DNP/FNP, at Favor. "While these chemicals are common, they can be harmful in certain quantities — some of the chemicals in period products are known as endocrine-disrupting chemicals, which, when absorbed by the vagina (a highly absorptive organ), can lead to endometriosis, tumors, and other endocrine concerns."

"Manufacturers include these chemical additives to maximize absorption/comfort and minimize odor, but less attention is paid to how these chemical exposures might affect the unique and sensitive vaginal and vulvar area, which is very different from other skin on our bodies," adds Alexandra Scranton, the director of science and research at Women's Voices for the Earth.

As for why reusable (and reportedly more eco-friendly) period panties have chemicals like PFAS, Flynn notes that these chemicals "are often used for their stain- and water-resistant qualities, which is likely why some period underwear brands include them in their products."

"It is also possible that PFAS chemicals may be included in some textile dyes," adds Scranton. "Period underwear companies have generally claimed that they do not intentionally add PFAS to these products, so it may be the PFAS that is detected comes from some kind of contamination of one of the other intended ingredients — more research is needed on this."

And therein lies the problem.

Why isn’t more known about this?

Blame the patriarchy. Menstrual health and safety have hardly been at the forefront of research, funding, and general experts' concerns, which explains why there's little concrete research on the matter — despite the fact these chemicals are known irritants and exposure to even small amounts can cause serious health concerns. "PFAS chemicals can be dangerous because it takes a long time for them to break down, and can lead to harmful health effects like liver damage, infertility, and thyroid disease," says Flynn. "Given the vagina's high rate of absorption, these harmful chemicals pose a particular risk in period products."

"There is almost no research on the health effects of using menstrual products," says Scranton. "Manufacturers sometimes do limited irritation studies, but we simply don't know if the chemical exposures from menstrual products are causing other kinds of harm. Certainly, there are some chemicals — like those found in fragrances — that are unnecessary in menstrual products and which can potentially be harmful."

"That said, with more studies emerging about the impacts of PFAS on the body (especially in products that are in very close proximity to your body, like period underwear), it's clear that even where regulations exist, they're often not sufficiently enforced — lack of regulation plays a role," adds Flynn.

Lack of menstrual education in general doesn't help, given that the average period-haver likely has no idea there are potentially harmful additives in their choice of period products, even those labeled "organic" or "eco-friendly." Scranton notes that there's "certainly no guidance on how to ensure the vaginal and vulvar exposure of these chemicals is not harmful. And as mentioned before, there is little research to better understand these exposures and the symptoms and conditions they may be causing. A lack of research does not mean a lack of harm — it just means we haven't investigated to find out. Historically research on vaginal and vulvar issues is rarely done and not well funded."

How do you find safe period underwear?

Before you toss your beloved period panties in a fit of rage, you have options, provided you do a little bit of research. "Look into recent lawsuits to see if your brand of period underwear has come under fire for its usage of PFAS chemicals," says Flynn. "The Environmental Working Group also has a free database called Skin Deep which can help you find out about the chemicals in all of your products."

"It is worth contacting the manufacturer to ask what they make their period underwear from and what kind of additives are added," says Scranton. "Additives that are 'anti-bacterial' can be a red flag as they often have toxic properties."

Though the Food and Drug Administration does not currently regulate period underwear, Scranton notes that New York is the first and only state to now require period products to have ingredients on the label, and California has passed a similar "right to know" law, which will take effect in 2023. That said, Mamavation found a few popular brands to be as close to toxin-free as possible, including Modibodi, Period, Aisle (FKA Lunapads), and Revol. RubyLove is another safe, size-inclusive option as well.

Expert Sources:

Erin Flynn, DNP/FNP, at Favor

Alexandra Scranton, the director of science and research at Women's Voices for the Earth