In January 2023, Thinx – the company that made period underwear mainstream – agreed to pay up to $5 million to settle a class action alleging its products contained PFAS despite being marketed as organic, sustainable, and free of harmful chemicals. The company denied wrongdoing in the settlement. But the case started with independent lab work: testing commissioned for a 2020 Sierra magazine report, run by University of Notre Dame physicist Graham Peaslee, found elevated fluorine levels in Thinx layers – the standard screening indicator for intentionally added PFAS.
That case is why "PFAS in period underwear" became a search term at all. And it raises the obvious questions: why would forever chemicals be in underwear, is it actually a health risk, and how do you buy a pair that doesn't have them?
Period underwear works by layering fabrics: a moisture-wicking layer, an absorbent core, and a leak-resistant outer barrier. PFAS chemistry is extremely good at making textiles repel water and resist stains, which is exactly what a leak barrier is supposed to do. That's the same reason PFAS shows up in rain jackets and stain-resistant furniture. In some cases the chemicals probably arrive unintentionally, through treated components in the supply chain rather than a deliberate formula.
The concern with this particular product category is contact: absorbent underwear sits against highly permeable tissue for hours at a time, month after month. To be straight about the science – dermal (skin) absorption of PFAS is much less studied than exposure through drinking water and food, and nobody has published outcome data specific to period underwear. Researchers who flagged the issue, including Peaslee, framed it as an avoidable exposure with an unusually sensitive contact site, not a demonstrated harm. Drinking water remains the dominant PFAS exposure route for most Americans, which you can check for your own system by ZIP code.
Two state laws changed the market:
Because brands don't run separate product lines per state, these two markets effectively pushed the whole US category away from intentional PFAS use. Genuine progress. It's also recent enough that older stock, imports, and unintentional contamination are still live issues, which is where independent testing comes in.
Consumer watchdog testing has filled some of the gap regulators left. Mamavation, an advocacy site that commissions total-fluorine screening through EPA-affiliated lab partners, has tested dozens of period underwear products since 2022: some pairs showed detectable organic fluorine and others showed none, with results varying by brand and even by product line within a brand. Treat those results as screening, not gospel. Total fluorine indicates PFAS is probably present but doesn't identify which compound – and note that Mamavation is an advocacy organization, not a regulatory body.
The pattern across all published testing is consistent, though: PFAS in this category is avoidable, because plenty of products test clean.
The same logic applies to other high-contact absorbent products – we cover the broader category in our guide to PFAS in baby products and the consumer products exposure hub.
Our take: if you own period underwear from before the state bans, replace it as budget allows rather than treating it as an emergency – the exposure route is unproven, and stress has health costs too. The higher-leverage move for most households is checking the exposure route with decades of dose data behind it: your tap water. Look up your water system's actual EPA test results, and if PFAS shows up there, a certified filter does more for your total exposure than any underwear swap.
### Did Thinx admit its products contained PFAS? No. Thinx denied wrongdoing; the settlement (up to $5 million, January 2023) resolved the claims without an admission. The underlying fluorine testing was commissioned by journalists and run at Notre Dame.
### Is PFAS in period underwear dangerous? Unknown. Dermal absorption of PFAS is poorly studied compared to ingestion, and no health outcomes have been tied to this product category. Experts describe it as an avoidable exposure at a sensitive contact site.
### Are period underwear sold today PFAS-free? Intentionally added PFAS is now illegal in apparel in New York (since end of 2023) and textiles in California (since 2025), which reshaped the national market. Unintentional contamination can still occur, so brands publishing third-party fluorine testing remain the safer pick.
### Should I throw out my old pairs? If they predate the bans and the brand never published testing, replacing them is reasonable. It's a low-urgency swap, not a crisis.
Last updated July 2, 2026. Sources: Thinx class action settlement (S.D.N.Y., January 2023), Sierra magazine PFAS testing report (2020, testing by Dr. Graham Peaslee, University of Notre Dame), California AB 1817 (2022), New York State PFAS-in-apparel ban, Mamavation consumer testing reports (2022-2025).