PFAS in Period Underwear: What to Avoid and Safer Alternatives (2026)

Several leading period underwear brands tested positive for intentionally added PFAS.

Quick answer

Some period underwear contain PFAS ("forever chemicals") and some do not. Several leading period underwear brands tested positive for intentionally added PFAS. Third-party testing has flagged specific brands (below); safer options include Aisle period underwear – Mamavation-verified PFAS-free and Saalt period underwear – third-party tested PFAS-free. The same chemicals contaminate drinking water, so the highest-impact step for most people is filtering their tap.

How we source this: we report published third-party testing (Green Science Policy Institute, Consumer Reports, Mamavation, Ecology Center, Silent Spring Institute, and peer-reviewed studies) and name the study behind each finding. We do not test products ourselves.

How PFAS gets into period underwear

Period underwear uses multiple fabric layers including a "leak-resistant" layer. Some manufacturers used PFAS to enhance liquid blocking. The 2020 Sierra Magazine investigation of Thinx found PFAS at the level expected from intentional addition, not contamination.

What testing has found

Sierra Magazine 2020 found PFAS in Thinx period underwear. A class-action lawsuit settled for $5M in 2023 (Thinx denied wrongdoing). Mamavation 2022 expanded testing found PFAS in 65% of period underwear samples across multiple brands including Knix and Modibodi.

Brands flagged in testing

  • Thinx (settled $5M class-action 2023)
  • Knix period underwear (Mamavation 2022 testing)
  • Modibodi (Mamavation 2022 testing)
  • Most generic Amazon period underwear from unknown brands

Safer brand alternatives

  • Aisle period underwear – Mamavation-verified PFAS-free
  • Saalt period underwear – third-party tested PFAS-free
  • Proof – independent PFAS-free verification
  • Reusable cloth pads (Glad Rags, Hannahpad)
  • Switch to a menstrual cup (Saalt, DivaCup) – eliminates the issue entirely

How this connects to your drinking water

Every wash of PFAS-containing period underwear releases PFAS into wastewater, which can't be removed by treatment plants. The PFAS ends up discharged into rivers and oceans.

What to do right now

  • Switch to a menstrual cup – most reliable PFAS-free option, lasts 10+ years
  • For period underwear: choose Aisle, Saalt, or Proof (Mamavation-verified)
  • Check Mamavation's annual menstrual product PFAS lists before buying
  • If you have Thinx – the 2023 settlement provided refunds; check if you're eligible

Frequently asked questions

Do all period underwear contain PFAS?
No. Several brands have been third-party tested PFAS-free, including Aisle period underwear – Mamavation-verified PFAS-free, Saalt period underwear – third-party tested PFAS-free, Proof – independent PFAS-free verification. The PFAS-containing products are usually those marketed with words like "stain-resistant," "waterproof," "long-wear," "non-stick," or "grease-resistant."
How do I know if my period underwear have PFAS?
Check the ingredient list or product spec sheet for: PTFE, PFOA, PFOS, perfluoro-, polyfluoro-, fluoro-, or "fluorocarbon" prefixes. If the product is labeled "stain-resistant," "waterproof," or "non-stick" without an explicit PFAS-free certification, assume PFAS until proven otherwise.
What's the safest alternative?
For period underwear, the cleanest options include Aisle period underwear – Mamavation-verified PFAS-free and Saalt period underwear – third-party tested PFAS-free. Switch to a menstrual cup – most reliable PFAS-free option, lasts 10+ years.
How does this connect to drinking water contamination?
Every wash of PFAS-containing period underwear releases PFAS into wastewater, which can't be removed by treatment plants. The PFAS ends up discharged into rivers and oceans.
Are PFAS in period underwear regulated?
Federal regulation is limited. In February 2024 the FDA announced that manufacturers had stopped selling PFAS-based grease-proofing agents for US food packaging, a voluntary phase-out rather than a ban. 13+ US states have passed PFAS-in-products bans (Maine, California, New York, Washington, Minnesota, others). Personal-care PFAS are not federally regulated, though several states are considering bans.