Georden Jones, Founder, The Peer Review · Last updated: September 2, 2026
The Short Answer
Moisture-wicking, odor-resistant, and “stay-dry” claims on activewear and underwear frequently mean the fabric was treated with PFAS, the same forever-chemical family covered in depth on this site’s PFAS pillar. Two specific cases moved this from a general category concern to a documented one. Thinx, the period underwear brand, settled a class-action lawsuit for up to $5 million after independent lab testing by a Notre Dame PFAS researcher found up to 3,264 parts per million of fluorine in the crotch lining of its underwear, well above the 100 ppm threshold generally considered evidence of intentional addition, with roughly 65% of tested products showing detectable fluorine [1][2]. Separately, a Mamavation and Environmental Health News investigation testing 32 pairs of popular leggings and yoga pants, including Lululemon, found detectable fluorine in one in four pairs, and in April 2026 the Texas Attorney General opened a civil investigation into whether Lululemon’s marketing matched its products’ actual chemical content [3][4]. Lululemon states it phased out intentionally added PFAS starting in fiscal year 2023 [4]. A separate, unrelated concern shows up specifically in “odor-resistant” underwear and socks: antimicrobial silver treatments, which are not PFAS but carry their own early-stage toxicity questions [5][6]. Because the evidence splits between documented, brand-specific PFAS findings and a chemical category (antimicrobial silver) that is Not Enough to Say, this page earns a Mixed Signals rating.
Quick Answer: is my activewear or underwear treated with PFAS?
- Confirmed by lawsuit and lab testing: Thinx underwear (up to 3,264 ppm fluorine, crotch lining) [1][2].
- Confirmed by independent testing, under regulatory investigation: Lululemon and other leggings brands (1 in 4 tested positive) [3][4].
- A different chemical, not PFAS: antimicrobial silver in “odor-resistant” underwear and socks; early toxicity data, not yet a settled health question [5][6].
- How it reaches you: skin contact, concentrated in the crotch and underarm areas where sweat and heat are highest [7][8].
- Evidence Rating: Mixed Signals. PFAS as a chemical family causing health harm is General Consensus (see the PFAS pillar); which specific activewear and underwear brands currently contain it is a fast-moving, brand-by-brand picture, not a category-wide verdict.
Table of Contents
- Identify: Why Performance Fabric Uses PFAS
- Where It Hides
- How It Reaches You
- Investigate: What the Lawsuits and Testing Found
- What Canada, the US, and the EU Require
- Inform: What This Means for You
- Improve: Plastic-Free and PFAS-Free Brands Worth Knowing
- FAQ
- The Bottom Line
- References
Identify: Why Performance Fabric Uses PFAS
“Moisture-wicking,” “stay-dry,” and “odor-resistant” are performance claims, and the easiest, longest-lasting way to deliver them chemically has historically been a PFAS-based finish. The same carbon-fluorine chemistry that keeps a rain jacket waterproof also repels sweat and body oils on a legging or underwear liner, which is why the fabric industry adopted it broadly for close-contact athletic and intimate apparel, not just outerwear [7][9]. This is the same chemical family covered in full on the PFAS pillar: a class of over 4,000 synthetic compounds that resist breakdown, accumulate in the body over time, and are linked by the National Academies and the CDC’s ATSDR to effects including elevated cholesterol, reduced vaccine response, and pregnancy complications [9].
What makes activewear and underwear a distinct case worth its own page, rather than a subset of the general PFAS pillar, is two things: the fabric sits directly against skin in the body’s warmest, sweatiest areas for extended periods, and two specific brands have now been through lab testing and legal proceedings that put real numbers on the question, rather than leaving it as a category-wide guess [1][2][3][4].
Where It Hides
- Period and absorbent underwear liners, specifically the inner crotch layer designed to wick and trap moisture. This is where Thinx testing found its highest fluorine concentrations [1][2].
- Moisture-wicking leggings and yoga pants, particularly styles marketed with “sweat-wicking” or odor control claims. Testing found the crotch area most likely to carry detectable fluorine, consistent with where the finish is applied most heavily [3].
- Durable water-repellent (DWR) outer layers on running jackets and windbreakers, the same treatment category covered in the general PFAS pillar for rain gear [9][10].
- “Odor-resistant” or “anti-microbial” underwear, socks, and base layers. A meaningful share of these use antimicrobial silver (sometimes branded Agion) rather than PFAS specifically, a chemically distinct concern covered in its own section below [5][6][11].
- Compression and seamless athletic wear, where a smooth, snag-resistant finish sometimes doubles as a stain- or moisture-repellent treatment.
How It Reaches You
The exposure route for treated activewear and underwear is skin contact, concentrated specifically in the areas where the fabric sits closest, sweats most, and heats up the most: the crotch, waistband, and underarms [7][8]. Sweat and body heat are known to mobilize surface-applied chemical finishes, and PFAS applied as a fabric treatment sits on and within the fibre surface rather than being chemically bonded into the material forever, so it can transfer to skin over the course of wear [7][8]. The general PFAS pillar covers the fuller dermal-absorption picture: research shows meaningful skin absorption for some PFAS in their neutral chemical form, while ionic forms (more common in older, weathered treatments) show more limited and chemical-specific absorption, so “PFAS in the fabric” and “PFAS in your bloodstream” are related but not identical claims [9].
Beyond direct skin transfer, washing treated activewear releases PFAS into wastewater, and normal wear and laundering gradually break down the treatment, both a personal exposure question and an environmental one [10].
Investigate: What the Lawsuits and Testing Found
1. Thinx period underwear (settled, strongest documented case). Independent testing by Graham Peaslee, a University of Notre Dame physics professor specializing in PFAS analysis, found fluorine levels of 3,264 ppm in one Thinx product and 2,053 ppm in another, dramatically above the roughly 100 ppm threshold generally treated as evidence of intentional PFAS addition rather than incidental contamination [1]. Around 65% of the Thinx products tested showed detectable fluorine, concentrated specifically in the inner layers of the crotch area [1]. Thinx settled the resulting class-action lawsuit for up to $5 million while denying wrongdoing, and as part of the settlement agreed to stop intentionally adding PFAS and to disclose its use of antimicrobial treatments, including Agion, on its website [1][2].
2. Lululemon and the broader leggings market (ongoing investigation, weaker but real signal). A Mamavation investigation conducted with Environmental Health News tested 32 pairs of popular leggings and yoga pants from an EPA-certified lab and found detectable organic fluorine, a marker for PFAS, in about one in four pairs, at levels ranging from 10 to 284 ppm [3]. Lululemon products were among those flagged, with one Align Highrise Pant testing at 32 ppm concentrated in the crotch area, while other styles in the same test showed no detectable fluorine, underscoring that this is a product-by-product finding rather than a brand-wide certainty [3]. In April 2026, the Texas Attorney General’s office issued a civil investigative demand to Lululemon examining whether its marketing claims matched its products’ actual chemical content; Lululemon states it phased out intentionally added PFAS starting in fiscal year 2023 and is cooperating with the inquiry [4].
3. Antimicrobial silver in “odor-resistant” underwear and socks (a different chemical, still unsettled). Silver nanoparticles and silver-ion treatments, sometimes sold under the brand name Agion, are used to kill odor-causing bacteria in performance fabric, and this is chemically unrelated to PFAS, not a synonym for it [5][11]. Testing has found silver-treated socks can contain up to 1,360 micrograms of silver per gram of fabric and release measurable silver into water on contact [5]. Laboratory research has found silver nanoparticles can be cytotoxic to human cell lines in a dose- and size-dependent way, particularly at very small particle sizes, and can cross the blood-brain barrier in animal studies, while ingested silver is linked to argyria, a benign but permanent blue-grey skin discoloration [6]. None of this constitutes proof of harm from wearing treated underwear or socks under normal conditions. It is an early-stage toxicology picture, not a consensus health finding, which is why this specific exposure earns a Not Enough to Say verdict distinct from the more documented PFAS cases above [5][6].
What Canada, the US, and the EU Require
| Requirement | Canada | United States | European Union |
|---|---|---|---|
| Textile-specific PFAS restriction | None currently; PFAS as a class is proposed for addition to the toxic substances list under CEPA, with textiles slated for a later regulatory phase after firefighting foam [9] | No federal textile-specific rule; California (AB 1817) and New York (S.1322/A.994) both ban intentionally added PFAS in apparel, effective January 2025 [12][13] | No dedicated textile ban yet in force; a broad PFAS restriction proposal is under ECHA review that would eventually cover textiles among many product categories |
| Disclosure of antimicrobial treatments (e.g., silver, Agion) | No specific requirement | No federal requirement; Thinx’s 2022 settlement created a company-specific disclosure obligation, not an industry-wide rule [1][2] | No specific requirement |
| Enforcement mechanism used so far | None yet for textiles specifically | State attorney general investigation (Texas, Lululemon, opened April 2026) and private class-action litigation (Thinx) [1][4] | Regulatory proposal stage; no textile enforcement action yet |
| General PFAS regulatory posture | Precautionary, class-based (30 ng/L combined drinking water objective; broader toxic-substances listing proposed) [9] | Substance-by-substance (enforceable limits for PFOA/PFOS in water; state-level textile bans filling the federal gap) [9][12][13] | Moving toward the broadest single restriction proposal of the three, though not yet finalized for textiles specifically |
The clearest pattern: litigation and state-level action, not federal rulemaking, is what has moved the needle on PFAS in activewear and underwear so far, in both documented cases covered above. California and New York’s textile-specific bans are the first laws anywhere in North America written for this exact product category, and they only took effect in January 2025 [12][13].
Inform: What This Means for You
- Two specific brands have documented findings, not the entire category. Thinx has a settled lawsuit and disclosed testing results; Lululemon is under active investigation with mixed test results across its own product line. Neither finding means every legging or every pair of underwear on the market is PFAS-treated [1][2][3][4].
- “Odor-resistant” is a different claim than “moisture-wicking.” The first often points to antimicrobial silver, the second more often to a PFAS-based finish. They are separate chemistries with separate, and separately uncertain, safety questions [5][9].
- The crotch and underarm areas are where testing consistently finds the highest concentrations, which tracks with where these finishes are applied most heavily and where skin contact, heat, and sweat are greatest [1][3][7].
- State law, not federal regulation, currently sets the floor. California and New York ban intentionally added PFAS in apparel; most of the rest of North America does not yet have an equivalent rule [12][13].
- Brand statements that PFAS was “phased out” describe a policy going forward, not a guarantee about products already on shelves or already in your drawer [4].
Improve: Plastic-Free and PFAS-Free Brands Worth Knowing
For readers who would rather sidestep the PFAS and antimicrobial-silver question in performance and intimate apparel entirely, a real, expanding market of natural-fibre brands does this by design, using organic cotton, merino wool, alpaca, or TENCEL instead of synthetic performance finishes:
- For activewear: Wayve, Nero, and Ryker each build performance pieces from organic cotton and merino wool blends rather than polyester and PFAS-based finishes. Icebreaker relies on merino wool specifically for its moisture and odor management, achieved through the fibre’s natural properties rather than an added chemical treatment. Tripulse and Paka both build around TENCEL, with Paka adding alpaca wool, aiming for the same performance claims (moisture management, odor resistance) through fibre choice instead of finish chemistry.
- For underwear: KENT makes underwear from 100% GOTS-certified organic cotton with no synthetic fibres, PFAS, or plastic dyes, and discloses its full material sourcing. Cottonique builds allergy-focused, latex- and spandex-free organic cotton underwear using a patented hydrothermal finishing process instead of chemical treatments, and has published double-blind testing on symptom improvement for chemically sensitive wearers.
- The trade-off worth knowing upfront: natural-fibre performance wear generally costs more and may not match synthetic fabric’s stretch, quick-dry speed, or exact odor control under heavy, repeated athletic use. That is a genuine functional trade-off, not a reason to dismiss the category, and it is worth weighing against how often you need peak synthetic performance versus everyday wear.
- Read the label, not just the marketing claim. “Sustainable” and “eco” language does not guarantee PFAS-free, but “PFAS-free,” “fluorine-free,” or a full material disclosure on the brand’s own site does [10].
FAQ
Does all activewear contain PFAS?
No. Independent testing found detectable fluorine in about one in four tested leggings, not all of them, and results varied even within the same brand’s product line [3]. The safest assumption is product-specific, not brand-wide or category-wide.
Is Thinx underwear still sold with PFAS in it?
As part of its 2022 class-action settlement, Thinx agreed to stop intentionally adding PFAS and to disclose its antimicrobial treatments going forward, but the settlement does not retroactively change products already purchased before that change [1][2].
Is antimicrobial silver in odor-resistant underwear the same thing as PFAS?
No, and this is a common mix-up. Silver-based antimicrobial treatments are a chemically different category from PFAS, with their own, separate and still-developing toxicity questions rather than the PFAS-specific evidence base [5][6].
Which states or countries ban PFAS in clothing?
California (AB 1817) and New York (S.1322/A.994) both ban intentionally added PFAS in apparel, effective January 2025. No federal US law, Canadian law, or EU law currently imposes an equivalent textile-specific ban [9][12][13].
What should I look for if I want PFAS-free activewear or underwear?
Natural-fibre brands built around organic cotton, merino wool, alpaca, or TENCEL, such as Wayve, Nero, Ryker, Icebreaker, Tripulse, Paka, KENT, and Cottonique, achieve performance claims through fibre choice rather than chemical finishes. Look for explicit “PFAS-free” language or full material disclosure rather than general “sustainable” marketing [10].
The Bottom Line
PFAS in activewear and underwear moved from a general category concern to a documented one through two specific cases: Thinx’s settled $5 million lawsuit, backed by lab testing that found fluorine levels dramatically above the threshold for intentional addition, and the ongoing Texas Attorney General investigation into Lululemon, prompted by independent testing that found detectable PFAS in about a quarter of tested leggings [1][2][3][4]. A separate, chemically distinct concern, antimicrobial silver in “odor-resistant” products, carries its own early-stage toxicity questions that remain unsettled rather than confirmed [5][6]. California and New York now legally require PFAS-free apparel; most other jurisdictions do not yet [12][13]. If you would rather not wait for the rest of the market to catch up, organic cotton, merino wool, alpaca, and TENCEL brands deliver comparable performance claims without the chemistry in question, at the cost of a real, worth-knowing trade-off in price and synthetic-level stretch or dry time.
Stay curious, stay critical.
Georden
References
- “PFAS Class-Action Thinx Period Underwear Lawsuit Settled for $5 Million.” ConsumerNotice.org.
- “Thinx Settles Class Action Lawsuit While Knix Fights Back.” WWD/Sourcing Journal.
- “Investigation finds evidence of PFAS in workout and yoga pants.” Environmental Health News (EHN).
- “Toxic Indications of PFAS ‘Forever Chemicals’ In My Lululemon Activewear Pants.” Mamavation.
- “Antibacterial and yellowing performances of sports underwear fabric with polyamide/silver ion polyurethane filaments.” De Gruyter, AUTEX Research Journal.
- “Evaluation of Silver Nanoparticle Toxicity in Skin in Vivo and Keratinocytes in Vitro.” PMC.
- “The effect of weathering on per- and polyfluoroalkyl substances (PFASs) from durable water repellent (DWR) clothing.” ScienceDirect.
- “Fate of Per- and Polyfluoroalkyl Substances from Durable Water-Repellent Clothing during Use.” Environmental Science & Technology / PMC.
- “PFAS (‘Forever Chemicals’): Where They Actually Hide and How They Get Into You.” The Peer Review.
- “PFAS in Clothing: 2026 Bans, Health Risks, and Safer Alternatives.” bluesign.
- “Are Your Gym Clothes Toxic? PFAS, BPA & Hidden Chemicals in Activewear.” FiberCheck.
- “How to Avoid PFAS in Clothing: Practical Tips.” Tripulse.
- “10 PFAS-Free Apparel Brands For Nontoxic Clothing (2026).” The Good Trade.
Georden Jones is the founder of The Peer Review. Read the full story.