The clothes you sweat in are supposed to support your performance. What they may also be doing, according to independent laboratory testing, is exposing you to a hormone-disrupting chemical at levels that far exceed legal safety thresholds.
In 2022 and 2023, the Center for Environmental Health (CEH), a nonprofit that uses chemical testing and litigation to push toxic substances out of consumer products, tested activewear from dozens of major brands and found elevated levels of bisphenol A (BPA) across the board. In one round of testing, leggings, shorts, sports bras, and athletic shirts were found to expose wearers to BPA at up to 40 times the safe limit under California's Proposition 65. That limit, set at 3 micrograms of BPA per day via skin exposure, is not arbitrary -- it's the threshold above which the state requires a cancer and reproductive harm warning on product labels.
BPA ends up in activewear because of how synthetic fabrics are made.
BPA is a synthetic chemical used in the manufacturing of polycarbonate plastics and epoxy resins. It is also used to coat the fibers of polyester and spandex -- the same materials that make leggings stretchy and sports bras supportive. The coating process strengthens the fabric, but it leaves a residue. When those garments are worn against skin, especially during sweat-producing exercise, that residue can transfer.
Studies have confirmed that BPA is absorbed through skin. Research published in the Annals of Work Exposures and Health found that approximately 25% of BPA on the skin surface can be absorbed within 24 hours. Kaya Allan Sugerman, Illegal Toxic Threats Program Director at CEH, put it plainly: "Studies have shown that BPA can be absorbed through skin and end up in the bloodstream after handling receipt paper for seconds or a few minutes at a time. Sports bras and athletic shirts are worn for hours at a time, and you are meant to sweat in them."
The brands named span the entire activewear market.
CEH's testing and legal action have reached brands across every price point and consumer demographic. Legal notices have been sent to: Nike, Alo Yoga, Athleta, PINK (Victoria's Secret), The North Face, New Balance, Adidas, Patagonia, Champion, Fabletics, Sweaty Betty, Asics, FILA, Kohl's (house brands), Amazon Essentials, Outdoor Voices, Reebok, Mizuno, Beyond Yoga, Free People, Hoka, SoulCycle, Under Armour, and others.
The full list of products flagged includes leggings from Athleta, Champion, Kohl's, Nike, Patagonia, Alo Yoga, Amazon Essentials, Outdoor Voices, and Wilson; sports bras from Nike, Athleta, PINK, Asics, The North Face, All in Motion, FILA, Sweaty Betty, Patagonia, Aerie, and Skechers; and athletic shirts and shorts from brands including Fabletics, Adidas, Champion, Hoka, New Balance, Prana, and Under Armour.
CEH filed lawsuits in California state court against multiple brands beginning in February 2023, using the state's Safe Drinking Water and Toxic Enforcement Act (Proposition 65) as the legal mechanism for enforcement.
BPA is a well-documented endocrine disruptor with serious downstream effects.
BPA was first synthesized in the 1890s as a synthetic estrogen. It mimics the hormone, binding to estrogen receptors throughout the body and interfering with normal hormonal signaling. A foundational review published in Toxicology Letters (PMID: 21605673) described BPA as having "widespread exposure and multiple effects," including reproductive harm, metabolic disruption, and developmental effects at low exposure levels.
The downstream consequences are substantial. Research published in PMC (PMID: PMC9736436) reviewed epidemiological evidence on BPA and female fertility, finding consistent associations between elevated BPA levels and diminished ovarian reserve, delayed menarche, endometriosis risk, and PCOS. A 2025 review (PMC: PMC12206273) specifically examined BPA's impact on reproductive health, finding effects across hormonal regulation, ovarian function, and pregnancy outcomes. Dr. Jimena Diaz Leiva, Science Director at CEH, noted that "even low levels of exposure during pregnancy have been associated with abnormal development of the mammary glands and ovaries that can increase the likelihood of developing breast or ovarian cancer later in life."
Outside of reproduction, BPA has been linked to insulin resistance, early-onset puberty in girls, metabolic syndrome, and cardiovascular disease.
The fitness industry has a transparency problem.
Clothing brands are not required to disclose the chemicals used in fabric manufacturing. BPA does not appear on labels. There is no federal standard for BPA in textiles -- Proposition 65 is a California-specific right-to-know law, and it is one of the only mechanisms consumers currently have to hold brands accountable for what's in their clothes.
CEH has pushed more than 100 companies to reformulate and remove bisphenols from their products since 2021, and some have agreed to do so. But until transparency becomes a baseline expectation rather than a litigation outcome, shoppers have no way to know what's in the leggings they wear to the gym -- or what gets absorbed through their skin while they're in them. The activewear industry has been building product lines on a synthetic material that happens to carry a known hormone disruptor. The question isn't whether that's a problem. It's why it took independent testing and litigation to surface it.
