Endocrine disruptors are chemicals that interfere with the body's hormonal signaling. They do not need to be present in large quantities to have an effect. They work by mimicking, blocking, or altering the production of hormones, often at very low concentrations, in ways that accumulate over repeated exposures.
The reason this is relevant to activewear is straightforward: the most common chemicals found in synthetic workout clothes, PFAS and phthalates, are both classified as endocrine disruptors. For women choosing non toxic activewear collection options, this is the chemical concern most worth understanding before making a decision.
PFAS and the Hormone System
Per- and polyfluoroalkyl substances (PFAS) are used in the durable water repellent coatings and stain-resistance treatments applied to many synthetic activewear garments. The EPA has documented associations between PFAS exposure and thyroid disruption, immune suppression, altered cholesterol metabolism, and elevated risk of hormone-sensitive cancers based on human epidemiological studies.
Thyroid hormones regulate metabolism, energy, temperature regulation, and reproductive function. PFAS compounds have been shown to compete with thyroid hormones for binding sites on transport proteins, reducing the availability of active thyroid hormone in circulation. This is a mechanism with documented effects in human studies, not just animal models.
The Lululemon investigation made this concrete for the activewear category. In April 2026, the Texas Attorney General opened a civil investigation into Lululemon over PFAS in its products, citing emerging research on associations between synthetic materials in activewear and endocrine disruption, infertility, and cancer. Lululemon confirmed PFAS had been used in its durable water repellent products before being phased out in 2024. The investigation examined whether health-conscious consumers had been misled by wellness-focused branding while these chemicals were present.
Phthalates and Reproductive Hormones
Phthalates are plasticizers used in the manufacture of synthetic polymer fibers and in some printing inks applied to garments. They are classified as endocrine disruptors with particular relevance to reproductive hormone function.
The National Toxicology Program has concluded that several phthalates are reproductive toxicants in animal studies. Human epidemiological research has found associations between phthalate metabolite levels and disruptions to testosterone, estrogen, and thyroid hormone levels. A review published in the International Journal of Hygiene and Environmental Health (Heudorf, U., et al., 2007) summarized phthalate exposure pathways and documented endocrine-disrupting mechanisms across available human and animal data.
Phthalates migrate out of synthetic fabrics over time, particularly under heat and friction. Both are present during exercise. The migration pathway toward skin is established; the dose reaching any individual is variable and difficult to quantify without measurement, but the directionality of the exposure is not in dispute.
Why Activewear Is a Higher-Exposure Category
Chemical exposure through clothing is not uniform across garment types. Activewear is in a higher-exposure category for several compounding reasons.
First, it is worn in direct, full-body contact during physical activity, when skin temperature is elevated and pores are open. Second, it is worn for extended periods, often 60 to 90 minutes or more per session. Third, it is worn repeatedly, meaning exposure accumulates over time rather than occurring once. Fourth, the synthetic fibers and chemical finishes most associated with endocrine disruption are the industry standard in this specific category.
A 2021 analysis in Sustainability examining transdermal microplastic and chemical absorption noted that exercise conditions, specifically sweating and elevated skin temperature, are more favorable for skin absorption than resting conditions. This applies to both microplastic particles and chemical compounds that can leach from synthetic fabrics.
What a Lower-Exposure Choice Looks Like
Reducing chemical exposure through activewear starts with the base fiber. TENCEL Lyocell is a cellulosic fiber, not a synthetic polymer. It does not contain phthalate plasticizers, does not carry a petroleum-derived polymer structure, and does not shed plastic microfibers. Its moisture management is structural: the fiber absorbs moisture into its core, reducing surface humidity and the need for chemical odor-control finishes that introduce additional inputs.
Kaplan et al. (2014), in Fibers and Polymers, documented TENCEL's superior moisture management and thermal comfort performance in active wear applications compared to synthetic alternatives. The fiber carries OEKO-TEX Standard 100 certification, meaning it has been independently tested against a restricted substances list that includes PFAS, phthalates, formaldehyde, and heavy metals.
Bellissima's Sempre Leggings are 92% TENCEL Lyocell and 8% spandex. The 8% spandex is disclosed because the full composition is what matters when the question is chemical exposure, not just the primary fiber.
A Question Worth Taking Seriously
The question of whether activewear affects hormones is not hypothetical. The chemicals most associated with endocrine disruption, PFAS and phthalates, have been present in the activewear category as standard practice. The exposure pathway, skin contact during exercise, is one that favors absorption. The regulatory and legal scrutiny, as seen in the Lululemon investigation, reflects that this has moved from a fringe concern into mainstream public health discussion.
You do not need to accept alarm to engage with the evidence. The evidence is enough on its own. For a broader look at whether leggings specifically affect health, whether leggings are bad for your health covers the full picture. And for a complete evaluation framework for avoiding these chemicals, the non-toxic activewear buying guide covers exactly what to look for.
Sources
Texas Attorney General. (2026, April 13). Attorney General Ken Paxton Launches Investigation into Lululemon Over Potential Presence of Toxic Forever Chemicals in Activewear. texasattorneygeneral.gov.
U.S. Environmental Protection Agency. (2024). Our Current Understanding of the Human Health and Environmental Risks of PFAS. EPA.gov.
National Toxicology Program. (2012). NTP Monograph: Phthalates. US Department of Health and Human Services.
Heudorf, U., et al. (2007). Phthalates: Toxicology and exposure. International Journal of Hygiene and Environmental Health, 210(5).
Kaplan, S., et al. (2014). Thermal comfort of lyocell and other fibers in active wear. Fibers and Polymers, 15(6).
OEKO-TEX Association. (2024). OEKO-TEX Standard 100 Testing Criteria. oeko-tex.com.
