You buy workout clothes to support your health. The assumption built into that purchase is that the clothes themselves are neutral, a vehicle for movement and nothing more. That assumption is worth examining.
The evidence that has accumulated over the past decade on synthetic activewear, the microplastics it sheds, the chemicals it carries, and the conditions under which it transfers both toward the body, makes a coherent case that for people exercising regularly in synthetic workout clothes, the garments are not a neutral variable. They are an active one.
The Exposure Is Highest When You Think You Are at Your Healthiest
Exercise creates the conditions that maximize chemical and microplastic absorption from synthetic clothing simultaneously. Skin temperature rises. Pores open. Sweating creates a moist interface between fabric and skin that accelerates the migration of chemical compounds from synthetic fiber surfaces toward the body. Inhalation rate increases five to ten times above resting levels, drawing in the microplastic fibers that synthetic activewear sheds continuously during movement.
A 2021 analysis in Sustainability examining transdermal absorption from synthetic textiles found that exercise conditions are more favorable for dermal uptake than resting conditions. The period of highest chemical and microplastic exposure from workout clothes is not when you are sitting in them after a class. It is during the class itself.
What Synthetic Workout Clothes Are Actually Made Of
Polyester, nylon, and spandex are the dominant fibers in the activewear market. All three are petroleum-derived synthetic polymers. Polyester is polyethylene terephthalate, the same polymer as a plastic bottle. Nylon is a polyamide. Spandex is a polyurethane-polyurea copolymer. These are not natural materials that happen to be woven into fabric. They are plastics in fiber form.
As plastics, they shed plastic particles. Browne et al. (2011), in Environmental Science and Technology, established the direct link between synthetic textile washing and microplastic contamination in marine environments. Napper and Thompson (2016), in Marine Pollution Bulletin, quantified shedding from synthetic fabrics under standard washing conditions. The shedding during wear, through friction and movement, has also been documented. For activewear, worn during high-movement, high-friction activity pressed against the skin, the shedding is continuous throughout the workout.
The Chemical Load Beyond the Fiber
The fiber is the starting point, not the complete picture. By the time synthetic activewear reaches you, it has typically been dyed, finished, and treated with chemical inputs that are not disclosed on the fiber content label.
PFAS, used in durable water repellent coatings and stain-resistance treatments, were confirmed as standard practice in the activewear industry through the Texas Attorney General's 2026 investigation into Lululemon. Lululemon acknowledged PFAS had been used in its DWR products through early 2024. The EPA has linked PFAS to thyroid disruption, immune suppression, reduced fertility, and elevated cancer risk. Phthalates, present in synthetic polymer manufacturing, are endocrine disruptors associated with disruptions to reproductive hormone function in human epidemiological studies. Formaldehyde, used in some wrinkle-resistance and shape-retention finishes, is classified as a human carcinogen by the IARC.
None of these appear on the label. The label lists the fiber. The rest is invisible to the buyer.
Where the Evidence Points on Health Effects
The research has moved from environmental documentation into human tissue. Leslie et al. (2022), in Environment International, detected microplastic particles in human blood. Jenner et al. (2022), in Science of the Total Environment, identified microplastic fibers in human lung tissue. Ragusa et al. (2021), in Environment International, found microplastic particles in human placental tissue. Marfella et al. (2024), in the New England Journal of Medicine, found microplastic particles in carotid artery plaque and associated their presence with significantly higher rates of cardiovascular events over the follow-up period.
The specific contribution of activewear to those findings has not been isolated in controlled human studies. What has been established is that the particles are in human tissue, that synthetic textiles are a primary source of the particle types detected, and that the exposure conditions of exercise are among the most favorable for both shedding and absorption.
The Bacterial Problem That Compounds Everything
Synthetic activewear has a secondary health-relevant property that is less discussed than microplastics and chemical finishing: it creates a bacterial environment. Because polyester and nylon are hydrophobic, sweat accumulates on the fabric surface rather than being absorbed. That warm, moist surface is ideal for bacterial growth. Research by Callewaert et al. (2014) in Applied and Environmental Microbiology found that synthetic fabrics retain significantly more odor-causing bacteria after washing than natural fiber alternatives, with bacterial colonization building with each wear cycle.
For the perineal area specifically, sustained warmth, moisture, and bacterial load from synthetic leggings worn during and after exercise create conditions associated with increased risk of yeast infections and UTIs. These are not rare outcomes in the population of people who exercise regularly in synthetic activewear.
What Choosing Differently Actually Changes
TENCEL Lyocell is not a synthetic polymer. It is a cellulosic fiber derived from wood pulp, processed in a closed-loop system with a non-toxic solvent. It does not carry phthalate plasticizers, does not require PFAS-based finishing to manage moisture, and does not shed petroleum-derived plastic microfibers. Its moisture management is structural: it absorbs sweat into the fiber's core rather than leaving it at the surface, reducing bacterial growth conditions and the sweat-mediated chemical migration pathway simultaneously.
Kaplan et al. (2014), in Fibers and Polymers, documented TENCEL's moisture management and thermal comfort advantages in active wear. The Sempre Leggings are 92% TENCEL Lyocell, certified to OEKO-TEX Standard 100. The 8% spandex is stated because the full composition is the relevant information.
The Reasonable Conclusion
The claim is not that your synthetic workout clothes are definitely making you sick. The claim is that the evidence is sufficient to take seriously, that the exposures are real and documented in human tissue, that the conditions of exercise maximize those exposures, and that the fiber in your workout clothes is one of the few variables in this picture that is entirely within your control.
Most people choosing synthetic activewear are doing so without any of this information. That is not a failure of judgment. It is a failure of disclosure. The industry has not told this story. The research has been telling it for over a decade.
Sources
Browne, M.A., et al. (2011). Accumulation of microplastic on shorelines worldwide: sources and sinks. Environmental Science and Technology, 45(21).
Napper, I.E., and Thompson, R.C. (2016). Release of synthetic microplastic plastic fibres from domestic washing machines. Marine Pollution Bulletin, 112(1-2).
Leslie, H.A., et al. (2022). Discovery and quantification of plastic particle pollution in human blood. Environment International, 163.
Jenner, L.C., et al. (2022). Detection of microplastics in human lung tissue using muFTIR spectroscopy. Science of the Total Environment, 831.
Ragusa, A., et al. (2021). Plasticenta: First evidence of microplastics in human placenta. Environment International, 146.
Marfella, R., et al. (2024). Microplastics and nanoplastics in atheromas and cardiovascular events. New England Journal of Medicine, 390(10).
Callewaert, C., et al. (2014). Microbial odor profile of polyester and cotton clothes after a standardized washing procedure. Applied and Environmental Microbiology, 80(23).
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.
Kaplan, S., et al. (2014). Thermal comfort of lyocell and other fibers in active wear. Fibers and Polymers, 15(6).
