Every time you wear synthetic workout clothes, they shed. Every time you wash them, they shed more. The fibers that come off are microplastics, and they end up in your body, your home, and the water supply.
This is not a fringe concern. It is one of the most consistently documented findings in textile environmental research over the past fifteen years, and the evidence on where those microplastics go has moved from environmental studies into human tissue research.
What Microplastic Shedding from Workout Clothes Actually Means
Synthetic activewear is made primarily from polyester, nylon, and spandex, all of which are petroleum-derived polymer fibers. When these fabrics are stretched, compressed, or agitated, individual fibers and fiber fragments break free from the fabric surface. These fragments are classified as microplastic microfibers when they measure less than five millimeters, and they are typically far smaller than that.
Browne et al. (2011), writing in Environmental Science and Technology, was among the first to document synthetic microfibers in marine sediment samples across six continents and link them directly to domestic textile washing. That study established washing as a primary release pathway, but it was not the only one.
Subsequent research documented shedding during wear as well. Mechanical stress, including the friction between fabric and skin during movement, causes fiber release throughout the time the garment is worn. For workout clothes, worn during high-movement, high-friction activity in direct contact with the body, the shedding that occurs during wear is not negligible.
How Much Shedding Occurs
Napper and Thompson (2016), in Marine Pollution Bulletin, quantified microfiber release from synthetic fabrics under standard washing conditions. Polyester-cotton blends released close to 138,000 fibers per kilogram of fabric per wash. Acrylic released more. Pure polyester released consistently across all wash conditions tested. No wash temperature, spin speed, or detergent type eliminated shedding. It was reduced by variables but not stopped.
A single garment, washed once a week for a year, releases millions of microfibers into the water system. Scaled across the global activewear market, the volume of synthetic microfibers entering waterways from this category alone is substantial.
Where the Fibers Go
Microfibers released during washing travel through wastewater systems. Treatment plants capture a significant fraction, but the sludge containing captured fibers is often spread on agricultural land, creating a secondary pathway back into soil and groundwater. Research published in Nature Reviews Earth and Environment (Horton, A.A., et al., 2022) documented microplastic contamination across freshwater, marine, and terrestrial environments, with textile microfibers as a primary contributor.
Fibers released during wear follow a more direct route. They shed onto skin, into the air of whatever space the workout occurs in, and onto surrounding surfaces. Indoor environments consistently show higher microfiber concentrations than outdoor ones, partly because synthetic clothing sheds continuously in enclosed spaces. Gyms, studios, and home workout spaces are enclosed environments where multiple people in synthetic activewear are shedding simultaneously.
And beyond the environment, the human body burden data is now established. Leslie et al. (2022), in Environment International, detected microplastic particles in human blood samples. Jenner et al. (2022), in Science of the Total Environment, identified microplastic fibers in human lung tissue. The accumulation is systemic, not just environmental.
Why Workout Clothes Are a Higher-Exposure Category
Not all synthetic clothing creates equal exposure. Workout clothes are in a higher-exposure category because of how they are worn. Close body contact maximizes the skin surface area exposed to shed fibers. High-movement activity maximizes the mechanical stress that causes shedding. Sweating during exercise creates a moist surface that may increase the adhesion of shed fibers to skin. And workout clothes are worn repeatedly and washed frequently, meaning both wear-shedding and wash-shedding occur at higher rates than for garments worn less intensively.
What Lower-Shedding Activewear Looks Like
The shedding problem is a property of synthetic polymer fibers. Cellulosic fibers like TENCEL Lyocell do not shed petroleum-derived plastic microfibers. When TENCEL fibers break down from mechanical stress, the fragments are biodegradable cellulosic material, not plastic particles.
Kaplan et al. (2014), in Fibers and Polymers, documented TENCEL's moisture management and thermal comfort advantages in active wear settings. The performance case for TENCEL does not require accepting higher microplastic exposure as an unavoidable trade-off. The Sempre Leggings are 92% TENCEL Lyocell and 8% spandex. The spandex component does shed synthetic fibers. That is disclosed because partial transparency is not the standard here. The primary fiber is not a plastic polymer, and the shedding profile is categorically different from a garment that is 87% polyester.
The Honest Picture
Workout clothes made from synthetic fibers release microplastics. The research on this is fifteen years deep and consistently pointed in the same direction. Where those microplastics go, including into human blood and lung tissue, is no longer speculative. What remains under active investigation is the specific health effects at accumulating concentrations. What is not under investigation is whether the shedding occurs. It does.
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).
Horton, A.A., et al. (2022). Microplastics in freshwater and terrestrial environments. Nature Reviews Earth and Environment.
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.
Kaplan, S., et al. (2014). Thermal comfort of lyocell and other fibers in active wear. Fibers and Polymers, 15(6).
