Microplastics in your activewear: what we actually know about plastic fibers, sweat, and your skin

Most adults spend twelve to sixteen hours a day in direct skin contact with synthetic fiber. Leggings, sports bras, base layers, compression shorts, gym socks, the hoodie pulled on after the workout. The fabric closest to your skin, for the longest portion of your day, is in the vast majority of cases a petroleum-derived plastic blend. Polyester, nylon, elastane, polyurethane coatings, antimicrobial finishes. We have normalized this so completely that the question almost feels strange to ask: what is this stuff doing to the body it is pressed against?

The honest answer is that we are still mapping it. But the picture that has emerged over the last decade of microplastics research is specific enough, and mechanistically clear enough, that it no longer reads as speculation. Activewear is one of the largest unregulated sources of microplastic shedding in the home. The fibers it sheds are small enough to be inhaled and, under certain conditions, small enough to cross biological barriers. And the plastic polymer itself is rarely the most concerning component. The additives are.

This is not a fear piece. The mechanisms are knowable, the alternatives exist, and the regulatory environment is beginning to shift. What follows is what the science actually says, where it is still uncertain, and what to do with that information.

What a microplastic actually is

A microplastic is any plastic particle smaller than 5 millimeters. The category includes everything from visible pellets used in industrial molding down to fragments under one micrometer, which are classified as nanoplastics. The activewear-relevant fraction sits in the fiber range: thin, elongated shards of polymer, typically 10 to 500 micrometers long, shed from the surface of synthetic fabric as it flexes, abrades, and degrades.

These fibers come from the same materials that make up most performance clothing:

• Polyester (PET), the dominant synthetic in athletic apparel
• Nylon (polyamide 6 or 6,6), common in compression and swim
• Elastane / spandex / Lycra (segmented polyurethane), the stretch component in nearly every modern garment
• Acrylic, polypropylene, and polyurethane coatings on water-resistant pieces

Each of these is, chemically, a long-chain hydrocarbon polymer derived from crude oil or natural gas. When intact, the polymer is relatively inert. The issue is that fabric does not stay intact. It sheds.

How activewear sheds during wear, not just washing

The conventional framing of microplastic pollution focuses on the washing machine, and for good reason. A single domestic wash of synthetic garments can release hundreds of thousands to several million fibers into wastewater, depending on fabric construction, agitation, and load size. Wastewater treatment captures some of this. The rest enters waterways.

But the wear-side shedding is the part that matters for your body. Activewear is engineered for movement, friction, sweat, and heat, and every one of those conditions accelerates fiber release.

• Mechanical abrasion. Every step in a run, every squat, every rotation through a sleeve creates fiber-on-fiber and fiber-on-skin friction. Fabrics shed continuously. A 2022 study estimated that wearing synthetic garments releases comparable, sometimes higher, microfiber loads to the air as washing them releases to water.
• Heat. Skin temperature under a compression garment during exercise commonly reaches 35 to 38 degrees Celsius, and the trapped microclimate can run higher. Heat increases polymer chain mobility and accelerates the leaching of additives. It does not melt the fabric. It softens the matrix enough for plasticizers and surface-applied chemicals to migrate more freely.
• Sweat. Sweat is a complex aqueous solution containing salts, urea, lactate, and lipids. It is not pure water. The lipid fraction in particular is relevant, because many of the chemicals of concern in synthetic fabric are lipophilic. They prefer to move into oily phases, including sebum.
• UV and oxidative degradation. Sunlight and oxygen embrittle polymers over the lifetime of a garment. An older legging sheds more than a new one. The fabric you have washed fifty times is not the fabric you bought.

The result is a near-continuous low-level release of fibers and fiber-associated chemicals at the skin surface, in a warm, moist environment optimized for absorption.

The dermal route and the inhalation route

Two exposure pathways matter for clothing: through the skin, and through the air directly around the wearer.

Skin

Skin is the largest organ of the body. Roughly 20 square feet of absorptive surface, densely vascularized, rich in receptors, and far from the passive barrier it is sometimes described as. Lipophilic small molecules cross the stratum corneum routinely. This is why nicotine patches, hormone patches, and topical drugs work.

The question for microplastics is twofold. First, do intact particles cross the skin barrier? Second, do the chemicals associated with those particles cross?

For intact particles, the current evidence suggests that particles above roughly 1 micrometer do not penetrate healthy skin in meaningful amounts. Smaller nanoplastics, particularly below 100 nanometers, are a more open question. In vitro and animal studies have shown some translocation, especially through hair follicles and compromised skin barriers. In humans, this remains an area of active research and should not be overstated.

For the chemicals carried by those particles, the picture is clearer. Plasticizers, surfactants, dyes, and surface-applied finishes are routinely detected on skin after wear, and many are known to be dermally absorbed. The genital and inner-thigh skin, which is thinner and more permeable than skin on the arm or back, sits in direct contact with leggings, compression shorts, and underwear, in proximity to hormone-sensitive reproductive tissues. This is the absorption geometry that most concerns endocrine researchers.

Inhalation

Microfibers shed from clothing accumulate in indoor air. Studies of indoor dust consistently find synthetic textile fibers among the dominant particle types. People wearing synthetic clothing in poorly ventilated rooms inhale measurable quantities of these fibers, and fibers small enough to reach the deep lung have been recovered from human lung tissue in postmortem studies.

The dose is small. The exposure is daily, lifelong, and additive. The framing that matters here is not acute toxicity. It is chronic, cumulative load on a system that did not evolve to clear synthetic polymer fragments.

The chemicals are the story

The polymer alone is not the most concerning part of a synthetic garment. The additives and finishes are. A plastic fiber is rarely just plastic. It is a delivery system for the chemistry layered on top of it.

Four categories matter most for activewear.

PFAS (per- and polyfluoroalkyl substances). Used as water-repellent and stain-resistant finishes, particularly on outerwear, swim, and "sweat-wicking" pieces. PFAS are persistent. They bind to serum proteins, accumulate in the liver and kidneys, and have been linked in epidemiological studies to altered thyroid function, immune effects, lipid metabolism changes, and certain cancers. The defining feature is the carbon-fluorine bond, one of the strongest in organic chemistry, which is why these compounds are sometimes called forever chemicals.

Phthalates. Plasticizers used to soften plastics, including in printed graphics, coatings, and some elastane formulations. Phthalates are not chemically bonded to the polymer. They migrate. Several phthalates, including DEHP, DBP, and BBP, are classified as endocrine disruptors and have been associated with effects on androgen signaling and reproductive development in animal and human studies.

BPA and related bisphenols. Used in some polyester production and as additives in polyurethane coatings and recycled-content yarns. Bisphenols bind weakly to estrogen receptors and have been linked to effects on hormone signaling at low doses, particularly during developmental windows. Recycled polyester, often marketed as the sustainable choice, can carry higher bisphenol loads than virgin material due to contamination during recycling.

Antimicrobial silver and other biocidal finishes. Marketed as odor control in athletic apparel. The mechanism is the release of silver ions, which are broadly toxic to bacteria, and to human cells at higher doses. Silver-treated fabrics shed silver during wear and washing, and the long-term effects of chronic low-dose silver exposure on the skin microbiome are not well characterized. The skin microbiome is not a problem to be solved. It is a regulatory organ in its own right.

Fabric is not neutral. It is part of your biological environment.

The pattern across all four categories is the same. Small molecules, lipophilic or protein-binding, present at low concentrations in a garment, released slowly under heat and sweat, absorbed through skin or inhaled from indoor air, persistent in the body. The issue is not the single exposure. It is the duration.

Why "just wear cotton" does not solve this

The intuitive answer is to switch to natural fibers. The problem is that almost no activewear is actually a natural fiber.

• Cotton activewear is, in nearly every case, a cotton-elastane blend. The stretch is plastic. The "cotton" leggings on the rack are typically 88 to 95 percent cotton, 5 to 12 percent elastane. The elastane is the part doing the shedding and the chemical leaching.
• Bamboo apparel is, with rare exceptions, bamboo viscose, a regenerated cellulose fiber produced by dissolving bamboo pulp in carbon disulfide and sodium hydroxide. The starting material is plant-based. The finished fiber is a chemically processed rayon. Calling it natural is a marketing decision, not a material one.
• Merino wool has excellent thermal and odor properties but limited stretch and recovery. Merino activewear is almost always blended with nylon or elastane to achieve the fit consumers expect.

The result is that the natural-fiber shelf in most athletic stores is, on inspection, a synthetic-blend shelf with natural-fiber branding. Anti-greenwashing here is not a moral position. It is reading the content label.

The bio-based answer

The real fix is not to retreat to imperfect natural fibers. It is to rebuild the high-performance fiber itself from plant-derived feedstock, with the additives stripped out and the chemistry verified.

Bio-based polyamide, produced from agricultural inputs such as castor oil, corn, and straw residue, is chemically a nylon. It performs like a nylon. It also takes carbon out of the petroleum supply chain, can be manufactured without PFAS finishes, antimicrobial silver, or fragrance infusion, and can be paired with a bio-based stretch fiber for four-way recovery. This is the construction we built at Ohzehn: a 99.5 percent plant-derived feedstock, 76 percent bio-based nylon, 24 percent bio-based stretch, third-party tested in U.S. labs for BPA, PFAS, phthalates, heavy metals, formaldehyde, and azo dyes. Performance built into the fiber architecture, not applied as a finish.

The point is not the brand. The point is that the technology exists. The old standard was aesthetic. The new standard is biological compatibility.

What regulators are doing

Regulatory pressure is building, unevenly, but in a clear direction.

• The European Union has adopted restrictions under REACH on intentionally added microplastics, with phased bans through 2028, and is advancing broader microplastic legislation under the Zero Pollution Action Plan. ECHA has also proposed a near-total restriction on PFAS as a class.
• Australia has introduced restrictions on three legacy PFAS compounds (PFOS, PFOA, PFHxS) under the Industrial Chemicals Environmental Management Standard, effective July 2025.
• The United Kingdom is consulting on PFAS restrictions and microplastic standards as part of its post-REACH chemicals framework.
• In the United States, regulation is moving state by state. California, New York, Maine, and Washington have all enacted or scheduled bans on intentionally added PFAS in apparel, with California's ban taking effect January 2025.

The direction of travel is consistent: disclose, restrict, replace. Brands that have not started reformulating will be doing it under deadline.

What an informed consumer or brand can actually do

The practical posture is not panic. It is selection.

• Read content labels. Cotton-elastane is not cotton. Recycled polyester is still polyester, and may carry higher additive loads than virgin.
• Avoid added antimicrobial finishes. Look for "silver-free" or simply the absence of "antimicrobial" claims on activewear.
• Avoid PFAS-treated water repellency on garments worn against skin. If a piece is marketed as water-repellent or stain-resistant, ask the brand directly whether it uses PFAS-based DWR.
• Wash synthetics less, in cooler water, in shorter cycles. Use a microfiber-capture bag or filter on the washing machine.
• Ventilate. Indoor microfiber concentrations drop substantially with regular air exchange.
• When replacing pieces, prioritize fiber transparency over fiber familiarity. A verified bio-based nylon with a clean additive profile is a better outcome for the skin than an undisclosed cotton blend.

For brands, the work is harder and more interesting. It means specifying feedstock, eliminating PFAS and antimicrobial silver, third-party testing for the chemicals that actually matter, and being honest on the label about what the fabric is and is not.

The fabric closest to your skin is not neutral. It is part of your biological environment. The science is far enough along that this is no longer a fringe view. The mechanism is the story, the chemistry is fixable, and biological compatibility is becoming the standard the next generation of performance fabric will be measured against.

Dougie Taylor

Co-Founder, Ohzehn Textiles · Building plastic-free performance apparel