If you train in modern athletic wear, you're almost certainly wearing plastic. The vast majority of performance fabric on the market is polyester, nylon, or a polyester blend — all synthetic fibers derived from petroleum, all of which shed microscopic plastic particles into the environment and onto your skin. The body of research on microplastic exposure is growing, and what it shows is concerning enough that an increasing number of athletes are switching to natural-fiber alternatives. This article walks through what the current science says, where the exposure comes from, and what to do about it.
What microplastics are and where they come from
Microplastics are plastic particles smaller than 5 millimeters — and microfibers, the kind shed by synthetic clothing, are typically far smaller, often less than 1 millimeter. They're created when plastic products fragment or shed fibers during use. Synthetic clothing is now believed to be one of the largest single sources of microplastic pollution: a single polyester shirt can shed as many as 700,000 microfibers in one wash cycle, according to research published in Marine Pollution Bulletin. The fibers pass through standard wastewater treatment plants, accumulate in waterways and oceans, and increasingly appear in the food chain.
What the research says about human exposure
Microplastics have now been detected in:
- Human blood — A 2022 study published in Environment International found microplastic particles in 80% of blood samples tested.
- Lung tissue — Researchers at the University of Hull found microplastics deep in lung tissue from living patients in 2022.
- Placental tissue — A 2020 study in Environment International identified microplastic particles in human placentas.
- Breast milk — Italian researchers detected microplastics in breast milk samples in a 2022 study.
The full health effects of long-term microplastic accumulation are still being researched, but early findings suggest associations with inflammatory response, oxidative stress, and disruption of normal cellular function. The precautionary case for reducing exposure is increasingly mainstream.
How workout clothes specifically contribute
Athletic wear is uniquely problematic for two reasons. First, the fabrics are typically 100% synthetic, with no natural fibers to dilute the shedding. Second, the friction conditions during exercise — repeated rubbing, stretching, and sweat saturation — accelerate fiber shedding compared to less active clothing. A polyester running shirt sheds significantly more fibers than a polyester button-down would, simply because of the mechanical stress placed on the fabric. The shedding happens both into the air around you and onto your skin, where the fibers can be inhaled or absorbed.
How to reduce your exposure
The most effective change is at the source: choose performance clothing made from natural fibers. Bamboo viscose, merino wool, organic cotton, lyocell, and hemp all perform comparably to synthetics in most athletic contexts and shed no microplastics. Other practical steps:
- Wash less often, and use a microfiber filter. A washing machine filter like the Cora Ball or Guppyfriend bag captures up to 90% of fibers shed in the wash.
- Air-dry when possible. Dryer heat and tumbling accelerate fiber breakdown.
- Buy fewer, higher-quality shirts. Lower turnover means less manufacturing demand and less waste.
- Read labels. "Recycled polyester" and "rPET" are still polyester — they shed the same way as virgin material.
Frequently asked questions
Are microplastics actually dangerous? The full health effects are still being studied, but microplastics have been detected in human blood, lung, and placental tissue, and early research links exposure to inflammatory response and oxidative stress. The precautionary case for reducing exposure is supported by the current evidence.
Does washing my clothes less help? Yes, somewhat. Most fiber shedding happens during machine washing, so reducing wash frequency reduces shedding. Air-drying also reduces fiber breakdown.
Is recycled polyester better? For the planet, recycled polyester reduces virgin material demand, but the shed fibers are functionally identical to those from virgin polyester. From a microplastic exposure standpoint, recycled and virgin polyester perform the same.
Does sweating in synthetic clothes increase exposure? Likely yes. The mechanical stress of exercise — friction, stretching, sweat saturation — accelerates fiber shedding compared to less active wear, and the close contact between fabric and skin during exercise increases the chance of fiber transfer.
What's the easiest way to reduce my exposure? Switch your most-worn pieces — daily t-shirts, gym shirts, base layers — to natural-fiber alternatives like bamboo viscose. Those are typically 50–70% of your weekly wardrobe and the highest-impact swap.
Make the switch. The Kane Essential Tee, Fundamental Tee, and Long Sleeve are 100% bamboo viscose — polyester-free, microplastic-free, and built for daily training. Use code BAMBOO for 15% off.
Related reading: Bamboo vs polyester t-shirt · Best polyester-free t-shirt for men · Why avoid polyester in athletic wear