do your workout clothes shed microplastics?

Polyester, nylon, and elastane are petroleum-derived plastics, spun into thread.

The vast majority of performance running gear is some blend of them. They’re cheap, stretchy, and quick to dry — which is why the industry runs on them. But “technical fabric” is a polite name for woven plastic, and plastic breaks apart into smaller and smaller pieces over its life.

A single wash of synthetic clothing can release up to 700,000 microplastic fibres into the water system. And washing isn’t the only release point — a similar order of magnitude sheds straight into the air around you during ordinary wear, as fabric flexes and abrades against itself and your skin.

These particles don’t just go “away.” Microplastics have now been detected in human blood, lungs, the placenta, and breast milk. The research into what they do once they’re inside us is still young — which is exactly why avoiding an obvious, daily source is a reasonable thing to do rather than wait for certainty.

Running stacks every condition that increases shedding and exposure.

Friction, heat, and sweat together do two things. They accelerate how fast fabric abrades and sheds fibres — and they make your skin more permeable to anything the fabric carries. A 2025 study modelled sweat increasing dermal absorption of PFAS from textiles by up to 3,252× versus dry contact, with the highest concentrations found in sportswear. A garment you sweat hard in, for an hour, with constant friction, is the worst-case version of a plastic you wear.

The reliable fix is to take the plastic out — choose natural fibres rather than relying on washing tricks (guppy bags and filters help with the wash, but do nothing for what sheds into the air as you run). When you shop:

Read the full composition, not the marketing. “Merino” on the front often means a few percent of merino in a mostly-polyester blend, or a merino liner inside a synthetic short — still plastic. Look for 100% natural fibre, and for OEKO-TEX Standard 100 testing, which screens the finished cloth for PFAS and other harmful substances. Of the natural fibres, merino is the one that actually performs for running — it wicks, regulates temperature, and resists odour, where cotton just soaks and sags. We compare them directly in merino vs synthetic running shorts.

Every figure on this page is drawn from peer-reviewed studies, with sources — and the limits of what we claim — on our research page.