You've probably heard the word microplastics. It's been appearing in headlines for a few years now, and the science behind it has been moving fast. But for most people, it still feels abstract - something happening out there, in the ocean, to fish.
The reality is considerably closer to home. And if you're active and train regularly, it's worth understanding exactly what the research is telling us.
What are microplastics?
Microplastics are plastic particles smaller than five millimetres. They enter the environment through the breakdown of larger plastic products - packaging, bottles, industrial waste - and through the direct shedding of synthetic fibres during use and washing. Nanoplastics are smaller still, measuring less than a micrometre, small enough to penetrate individual cells.
They don't biodegrade. They accumulate. And they're now found virtually everywhere - in the deepest ocean trenches, in Arctic ice, in the air we breathe, and increasingly, in the human body.
What the science is finding
The research has moved quickly in the past two years, and what it's revealing is significant.
A 2024 study published in the New England Journal of Medicine found microplastics in nearly 60% of patients' carotid arteries. Those patients had a 4.5 times higher risk of heart attack, stroke, and death over the following three years compared to those without microplastics in their arterial tissue.
A study published in Nature Medicine in early 2025 found microplastic concentrations in human brain tissue at levels seven to thirty times higher than in the liver and kidneys. Brain samples collected in 2024 contained roughly 50% more plastic than equivalent samples from 2016. The same study found higher concentrations in the brains of people who had died with dementia compared to those without.
Microplastics have now been detected in human blood, lung tissue, breast milk, the placenta, the testes, and the liver. In tonsil tissue removed from healthy children, researchers at Stanford found microplastics not just on the surface, but deep within the tissue itself.
The science is still developing. Causation is not always established where correlation has been observed. But the trajectory of the research is clear, and the pace of accumulation in human tissue is accelerating.
Why athletes face a specific problem
Here's the part that doesn't get talked about enough.
If you exercise regularly in synthetic sportswear - and almost all sportswear is synthetic - you are exposing yourself to microplastics more directly than almost any other daily activity.
Synthetic fabrics shed microplastic fibres constantly. Not just in the wash - during wear. Every time you move, stretch, and sweat in polyester or nylon, friction releases microfibres from the fabric. In a gym environment, those fibres become airborne. You're breathing harder than usual. The room is full of other people in synthetic kit doing the same thing. The concentration of airborne synthetic microfibres in that space is significant - and they're going straight into your lungs with every breath.
Then there's what's happening at skin level. During exercise your body temperature rises, you sweat, and your pores open. Research has shown that nanoplastics - the smallest plastic particles, small enough to penetrate individual cells - can be absorbed directly through the skin, with sweat and heat accelerating that process. The garment sitting against your body during a workout isn't just shedding fibres into the air. It's in direct, prolonged contact with open pores.
This isn't a distant, abstract risk. It's happening in the room you train in, with the clothes on your body, every session. The washing machine is a problem too - but the more immediate exposure is the one you're least likely to think about: the kit you're wearing right now.
The sportswear industry's response
The dominant response from the activewear industry has been to switch from virgin synthetic fibres to recycled ones. Recycled polyester, recycled nylon, recycled elastane. The narrative is compelling: plastic bottles diverted from landfill, turned into the leggings you wear to the gym.
But as we wrote in The Problem with Recycled Polyester, recycled plastic is still plastic. And the evidence now suggests it may actually be worse. A December 2025 study commissioned by the Changing Markets Foundation, testing garments from Adidas, HM, Nike, Shein, and Zara, found that recycled polyester sheds 55% more microplastic particles during washing than virgin polyester. The particles were also nearly 20% smaller - meaning they travel further, linger longer, and penetrate more deeply into living systems.
The recycling process weakens polymer chains, making the resulting fibre more brittle and more likely to break apart. The industry's flagship sustainable solution is, by the measure that matters most, making the microplastic problem worse.
The question worth asking isn't which kind of synthetic fibre to use. It's whether to use synthetic fibres at all.
A different answer
Underscored was built on a single design constraint: no petroleum-derived fibres. Ever. Not virgin, not recycled. The fibre itself needs to change, and our job is to prove that performance sportswear can be built without it.
For our first range - the women's Ashdown T-Shirt and Tank and the men's Holmwood T-Shirt - we use TENCEL™ Lyocell, derived from sustainably sourced wood pulp, moisture-wicking, naturally thermoregulating, and fully biodegradable. Alongside it, SeaCell, a bio-based fibre incorporating seaweed, naturally skin-kind and traceable from source. Neither contains plastic. Neither sheds synthetic microfibres. Both perform on court.
As we develop new ranges, the specific fibres will evolve, but the constraint never will. Every Underscored garment, now and in the future, will be built without petroleum-derived fibres.
The Ashdown and Holmwood ranges shed nothing but natural fibres when washed. Natural fibres that biodegrade. That don't accumulate in waterways. That don't end up in the food chain, or in your body.
Performance without compromise. That's what we're here for.
Ready to train without the plastic? Explore our launch ranges - 100% plastic-free, 100% petroleum-free, built for the court.