Do Synthetic Workout Clothes Affect Your Hormones?

Researchers have now found microplastic particles in human blood, lung tissue, and placenta. Synthetic textiles are one confirmed source of that pollution. What's far less settled is what these particles actually do inside the body over time. Here's what's known, what isn't, and why the fabric against your skin is still worth thinking about.

Do synthetic workout clothes actually shed microplastics?

Yes. Every time you wash or wear something made from polyester, nylon, or acrylic, tiny plastic fibres break off and go somewhere: down the drain, into household dust, onto your skin. A single laundry load of synthetic clothing can release hundreds of thousands of these fibres.

Cotton, hemp, and Tencel lyocell shed fibres too. The difference is what they're made of. Natural fibres shed cellulose, which is plant matter and breaks down. Polyester sheds plastic, which doesn't. That distinction is the whole story.

This isn't a fringe concern. Regulators are already acting on it. France began banning several PFAS chemicals, sometimes called "forever chemicals," in clothing textiles from January 2026, and the EU is restricting related compounds in apparel from October 2026.

What have researchers actually found in the human body?

Quite a lot, and quite recently. A 2024 study from the University of New Mexico Health Sciences Center, published in the journal Toxicological Sciences, tested 62 human placenta samples and found microplastics in every single one, at concentrations ranging from 6.5 to 790 micrograms per gram of tissue. Separate research has turned up microplastic particles in human blood, lung tissue, testes, and even brain matter.

None of that proves the particles came from anyone's gym leggings specifically. Microplastics also come from food packaging, house dust, tap water, and dozens of other everyday sources. But textiles, especially the kind you wash often and wear against sweaty skin, are one of the sources researchers keep coming back to.

Does this mean your leggings are messing with your hormones?

No, and anyone who tells you that with total confidence is overselling the science. What's actually established is narrower. Microplastic particles can carry chemical additives on their surface, things like phthalates and PFAS, and some of those specific chemicals are known endocrine disruptors in other, better-studied contexts, like food packaging and personal care products.

Lab and animal studies link microplastic exposure to oxidative stress, inflammation, and hormone disruption. Human studies on the same question are mostly observational so far, meaning researchers can point to correlations but not yet prove cause and effect. There is also no established safe exposure limit for microplastics in humans, simply because there isn't yet enough data to set one. That's an honest gap in the science, not a hidden conspiracy.

What about wearing synthetic activewear during pregnancy?

This is where a lot of the searching on this topic actually comes from, so it deserves a direct answer. Microplastics have shown up in every placenta sample tested in the research so far. That finding is part of why some people choose to reduce synthetic, plastic-based products during pregnancy as a precaution, the same reasoning behind avoiding certain plastics in food storage.

That's a personal choice, not a medical instruction, and a clothing brand isn't qualified to give you one. If you have specific health questions about your pregnancy, that conversation belongs with your doctor.

How big a piece of this is clothing, really?

A meaningful one, but not the only one. Microplastics also come from food packaging, tap water, dust in your home, and the breakdown of larger plastic waste outdoors. Textiles stand out for two reasons: they're one of the few sources with a proven, measured release mechanism, since researchers can put a garment in a washing machine and count the fibres that come out, and they're one of the few sources you can personally choose to change.

You can't rule out every source of exposure in your life. You can decide what fabric spends several hours a week directly against your skin while you sweat. That's a smaller lever than fixing global water treatment, but it's a real one, and it's entirely within your control.

So what can you actually control?

You can't filter microplastics out of tap water with a workout top. But the fabric against your skin, especially during exercise, when you sweat more and your pores are more open, is one of the few textile decisions that's entirely yours to make.

That's the actual reason Strand works only with organic cotton, hemp, and Tencel™ lyocell. None of them are plastic. None of them shed microplastic fibres in the wash. It isn't a cure for anything, and we'd never claim it was. It's one less synthetic layer against your skin, for however many hours a week you're sweating in it.