September 01, 2026

What Your Sweat Is Really Absorbing: Why We're Falling Back in Love With Natural Fibres

A love letter to your skin, from dea 🌙

Here's a question we don't ask ourselves nearly enough: when you get hot, what is your workout gear doing to you — and what are you doing to the planet?

We tend to think of clothing as a passive layer. Something we put on and forget about, like wallpaper for your body. But the moment you heat up — mid-flow on the mat, three songs into spin class, easing into a sauna — your skin stops being passive too. Pores open. Blood rushes to the surface. And whatever's sitting against you, natural fibre or plastic-based synthetic, starts moving both ways: into you, and out into the world.

That's the conversation we want to have today. Not from a place of fear — think of it more like finally reading the ingredients label on the thing you've been wearing five days a week. Once you clock the two-way exchange happening between your skin and your clothes, going natural stops feeling like a "wellness trend" and starts feeling like, well... obvious.

Heat: your skin's version of leaving the door unlocked

Your skin is your largest organ, and it is not a wall — it's more like a bouncer who gets a lot more relaxed about who it lets in once you're hot and sweaty. That's exactly why nicotine patches and other medicated patches come with warnings to keep them away from heat pads, saunas and hot baths — heat and blood flow are a fast-pass for absorption.

Great news if what's touching your skin is clean. Less great if it's polyester, nylon, or a chemical wrinkle-resistant finish, all queuing up at the door the moment you break a sweat.

Plot twist: it's not just in your washing machine, it's in you

Most of the microplastics conversation focuses on the ocean — and yes, your washing machine is a real contributor. But here's the part that should really get your attention: microplastics aren't just polluting waterways anymore. They're turning up inside us.

A 2024 study out of the University of New Mexico, published in the journal Toxicological Sciences, tested 62 human placentas...and found microplastics in every single one, with polyethylene — the plastic most commonly used in packaging — the most common culprit.

A separate 2022 study in Environment International found plastic particles in human blood for the first time. Scientists have since found them in lungs, arteries, breastmilk, and even the brain.

And researchers have now found microplastics in human semen and testicular tissue.

Nobody's saying your leggings alone are responsible for that. But every wash, every workout, every hot sweaty gym session where synthetic fibres rub, stretch and shed against your skin is one more small contribution to a body burden scientists are only just starting to measure. As functional medicine physician Dr. Mark Hyman puts it, "polyester and synthetic fibers also are a big issue" — precisely because of what happens every time they're washed and worn.

Natural fibres like organic cotton and merino don't add to that tally. What they shed is cellulose or protein — compostable, not "still here in 200 years and now possibly in your bloodstream."

The chemistry that comes with the plastic

Microplastics are only half the story. Synthetic activewear also carries the chemicals used to make it perform. Water-repellent and stain-resistant finishes are often made with PFAS, the "forever chemicals", and polyester-spandex blends can contain additives like bisphenols.

Sweat matters here. Recent lab research suggests sweat can pull PFAS out of textiles and help them transfer to skin, and other lab work shows some PFAS can cross human skin. Independent testing in the US, carried out by the Center for Environmental Health, found BPA in polyester-spandex sports bras and leggings at up to 40 times California's safe limit. Scientists are still working out how much of this reaches your bloodstream from clothing, but it's one more reason we choose fabric with nothing added to it.

What's in the colour

Where your fabric gets its colour matters too. Polyester can't be dyed with the same dyes as cotton, so it's coloured with disperse dyes, which sit loosely in the fibre. Some of these, including certain azo disperse dyes, are among the best-documented causes of textile contact allergy. DermNet NZ notes that sweat and rubbing make dye leach out more, and that reactions often show up at the waistband and upper thighs. Their advice for sensitive skin is natural fibres like cotton.

Botanical dyes are different at the source. Colour from plants is fixed to the fibre in a bath we control, and every input is something we can name.

Sauna time: swap the togs, save your pores

Quick scenario: you finish your workout, then head straight into the sauna in synthetic swimwear or leggings — the hottest, sweatiest test your clothing will ever face.

Neuroscientist Andrew Huberman has said "deliberate heat exposure can be a powerful tool to improve health and longevity" — and he's right, sauna sessions genuinely support cardiovascular health, recovery, and mood. But the benefit is only as clean as what's sitting on your skin while you get it.

Synthetic swimwear is built to survive chlorine and chemical pools, not to sit against wide-open pores for twenty minutes in dry heat.

Heat and sweat make it easier for finishes and dyes to leave the fabric. Cotton has nothing to leach: no performance coatings, no fluorinated finishes, just fibre. Organic cotton underwear is breathable, biodegradable, and skips the plastic base and dye-fixatives entirely.

The swap: save the togs for the pool, bring GOTS-certified organic cotton undies for the sauna bench. Your skin (and your lungs) will thank you.

Why natural fibres, in short

They breathe — no chemical coatings required, just cotton doing what cotton does
They don't add to your plastic tally — what sheds is compostable, not forever-plastic
They're free of PFAS and fluorinated finishes — nothing added to repel water or stains
They're gentler on sensitive skin — no resin finishes, no formaldehyde by-products and none of the disperse dyes linked to textile allergy
They return to the earth — instead of sitting in landfill for centuries
They keep the whole chain cleaner — GOTS certification and plant-based dyes mean the people making your clothes stay safer too

This isn't about being precious. It's about making sure the fabric touching your skin at your most open-pored, most alive moments is as clean as everything else you're already mindful of.

Healthy activewear low toxins organic cotton bike shorts

A healthier wardrobe doesn't have to be complicated

At dea, we've never believed that living more consciously means living perfectly.

It's about noticing.

Noticing what we eat.
Noticing what we put on our skin.
Noticing where our clothes come from.
And noticing what touches our bodies for hours every day.

We can't control everything we're exposed to in the modern world.

But we can make little choices.

One natural-fibre garment.

One less plastic layer.

One more organic cotton piece.

One thoughtful purchase instead of three impulsive ones.

Because wellness isn't just what happens in the gym.

It's what happens in the little spaces between everything else.

And sometimes, feeling a little better can begin with something as simple as changing what you're wearing.

Choose natural where you can.
Choose organic where you can.
And above all, choose kindly.

That's the dea way.

One step you can take today 🌿

Don't overhaul the whole wardrobe tonight. Just swap the one piece that touches your skin the most, for the longest, while you're hottest and sweatiest: