The Hidden Chemicals in Your Activewear: A Label-Reading Guide
You read the label on your food. You probably read the label on your skincare. But the shirt you sweat in for an hour a day, that sits against your skin while your pores are open and your body is warm? Most of us have never looked closely at what it's made of, or what's been done to it.
Activewear is one of the most chemically processed categories of clothing you can buy. The fabrics are largely synthetic, and synthetics are routinely treated to make them palatable: resisting odor, wicking moisture, shedding water, staying wrinkle-free. (Most of which, incidentally, natural fibers like wool do inherently.) Those treatments are rarely disclosed in plain language on the tag. This guide walks through the most common ones, what your label does and doesn't tell you, and how to actually evaluate what you're putting on.
Why your gym clothes get treated in the first place
Most performance activewear is made from polyester, nylon, or a blend of the two. These are petroleum-based plastics. They're cheap, durable, and stretchy, but on their own they have two problems for athletic wear: they trap odor, and they don't manage moisture or temperature the way natural fibers do. The industry's answer isn't to change the fiber. It's to treat it.
So a polyester shirt becomes "anti-odor" because an antimicrobial agent was added. It becomes "water-repellent" because a chemical finish was applied. It stays smooth because a wrinkle-resistant treatment was baked in. The performance you're paying for is often a coating, not the cloth. And coatings wash out, react with your skin, and end up in wastewater.
The three treatments worth knowing about
Antimicrobial finishes (often silver-based). To keep synthetic fabric from smelling, manufacturers commonly add antimicrobial agents. They work by killing the odor-causing bacteria that thrive on synthetic fibers. The catch is that these finishes can leach out during washing, releasing nanoparticles into waterways where their environmental impact is still being studied, and their long-term effects on skin and the body's own microbiome are not fully settled science.
PFAS-based water repellents. That "water-resistant" or "DWR" (durable water repellent) finish on a lot of performance and outdoor wear has historically relied on PFAS, a class of synthetic compounds nicknamed "forever chemicals" because they don't break down in the environment or the body. PFAS have drawn significant regulatory scrutiny, and several U.S. states have begun restricting or banning them in apparel. The industry is moving away from them, but plenty of treated garments are still on shelves and in closets. Again, the tag rarely names them.
Formaldehyde-based wrinkle resistance. "Wrinkle-free," "no-iron," and "easy-care" finishes have long been produced using formaldehyde-releasing resins. Formaldehyde is a known irritant and a recognized carcinogen at sufficient exposure levels, and it's a common cause of textile contact dermatitis. Amounts in finished garments are typically low and regulated in many markets, but "low" and "harmless" are not the same thing.
None of this means every piece of synthetic activewear is dangerous. It means the things that make synthetic fabric perform are added chemistry, and the label is not designed to tell you which ones, how much, or whether they wash out onto your skin.
What your label actually tells you (and what it hides)
By law in most markets, a garment tag has to disclose fiber content and care instructions. That's it. Fiber content tells you what the fabric is (e.g. 88% polyester, 12% elastane) but it says nothing about what's been applied to it. Care instructions hint at treatments sometimes ("do not use fabric softener," "wash before wearing") but they're written for garment longevity, not for enhancing your knowledge as a consumer.
Here's what a label does not have to tell you: which finishes were applied, what chemicals those finishes contain, whether they're designed to wear off, or whether any residual processing chemicals remain in the fabric you're about to wear. The absence of a warning is not evidence of absence. It usually just means disclosure wasn't required.
This is exactly why third-party certification exists, and why it's the single most useful thing to look for on a label.
How to read a label like someone who knows
A few habits make you a sharper buyer in about thirty seconds:
- Read the fiber content first. The higher the synthetic percentage, the more likely the garment relies on chemical treatments to perform. A natural fiber doesn't need an added antimicrobial to resist odor.
- Treat unexplained performance claims as questions, not features. "Odor-resistant," "water-repellent," and "wrinkle-free" on a synthetic garment usually describe an applied finish. Ask what's doing the work.
- Look for a certification, not an adjective. "Non-toxic" and "clean" are unregulated marketing words. A certification mark is a verifiable, tested standard.
- Recognize the meaningful marks. OEKO-TEX Standard 100 is the one to know: it certifies that the finished textile has been tested against a long list of harmful and regulated substances and falls below defined limits. These are audited standards, not slogans.
Why we don't say "chemical-free" — and what we say instead
Here's the honest part, and it's the part that matters most. At Aiua, we make activewear from 100% merino wool, with no polyester, no nylon, and no blends. Merino does naturally what synthetics need chemistry to fake: it resists odor, manages moisture, and regulates temperature because of how the fiber is built, not because of a finish sprayed on top.
But we are not going to tell you our clothing is "chemical-free," because that wouldn't be true. To make merino fully machine-washable, we use a process known as Superwash, which is applied to the wool to reduce shrinking. Importantly, Superwash has been shown not to shed microplastics, and even biodegrades more quickly than non-treated wool. So we feel comfortable that Superwash is within our high standards of caring for environmental and bodily health. Our wool retains merino's inherent properties, and the machine-washability makes it accessible to more people. That's a win in our book.
Our fabric is certified to OEKO-TEX Standard 100, meaning it's been tested against that standard's list of harmful substances and meets its limits. Our wool is certified to the Responsible Wool Standard, and our supply chain operates under BSCI social compliance auditing, because we believe anything worth doing should be done well.
More informed consumers is always a good thing. In today's day and age there are seemingly limitless choices, each sounding better than the last. The truth is that every choice has its benefits and downsides, and you should go into a purchase knowing you've made the right decision for you. You shouldn't have to trust a brand's adjectives. You should be able to point at a fiber you understand and a certification you can look up. That way you can be confident knowing what's actually touching your skin.
If you'd rather not decode finishes, the simplest move is to start with a fiber that doesn't need them. [Explore our best-sellers] 100% merino wool, OEKO-TEX and RWS certified, nothing hidden on the label.