Fabric Science · Fashion Wellness

Do Synthetic Fabrics Affect Your Hormones? (And What to Wear Instead)

The hormone concern with synthetic clothing is the chemicals riding on the fabric, and your own sweat helps them move. What the science says, and the simple swaps that matter most.

October 21, 2026 · 6 min read

Two friends dancing in a sunlit room in their underwear and loungewear, hair flying, one in a gray bralette set and the other in a nude bra and black silk shorts.

You have probably seen the post. A woman holds up a pair of leggings, says the word polyester like it's a curse, and tells you your clothes are wrecking your hormones. It goes viral. Then you search it, and half the internet says it's true and the other half says it's fear-mongering.

The studies tell a more specific story. In lab tests, polyester's building blocks showed no hormone activity. Some of the chemicals added to it do, and they matter most in one place: the stretchy, sweaty, skin-tight layer you wear closest to your body every day.

What "hormone disruptor" means

Your hormones are messengers. They tell your body when to sleep, when to ovulate, how to handle stress. The National Institute of Environmental Health Sciences defines an endocrine disruptor as a chemical that copies, blocks, or scrambles those messages. Think of a fake key that fits the lock well enough to turn it.

Polyester, on its own, does not seem to be that key. A review of its basic building blocks, summarized by the Food Packaging Forum, found no estrogen-like or testosterone-like activity. So when someone says "polyester is an endocrine disruptor," they skip the step that matters: everything added to it afterward.

The science: what rides on synthetic fabric

Synthetic fabric is plastic spun into thread, and like most plastics, it carries additives. Three families show up again and again in testing, and the NIEHS lists all three among known hormone disruptors.

Bisphenols. BPA is the famous one, the chemical pulled from baby bottles because it can mimic estrogen. BPS and BPF are its close chemical cousins and common replacements. In 2023 the European Food Safety Authority cut its safe daily limit for BPA by about 20,000 times, after newer studies found effects at much lower doses.

Phthalates. These are plasticizers, the chemicals that make plastic soft and bendy. They turn up in printed graphics, coatings, and some synthetic finishes.

Flame retardants and PFAS. Some synthetics carry flame retardants (chemicals that slow burning) or PFAS, the "forever chemicals" used for water and stain resistance. We broke down PFAS in leggings here.

In 2024, researchers in the Czech Republic tested 54 everyday T-shirts and socks and found BPA in 96% of them. The more cotton a garment had, the less BPA it carried. Then they did the math for wearing them. Dry, the clothes stayed under Europe's safe line. Wet, every sample went over it, in what the researchers called an extreme-case estimate. In that worst case, one recycled T-shirt went over by 125 to 570 times.

That same year, consumer groups in four European countries sent 166 underwear products to the lab. Nearly a third (30%) contained bisphenols, and one in ten carried levels well above what's considered safe. Women's underwear fared worst, because most women's lingerie is synthetic. Their finding on fiber was blunt: underwear high in cotton was unlikely to contain bisphenols. They also traced some of it to the dye fixatives used on spandex. (A nonprofit ran this testing, and it has not been peer reviewed.)

It isn't new, either. A 2019 study in Environment International found BPA in 9 out of 10 baby socks sold in Spain, and the sock extracts behaved like hormones in lab tests.

Sweat is the multiplier

Scientists at the University of Birmingham showed in 2023 that the oil in sweat pulls flame retardants out of tiny plastic particles, the way oil lifts a stain. In a follow-up study, they put those particles on lab-grown human skin. Up to 8% of the chemical crossed the skin in a day. Sweatier skin absorbed more.

These were lab models, not people at the gym, and the researchers say so. The research is early, but the studies line up: tests find these chemicals in clothes, lab skin can absorb at least some of them, and sweat pulls more out.

That makes where you wear synthetics, and for how long, the useful question.

What to wear instead

Keep your closet. Rethink the few pieces that sit against your skin the longest, under the most heat. Start here, in this order.

Underwear and bras. The longest contact, the warmest spot, the most synthetic category in a woman's drawer. Swap to organic cotton or silk first. If you want stretch, look for a low elastane (spandex) percentage, or waistbands made with natural rubber. Our edit of non-toxic underwear brands is a good place to start.

Workout clothes. Heat, sweat, and skin-tight fabric are the conditions the lab studies point to. Merino wool handles sweat better than you'd expect and resists odor. Organic cotton works for lower-intensity days.

What you sleep in. You spend eight hours a night in it, under a blanket. Sleepwear in silk, linen, or organic cotton is an easy swap. Start with our 7 best organic cotton pajamas.

Then a few habits that cost nothing:

  • Read the tag. Higher natural-fiber percentages mean fewer plastic layers. Our polyester vs. cotton breakdown explains why.
  • Be skeptical of "natural" synthetics. Bamboo and viscose (rayon) start as plants but go through heavy chemical processing. Check our bamboo and rayon guides before you assume.
  • Look for a real seal. OEKO-TEX Standard 100 tests the finished garment against a long list of harmful substances. GOTS (the Global Organic Textile Standard) covers organic fibers and how they're dyed. Our certification guide sorts the real ones from the decorative ones.
  • Wash before you wear. Researchers who found antimony, a metal used to make polyester, leaching into artificial sweat recommend it.
  • Watch the shiny promises. "Quick-dry," "stain-resistant," "anti-odor." A fabric that does something magic usually had something added to do it.

The bigger picture

The layer against your skin stays there for years, through workouts, warm nights, and long days in leggings. US law requires no chemical disclosure on clothing, so the choice falls to you.

That is the quiet idea behind Fashion Wellness: the clothes you wear are a health choice, the same way food is. You don't have to change everything this weekend. Start with the drawer closest to your body. Swap one thing, then the next. A year from now, the layer touching you most will be the one you trust most.

Sources

Frequently asked

In lab tests, polyester's building blocks showed no hormone activity. The concern is the additives used on it, such as bisphenols and phthalates, which can copy estrogen or interfere with other hormones. Tests keep finding them in synthetic clothing, and sweat raises how much reaches the skin.

No, not on its own. But polyester garments often carry endocrine disruptors. In one 2024 study, garments with more cotton carried less BPA.

Not really. In underwear testing, synthetic fibers as a group carried more bisphenols, and nylon and polyester are both synthetic. Cotton, silk, linen, and wool are the safer bets.

Natural fibers with simple finishing: organic cotton, linen, hemp, silk, and 100% wool. Natural does not guarantee clean, since dyes and finishes still matter, so pair the fiber with a certification when you can.

Not necessarily. In the 2024 Czech study, recycled textiles had almost twice the median BPA of new ones, though the gap was not statistically significant. Recycled polyester is still plastic against your skin.

No study shows that wearing polyester causes infertility in people. The claim traces back to small experiments from the 1990s, including one where 12 dogs wore polyester underwear for two years. Their sperm counts fell, and 10 of the 12 returned to normal after the underwear came off. We found no large human study of everyday polyester underwear. Researchers are separately studying BPA and fertility, with the strongest evidence in animals and less consistent evidence in people, and those reviews look at BPA exposure overall, not clothing. If you're trying to conceive, your doctor is the right person to ask.

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