Endocrine Disruptors in Clothing: What Polyester Really Is and Why I Stopped Sleeping In It

The Receipts

MoonThreads

Organic Luxury Sleepwear

What polyester actually is, how these chemicals actually work on your hormones, what the human research says, and where I draw the line between evidence and my own opinion.

Polyester is plastic. Plastic starts as crude oil. I want to begin there, because everything else in this article follows from that one sentence.

I spent ten years as a respiratory therapist working in the ICU. That job taught me to ask what something is made of before it goes on or inside of my body. Then I came home one night, opened my own drawer, and realized I had no idea what was in the pajamas I had been sleeping in for years. I had read the ingredient list on my face moisturizer, on the food I consumed, and the water I drank. I never once read the tag on the thing that touched my entire body for eight hours a night.

So I went and read the research. Not the Instagram version. The actual studies, including the ones that disagree with me. Here is what is documented, here is the part that is my opinion, and I am going to be clear about which is which.

What polyester actually is

Conventional polyester is polyethylene terephthalate. PET. It is built from petroleum feedstocks, and it is the same family of plastic as a single use water bottle.

So when a tag says 95 percent polyester, what it is telling you is that almost all of that garment is a petroleum product, spun into thread, and laid against your skin.

What an endocrine disruptor is, in plain words

Your body runs on hormones, and hormones are messages. Estrogen. Testosterone. Thyroid. Insulin. Each message has a receptor it fits into, like a key into a lock.

An endocrine disruptor is a manufactured chemical shaped close enough to one of those keys that the lock answers it anyway.

That is the whole thing. It is a shape problem. And the reason it matters so much is that hormones work at tiny concentrations. Your body is not built to sort real messages from convincing forgeries. It just reads the shape and acts.

How the forged key actually works

It is the part that made me change what I sleep in.

BPA forges the estrogen signal. BPA binds to your estrogen receptors. Your body opens the door and reads it as estrogen, because structurally it is close enough to pass. Researchers do not call it an estrogen imitator as a figure of speech. It is classified as a xenoestrogen, which literally means foreign estrogen, and its activity at the estrogen receptor is one of the most studied mechanisms in the field.

Phthalates jam the testosterone signal. They work from the other direction. The problem phthalates are anti-androgenic, which means they suppress and interfere with testosterone rather than imitate estrogen.

So one group counterfeits the message and the other group blocks it. Both ways, your endocrine system ends up acting on information that did not come from you.

Phthalate syndrome, and why it has a name

Toxicologists have a name for what the problem phthalates do to male reproductive development. They call it phthalate syndrome, and the term appears in a National Academies report.

In animal studies, exposure in the womb during a specific developmental window produces a cluster of effects together: shortened anogenital distance, undescended testes, hypospadias, lowered sperm count, and reproductive tract malformations. The phthalates that cause it are the ones with side chains of roughly four to ten carbons. DEHP. DBP. BBzP. Not every phthalate does this, which matters, and it is worth saying that the clearest version of this evidence is in rats.

But it does not stop at rats, and this is the part I did not know until I went looking.

A 2018 systematic review in Environment International graded the human epidemiological evidence, phthalate by phthalate, using a formal strength of evidence framework. Their findings:

Dose response means more exposure, more effect. That is one of the things scientists look for before they are willing to talk about cause rather than coincidence.

I did not pick the word robust. They did.

Where endocrine disruptors hide in clothing

Here is the practical piece. Plasticizers make plastic soft, so they live wherever soft plastic lives in a garment. Often that is the add-ons rather than the thread itself:

• Coatings and waterproof or water resistant finishes
• Printed graphics, the soft rubbery raised kind, which is called plastisol
• Faux leather, vinyl, rubber trim and elastic banding
• Plastic buttons, sequins, glitter and appliques
• Anything PVC

And PFAS belong in this conversation too. They are the chemistry behind stain resistant, water repellent and wrinkle free finishes, several are endocrine active, and they are called forever chemicals because they do not break down in your body or anywhere else. I wrote about those separately, including which states finally banned them in clothing.

A 2024 review in Environment International pulled together years of lab testing on real garments. In the plastisol used to print graphics onto fabric, plasticizers can be 30 to 60 percent of the total mix. Not a trace. A third to more than half. What testing found in finished products:

Read that last line again. The clean category still ran up to 690.

BPA showed up in clothes people wear every single day

In 2022 and 2023 the Center for Environmental Health tested athletic clothing sold in the United States. They reported BPA at levels that could expose the person wearing it to up to 40 times the limit California sets, and then they filed legal notices.

The brands named across sports bras, shirts, leggings and shorts included Nike, Adidas, Patagonia, Athleta, Alo Yoga, Under Armour, Fabletics, New Balance, Reebok, The North Face, Champion, Skechers, Beyond Yoga, Free People, Outdoor Voices, Asics and Amazon Essentials.

Those are not obscure companies. Those are the brands in my own closet, and in yours. The common thread in what the BPA was found in was polyester blended with spandex.

Sweat, heat, and eight hours: why sleepwear is different

This is the part I care about most, and it is the part the fact checkers usually leave alone, because it is not controversial. It is standard toxicology.

Skin absorption is not a fixed number. It goes up or down depending on conditions. Three of them matter here:

• Wet skin absorbs more than dry skin. Hydration swells the outer layer and makes it more permeable.
• Warm skin absorbs more than cool skin. Higher skin temperature increases permeation.
• Covered skin absorbs more than bare skin. Occlusion, meaning something held against the skin, traps moisture and heat and raises uptake.

This is not a fringe theory. It is the exact principle behind every medicated patch ever made. A nicotine patch is a small piece of material pressed against warm skin, and it delivers a drug into your bloodstream. That is the delivery system working as designed.

Now describe sleeping in synthetic pajamas. Warm skin. Trapped moisture, because plastic does not breathe the way silk and cotton do. Fabric pressed against you and moving on you. Eight hours. Every night.

Those are not neutral conditions. Those are the conditions that maximize absorption, not the ones that minimize it.

And skin absorption is real, not theoretical. In wipe studies, people's hands carried up to 12,900 micrograms per square meter of one phthalate after contact with textiles containing it. In one human experiment, researchers put six men in a chamber with phthalates in the air for six hours, sometimes with a hood so they breathed clean air and only their skin was exposed, then collected every drop of urine for 54 hours. Their skin took in about as much as their lungs would have. For one of the two chemicals, skin alone was essentially equal to breathing it.

Your skin is not a raincoat. It is a door.

What I believe, and what I will not tell you

Everything above this line is documented and I gave you the sources. What follows is my opinion. I am labeling it as mine so you can weigh it as mine.

I believe we are going to look back on wearing plastic against our skin the way we look back on smoking on airplanes. Here is why I hold that.

1. Polyester is a petroleum plastic, and plastics carry chemical additives. That is not in dispute.
2. Several of those additives are known endocrine disruptors with established mechanisms. Also not in dispute.
3. When somebody actually tested ordinary clothing, they found those chemicals in it, in mainstream brands.
4. Skin absorbs them, and absorbs more of them when skin is warm, damp and covered.
5. Microplastics have now been found in human lungs, blood, placenta and testicles in peer reviewed studies. Polyester is plastic and it sheds.
6. In twenty years of this research, the findings have moved in one direction and never once reversed.
7. And you are not only wearing it, you are breathing it. When researchers put a breathing manikin inside real apartments for 24 hours, polyester was 81 percent of all the synthetic plastic in the indoor air. When other researchers examined lung tissue from living people, they found polyester in it, deeper in the lung than they expected it to reach. A bedroom is a closed box, and you are in it for eight hours with fabric moving against your skin all night.

That is seven things I can point at. I think a reasonable person can look at those seven things and decide not to wait.

Here is what I will not tell you. I am not going to tell you your pajamas are making you infertile. Nobody can say that yet, and I am not willing to sell you something on a fear I cannot support. The human research is about total exposure across a whole life, from food packaging and personal care products and dust and air, and no study has isolated one nightgown out of that.

What I am saying is narrower and I think it is harder to argue with. You do not need certainty about one garment to make a reasonable decision about the one garment that touches you for a third of your life. That is the piece of your exposure you can actually control tonight, for free, by changing what you sleep in.

If you are reading this in a cheap synthetic top because that is what you could afford, I am not talking about you and I am not judging you. I wore polyester for thirty years. Nobody told me. That is the whole reason I write these.

How to check your own closet

Five seconds a tag.

1. Read the first fiber listed. Tags list materials by percentage, so the first one is most of what you are wearing. Here is the full tag guide.
2. Feel the graphic. If a printed design is soft, rubbery and slightly raised, that is plastisol, and that is where plasticizers concentrate.
3. Hunt for finish words. Waterproof. Water resistant. Stain resistant. Wrinkle free. Moisture wicking. Antimicrobial. Every one of those is a chemical finish somebody added on purpose.
4. Look at the trim. Faux leather, vinyl, rubber elastic, glitter, sequins, heavy plastic hardware.
5. Look for a real certification. OEKO-TEX Standard 100 tests finished fabric against limits for regulated phthalates, along with hundreds of other substances. It is not a promise about everything in the world. It is a tested floor, which is more than a tag usually gives you.

You do not have to throw anything out today. Start with what touches you the longest. Sleepwear, underwear, the things you are in for eight hours.

What we make

MoonThreads is 100 percent mulberry silk and organic cotton. OEKO-TEX tested. No polyester, no plastisol prints, no toxic azo dyes. I know both of my manufacturers by name and I can tell you which one made which piece.

And here is the simplest version of my whole argument. Plasticizers exist because plastic is stiff and somebody needs it soft. Silk and cotton are already soft. They do not need anything added to feel good against you. So when you pick a fiber that is soft on its own, you are not managing this problem. You are skipping it.

“ Plasticizers exist to make stiff things soft. Silk was never stiff. ”

Sources

Phthalate exposure and male reproductive outcomes: A systematic review of the human epidemiological evidence. Environment International, 2018. sciencedirect.com

Phthalates and Male Reproductive-Tract Development. National Academies of Sciences, Engineering, and Medicine. nationalacademies.org

Phthalate esters in clothing: A review. Environment International, 2024. sciencedirect.com

Transdermal Uptake of Diethyl Phthalate and Di(n-butyl) Phthalate Directly from Air: Experimental Verification. Environmental Health Perspectives, 2015. ehp.niehs.nih.gov

Decrease in Anogenital Distance among Male Infants with Prenatal Phthalate Exposure. Environmental Health Perspectives, 2005. pubmed.ncbi.nlm.nih.gov

New Testing Shows High Levels of BPA in Sports Bras and Athletic Shirts. Center for Environmental Health. ceh.org

Percutaneous Absorption. National Academies Press, via NCBI Bookshelf. ncbi.nlm.nih.gov

Simulating human exposure to indoor airborne microplastics using a Breathing Thermal Manikin. Scientific Reports, 2019. nature.com

Detection of microplastics in human lung tissue using µFTIR spectroscopy. Science of the Total Environment, 2022. sciencedirect.com

Mechanisms of bisphenol A and its analogs as endocrine disruptors via nuclear receptors and related signaling pathways. Archives of Toxicology. link.springer.com

Educational. Not medical advice. The sections marked as my opinion are my opinion.

Keep going: the 8 point sleepwear audit, how to read a clothing tag, and every clean brand I actually buy.

Our tag reads 100% mulberry silk, OEKO-TEX certified. See the nightgown