You obsess over what you eat. You track your sleep. You do the breathwork. You watch your recovery. And then you spend four hours a day wrapped in plastic — pressed against your skin, heating up with your body, soaking in your sweat — and wonder why your hormones are off, your skin keeps breaking out, and your inflammation never fully clears.
The rash guard you're training in right now is made from polyester. So is probably everything underneath it. And polyester is not just a fabric. It is a delivery mechanism — for phthalates, BPA, PFAS, antimony, synthetic dyes, formaldehyde, and a cocktail of endocrine-disrupting chemicals that migrate through your skin every time your body temperature rises and your pores open.
This is not a fringe concern. The research is accumulating fast. Microplastics have been found in human blood, semen, lung tissue, and placental tissue. Chemicals common in synthetic athletic wear are directly linked to reduced testosterone, impaired sperm production, and hormonal disruption. And for grapplers — who spend more time in tight, heat-generating synthetic clothing than almost any other population — the exposure is concentrated and chronic.
If you want to stay hard to kill in midlife, you need to know what you are wearing.
What Polyester Actually Is
Polyester is not a natural fibre. It is a synthetic polymer — essentially plastic — derived from petroleum. The manufacturing process involves antimony trioxide as a catalyst, which remains as a residue in the finished fabric. The resulting material is then dyed, treated for moisture wicking, finished for durability, and sometimes coated with PFAS for water resistance.
The result is a garment that looks and feels like clothing but is, chemically, closer to a sheet of treated plastic wrap. And when you put it next to your skin — especially in the groin region, where skin is thinner, more absorptive, and thermally sensitive — and heat it up with exercise, you create optimal conditions for transdermal chemical absorption.
Used as a catalyst in 80–85% of polyester production. Mimics estrogenic activity in the body. Residues remain in finished garments and can migrate through the skin, particularly during sweating. Linked to dermatitis and endocrine disruption.
Used to soften plastics and fix inks and dyes to synthetic fibres. Found above safe thresholds in 20% of fast-fashion synthetic items. Absorbed through skin and inhaled. Directly linked to reduced testosterone production, lower sperm counts, and increased fertility problems in men. The European Chemicals Agency classifies several phthalates as substances of very high concern.
Best known in plastic bottles but also found in textile coatings and spandex-polyester blends. Studies have found BPA at up to 19 times safety limits in some polyester garments. A known endocrine disruptor linked to hormonal imbalance, reproductive system disruption, and increased cancer risk.
Per- and polyfluoroalkyl substances added to activewear for moisture resistance and sweat-wicking properties. Detected in 65% of children's synthetic clothing and found in the blood of people across the globe. Virtually indestructible — they do not break down in the environment or the human body. Linked to cancer, thyroid dysfunction, immune suppression, and fertility disruption. A 2022 study by Toxic-Free Future found 72% of water or stain-resistant products tested positive for PFAS.
Approximately 90% of garments today are coloured with synthetic dyes. Disperse dyes — used heavily in polyester because the fibre resists water-based dyes — are among the worst culprits for skin sensitisation and allergic reaction. Azo dyes, of which there are over 2,000 varieties, can degrade through skin bacteria into aromatic amines — compounds classified as known carcinogens. Germany recognises bladder cancer as an occupational disease for textile workers. There is no specific federal regulation restricting azo dyes in the United States.
Used in wrinkle- and shrink-resistant treatments on synthetic fabrics. A Class 1 carcinogen. Responsible for the "new clothes" smell many people recognise from fresh athletic wear. Associated with respiratory irritation, skin sensitisation, and in higher exposures, increased cancer risk. Commonly found in poly-cotton blends and performance finishes.
Used as stabilisers and pigments in textile dyeing processes. Lead and chromium are commonly found in synthetic clothing dyes. Cadmium is used to create bright pigments in activewear. At elevated concentrations these metals accumulate in the body and are associated with brain, kidney, liver, and reproductive system damage, as well as immune suppression. The EU's REACH Regulation sets legal limits; US federal regulation remains limited.
Polyester Underwear & the Testosterone Crisis
This is the part that should concern every man reading this — particularly those of us in midlife who are already navigating a natural decline in testosterone and doing everything we can to maintain hormonal health, recovery, and performance.
The research on polyester underwear and male reproductive function stretches back further than most people realise. Professor Ahmed Shafik of Cairo University published several landmark studies on this subject across the 1990s. In one study, men wearing polyester underwear daily showed significant decreases in testosterone levels and sperm counts — and in some cases, measurable azoospermia (absence of viable sperm) — that reversed after they switched to cotton. The contraceptive effect was so pronounced that he published research in the journal Contraception exploring it as a method of non-surgical male contraception.
In a separate animal study published in the Journal of Urology (Saxena et al., 1993), dogs wearing polyester underwear for 24 months showed significant decreases in sperm count and motility, increases in abnormal sperm forms, and elevated serum testosterone markers — all of which partially reversed when the garments were removed.
That was the 1990s, before the microplastic and chemical contamination load in synthetic garments was anywhere near what it is today.
Polyester generates a weak but measurable electrostatic field during wear. Shafik's research found this field may directly interfere with spermatogenesis and hormonal signalling in the testes — independent of heat effects.
Research published in Environmental Health Perspectives found that men with higher urinary phthalate metabolite levels had significantly lower testosterone and reduced fertility markers. Phthalates are found in polyester clothing and absorbed transdermally during wear — especially during exercise when sweat drives chemical migration through the skin.
A 2022 study published in PubMed found that polystyrene microplastic exposure in mice reduced testosterone levels by downregulating the LH-mediated LHR/cAMP/PKA/StAR pathway — one of the primary signalling chains controlling testosterone production in the testes. A 2024 multi-site study in China examining semen samples from 113 men found direct associations between mixed microplastic exposure and impaired sperm function.
Exercise elevates body temperature and increases sweat production. A 2023 University of Birmingham study confirmed that sweat-mimicking solution leaches hazardous chemicals — including flame retardants and phthalates — from microplastic fibres. The rate of dermal absorption of certain chemicals can increase by up to 50% during sweating. For grapplers training twice a day in tight polyester rash guards and shorts, this is not an occasional exposure. It is a daily, high-intensity chemical delivery event.
Shafik, A. (1992). Contraceptive efficacy of polyester-induced azoospermia in normal men. Contraception, 45(5), 439–451.
Saxena, P., Prasad, R., & Haldiya, K.R. (1993). Effect of different types of textile fabric on spermatogenesis. Urological Research, 21(5), 367–370.
Zhang, C., Chen, J., Ma, S., Sun, Z., & Wang, Z. (2022). Microplastics may be a significant cause of male infertility. American Journal of Men's Health, 16(3), 1–4.
Kim, M. J. et al. (2022). Chronic exposure to polystyrene microplastics induced male reproductive toxicity via the LH-mediated LHR/cAMP/PKA/StAR pathway. PubMed, PMID 35177090.
Mínguez-Alarcón, L. et al. (2018). Underwear type and semen quality — European Society of Human Reproduction and Embryology study of 656 men.
Zhang, C. et al. (2024). Association of mixed exposure to microplastics with sperm dysfunction: a multi-site study in China. EBioMedicine, 108, 105369.
Microplastics: They Are Already Inside You
This is no longer a hypothetical risk. The question of whether microplastics are entering the human body has been answered. They are — in volume and in locations that should concern every person reading this.
- Human blood — confirmed circulating throughout the cardiovascular system (Jenner et al., 2022, Environment International)
- Human semen — found in every sample tested in a 2024 Chinese study
- Human placental tissue — confirmed in the first evidence study (Ragusa et al., 2021, Environment International)
- Lung tissue — confirmed presence of inhaled synthetic fibres
- Testicular tissue — microplastics and associated chemicals found to cause direct cellular damage
- Infant faeces — higher concentrations than adults, linked to synthetic clothing and product exposure
A single polyester garment releases up to 496,030 microfibers per wash, according to research by Napper & Thompson (2016). A single load of polyester laundry can release over 700,000 microfibers into the water system (Browne et al., 2011, Philosophical Transactions of the Royal Society B). These fibres escape filtration, enter waterways, concentrate in marine life, and return to us through our food supply. Humans ingest an estimated 39,000 to 52,000 microplastic particles annually (Cox et al., 2019) — and those numbers have risen since that study was published.
For grapplers, the exposure pathway is more direct. You are not just washing your rash guard and releasing fibres into the water. You are wearing it against your skin at elevated body temperature, in high sweat conditions, for hours at a time. The fibres shed onto your skin. The chemicals migrate through it. You inhale shed fibres in the training environment. And you do this daily.
The Rash Guard Problem — Skin Infections & the Grappling Microbiome
Beyond the hormonal and reproductive effects, there is a more immediate consequence for grapplers that most people are treating as bad luck or poor hygiene when it is actually a direct result of the fabric they are wearing.
Polyester does not breathe. It does not absorb sweat — it wicks it, which means it keeps moisture moving across the surface of the skin rather than away from it. Polyester traps heat and moisture against the skin, creating bacterial breeding grounds that cause breakouts, rashes, and opportunistic infections. For grapplers — who are already in skin-to-skin contact with training partners and mats that carry their own microbial load — this is a compounding problem.
The chemical profile of your rash guard makes it worse. Sweat can leach chemicals from microplastic fibres into the skin through sweat glands and sebaceous glands, disrupting the skin's natural barrier and microbiome. A disrupted skin microbiome is a skin that cannot defend itself against the bacteria and fungi it encounters daily on the mats.
The Specific Infection Risks
Inflammation of the hair follicles triggered by sweat, heat, and friction in tight synthetic fabrics. Common in areas covered by rash guards and compression shorts. The chemical disruption of the skin microbiome reduces the skin's natural ability to keep this in check.
Dermatophyte fungi thrive in warm, moist, low-oxygen environments. Polyester creates exactly these conditions. The compromised skin barrier from chronic chemical exposure makes colonisation more likely. Grapplers already face elevated fungal exposure from mat contact — synthetic underwear and rash guards make the body a more hospitable host.
Disperse dyes in polyester are considered some of the worst culprits for skin allergies. As dermatologist Dr. Susan Nedorost noted, "regardless of a history of prior dermatitis, anyone can become allergic to dyes in clothing." What presents as a mat-acquired skin reaction is sometimes a reaction to the dyes in your own clothing.
Many synthetic athletic garments are treated with antimicrobial agents — triclosan and silver-based compounds — marketed as odour control. These treatments disrupt the skin microbiome indiscriminately, killing protective bacteria alongside pathogenic ones. The result over time is a skin ecosystem that is less resilient, not more — and more vulnerable to the exact infections grapplers are trying to avoid.
"You spend four hours a day optimising your training and recovery — and then you wrap yourself in plastic and cook in it."
— Josh Button · @thatjiujiteiroThe Chemical Exposure Table — Know What You're Wearing
| Chemical | Where It's Found | Primary Health Risk | Regulation Status (US) |
|---|---|---|---|
| Phthalates | Polyester, spandex, printed designs, synthetic dyes | Reduced testosterone, impaired sperm production, endocrine disruption | Limited — some restricted in children's products only |
| BPA / Bisphenols | Textile coatings, spandex-polyester blends, fabric finishes | Hormonal disruption, reproductive harm, increased cancer risk | Largely unregulated in textiles |
| PFAS | Moisture-wicking, water-resistant, and stain-resistant activewear | Cancer, thyroid disease, immune suppression, fertility disruption | Banned in NY (2023), CA (2025). No federal textile ban. |
| Antimony | All polyester (manufacturing catalyst) | Estrogenic activity, dermatitis, respiratory toxicity | No specific clothing regulation |
| Disperse / Azo Dyes | Brightly coloured synthetic activewear and rash guards | Contact dermatitis, carcinogenic aromatic amines (azo), allergic sensitisation | Some aromatic amines restricted. Azo dyes largely unregulated. |
| Formaldehyde | Wrinkle-resistant and shrink-resistant fabric treatments | Respiratory irritation, skin sensitisation, carcinogen (Class 1) | No specific clothing limit set |
| Heavy Metals (Pb, Cd, Cr) | Synthetic clothing dyes, cheap zippers, pigments | Brain, kidney, liver, reproductive system damage; immune suppression | Limited — some restricted through CPSC in specific products |
| Microplastic Fibres | All polyester, nylon, and spandex garments | Systemic accumulation, inflammation, endocrine disruption, potential carcinogenicity | No regulation |
What to Do About It
You cannot eliminate every exposure. But you can make targeted decisions that meaningfully reduce the chemical load on your body — particularly in the areas of highest skin contact and hormonal sensitivity.
- Switch your underwear first. This is non-negotiable. The groin region has thinner skin, higher vascularity, and thermal sensitivity that makes it the highest-risk zone for transdermal chemical absorption. Switch to 100% organic cotton, bamboo lyocell, or merino wool underwear immediately. This is the single highest-impact change you can make.
- Rash guards — go OEKO-TEX certified. You may not be able to avoid polyester in your rash guard entirely — the performance requirements of grappling are real. But you can choose garments certified by OEKO-TEX Standard 100, which tests for and restricts harmful chemicals including heavy metals, phthalates, formaldehyde, and certain azo dyes.
- Avoid bright colours in rash guards and training shorts. Lighter colours require fewer and less aggressive synthetic dyes. The more vibrant the colour, the higher the likely disperse dye load.
- Avoid moisture-wicking and stain-resistant marketing language without certification. These finishes often indicate PFAS treatment. If a brand cannot show you a third-party certification, assume the treatment is present.
- Wash new training gear before wearing. A significant portion of chemical residue is present in new garments from manufacturing. Washing removes some — but not all — surface-level chemical load.
- Shower immediately after training. Reduce the post-training window in which sweat-activated chemical migration can continue. Cold water preferred — it closes pores faster.
- Look for certifications: OEKO-TEX Standard 100, GOTS, bluesign, or EU Ecolabel. These are the only independent third-party verifications that mean anything. Brand claims of "eco-friendly" or "non-toxic" without certification are marketing, not evidence.
- Do not put polyester on your children. Infants and children show higher microplastic concentrations in faecal samples than adults. Their developing endocrine systems are the most vulnerable to chemical disruption. Cotton, wool, and certified natural fibres only for kids.
What Hard to Kill Looks Like From the Outside In
You cannot biohack your way out of a daily toxic load. No supplement corrects for chronic phthalate exposure. No ice bath undoes eight hours pressed against PFAS-treated polyester. The foundation of the Hard to Kill standard is removing what is actively degrading you — not just adding things that compensate for it.
Your ancestors wore linen, wool, and cotton. They did not have falling testosterone levels and epidemic male infertility. They also did not sleep, eat, and train wrapped in petroleum derivatives. The connection is not coincidental.
Start with your underwear. Then your rash guard. One change at a time — but start today.
Stay Dangerous. Stay on the Mats. Hard to Kill in Midlife.
