Microplastics are being found in human testes. Testosterone levels appear to be declining. And the clothes we train in are still overwhelmingly made from plastic. Here is what the latest science actually tells us.
Training is, at its core, a process of adaptation. We challenge the body to build muscle, improve metabolic health, protect long-term function and support the hormonal systems that make those adaptations possible.
Yet most of us do it wrapped almost entirely in plastic.
Polyester, nylon, acrylic and elastane dominate modern activewear because they are inexpensive, durable and easy to engineer. But they are also derived from fossil fuels, can shed microscopic plastic fibres and may carry chemical additives used to provide stretch, colour, moisture management, stain resistance and durability.
For years, questions about what that might mean for human health were easy to treat as abstract.
Now, they are becoming much harder to ignore.
Men’s testosterone levels are falling
In July 2026, researchers published the most extensive analysis yet of long-term testosterone trends.
The systematic review combined 12 studies, covering more than 102,000 men across seven countries between 1972 and 2019. It found significant declines in total testosterone, free testosterone and sex hormone-binding globulin.
Total testosterone declined by an estimated 0.26 nmol/L per year. The rate of decline was almost twice as fast in studies conducted after 2000.¹
That does not mean plastic clothing caused the decline.
Higher levels of body fat, diabetes, reduced physical activity, poor sleep, medication use and wider changes in metabolic health are all likely contributors. Environmental pollution and exposure to endocrine-disrupting chemicals are being investigated as additional factors, but their precise contribution remains unresolved.
What the study tells us is that something significant is happening.
The question is what role our increasingly plastic environment may be playing.
Plastic has already reached the human testicle
In 2024, researchers from the University of New Mexico examined testicular tissue from 23 men.
They found microplastics in every sample.
The average concentration was 328 micrograms per gram of tissue - almost three times the concentration found in canine testes examined alongside them.
Polyethylene was the most abundant polymer, but PVC, nylon, polyurethane, polypropylene and PET (the polymer used to make polyester) were also detected.²
This was a small study, and the researchers were explicit about its limitations. It did not measure testosterone or sperm production in the men, and finding plastic inside an organ does not prove that it is causing damage.
But it answered one important question.
Microplastics can reach the male reproductive system.
A 2025 study involving 200 men subsequently detected microplastics in 55.5% of semen samples. Frequent use of plastic tableware was associated with higher microplastic concentrations. Within certain subgroups - particularly frequent plastic-tableware users with a BMI below 24 - higher microplastic levels were associated with lower sperm concentrations.³
A further 2026 study again detected microplastics in human semen. In laboratory experiments, exposure to 500-nanometre polystyrene particles reduced sperm motility, increased oxidative stress, disrupted mitochondrial function and increased sperm DNA fragmentation. Supporting mouse experiments also found impaired sperm quality and effects on early embryo development.⁴
The human evidence remains observational. But the direction of travel is becoming increasingly difficult to ignore.
Conceptual illustration of testosterone-producing cells and environmental microplastic exposure.
What microplastics do to testosterone in experimental studies
Testosterone is produced predominantly by Leydig cells inside the testes.
Experimental research suggests that microplastics may interfere with this process through several overlapping mechanisms:
- oxidative stress
- inflammation
- mitochondrial damage
- disruption of the blood–testis barrier
- damage to Leydig and Sertoli cells
- interference with the hormonal signalling that controls testosterone production
A February 2026 study exposed male rats to low oral doses of polystyrene microplastics for 45 days.
The researchers reported dose-dependent reductions in testosterone, sperm count and sperm motility. They also observed increased abnormal sperm, inflammation, depleted antioxidant defences, mitochondrial dysfunction and visible damage to testicular tissue. Microplastics were detected in the testes at the higher exposure levels.⁵
A separate 2024 mouse study found that chronic exposure to polystyrene microplastics reduced testosterone and impaired steroid production in Leydig cells. The researchers identified mitochondrial oxidative stress and increased cell death as possible mechanisms.⁶
These studies provide biological plausibility - not proof that the same effects occur in men at normal environmental exposure levels.
Humans are not rats. Laboratory particles are not identical to the complex mixture of fibres and chemicals encountered in real life. Exposure routes and doses also vary enormously.
But when microplastics are present in human testes and repeated experimental studies show that these particles can damage the cells responsible for testosterone production, it is reasonable to take the possibility seriously.
The particle is only part of the story
Plastic is not simply an inert material.
A finished synthetic garment may contain dyes, plasticisers, bisphenols, PFAS, UV stabilisers, flame retardants and other finishing chemicals. Some are deliberately applied. Others are contaminants or by-products of manufacturing and recycling.
Of particular concern are endocrine-disrupting chemicals: substances capable of imitating, blocking or interfering with the body’s hormones.
Phthalates are used to make certain plastics softer and more flexible. A systematic review of human epidemiological evidence found robust evidence connecting exposure to DEHP and DBP - two types of phthalate - with adverse male reproductive outcomes.
For DEHP, the evidence included associations with changes in testosterone and semen parameters at exposure levels found in the general population.⁷
Bisphenol A, or BPA, can interact with both oestrogen and androgen signalling. A 2024 systematic review and meta-analysis concluded that BPA exposure can disrupt reproductive hormones and reduce sperm counts, although results between individual human studies were not completely consistent.⁸
PFAS (often called “forever chemicals”) are sometimes used to provide water, oil and stain resistance.
A recent analysis of US health data found associations between certain PFAS compounds and an increased likelihood of low testosterone in some groups of men.⁹ However, other population studies have reported higher testosterone concentrations or no clear relationship.
The results appear to differ according to the individual chemical, exposure level, age and population being studied.¹⁰
The honest conclusion is not that every synthetic garment contains every one of these substances.
It is that clothing labels tell us almost nothing about the complete chemical formulation of the material worn against our skin.
Polyester begins as a petrochemical. Oil is processed into polymers, spun into continuous filament yarn and knitted into fabric.
What has actually been found in clothing?
In 2024, researchers analysed 57 conventional and recycled textile samples for BPA and related bisphenols.
BPA concentrations ranged from below the detection threshold to 625 nanograms per gram. BPS concentrations reached 2,474 nanograms per gram.
Recycled textiles had almost twice the median BPA concentration of conventional textiles.
Most importantly for activewear, estimated exposure from dry material remained below the European Food Safety Authority’s tolerable daily intake. But when researchers modelled wet fabric - simulating sweat or humidity - estimated BPA exposure frequently exceeded it.¹¹
Separate testing by the US Center for Environmental Health has reported BPA in polyester-and-spandex sports bras and athletic shirts. Some products were alleged to expose wearers to as much as 22 times California’s permitted safe level of BPA.¹²
These studies demonstrate that surprisingly high concentrations of an endocrine-disrupting chemical can occur in real activewear products.
Why sweat changes the equation
Skin is a barrier, but it is not an impenetrable wall.
Activewear presents an unusual exposure scenario: close-fitting material, a large area of skin, heat, movement, friction and prolonged sweating.
In 2024, researchers used a three-dimensional human skin model to study flame-retardant chemicals carried by polyethylene and polypropylene microplastics.
Up to 8% of the chemical exposure dose became available at the skin surface, while no more than 0.1% passed completely through the skin model. Crucially, sweaty skin made the chemicals more bioavailable than dry skin.¹³
Another human-skin-model study examined 17 PFAS compounds. Fifteen either crossed into or accumulated within the skin.
Short-chain PFAS were absorbed most readily, with two compounds showing absorption of approximately 49% and 59% under the laboratory conditions.¹⁴
Those experiments applied isolated chemicals under controlled laboratory conditions. They do not tell us what percentage transfers from a particular T-shirt during an hour-long workout.
However, a 2025 study brought the question closer to real textiles.
Researchers found PFAS and organophosphate esters in children’s garments and household fabrics, then modelled dermal transfer under dry and sweaty conditions. Sweat increased estimated dermal absorption by as much as 3,252-fold for certain PFAS and 835-fold for certain organophosphate esters compared with dry contact.¹⁵
These are relative increases from a low dry baseline. They are not evidence that thousands of times more chemical necessarily enters an athlete’s bloodstream during a real workout.
But the finding reinforces an important point:
The moment when synthetic activewear is expected to perform at its best - hot, wet and pressed tightly against the body - may also be the moment when chemicals within it are most available for transfer.
Conceptual illustration of sweat at the interface between synthetic fabric and skin.
Does synthetic activewear lower testosterone?
No controlled human study has taken two groups of men, placed one in polyester activewear and the other in natural-fibre clothing, and demonstrated a resulting difference in testosterone.
We also cannot trace the microplastics found in a man’s testes back to his gym kit.
Food, drinking water, household dust, packaging, air pollution and countless other plastic products all contribute to our exposure. For most people, ingestion and inhalation may remain more significant exposure routes than clothing.
What we can say is this:
- Some synthetic textiles contain endocrine-disrupting chemicals.
- Chemicals and additives can migrate out of plastic materials.
- Sweat can increase their release and bioavailability.
- Some of these chemicals can cross or accumulate within human skin.
- Microplastics are being found in human testes and semen.
- Experimental exposure can reduce testosterone and impair sperm health.
- The long-term effect of wearing plastic-based clothing against sweating skin has not been adequately studied.
Absence of definitive proof is not the same as proof of safety.
A precaution - not a panic
There is no reason to believe that wearing a polyester T-shirt for one workout will crash your testosterone. Hormonal health is shaped by the whole picture: body composition, sleep, diet, alcohol, stress, medication, age, physical activity and metabolic health.
Clothing is one part of a much larger system.
But it is also one of the few exposures over which we have immediate control.
Men who want to reduce unnecessary exposure can:
- choose garments made predominantly from natural or cellulosic fibres;
- avoid unnecessary stain-resistant, water-repellent and “anti-odour” treatments;
- wash new clothing before wearing it;
- avoid remaining in sweat-saturated synthetic clothing after training;
- look for transparent material and chemical certifications;
- reduce plastic exposure through food storage, drinking water and household dust as well as clothing.
Why Airoc starts with natural fibres
At Airoc, we do not claim that natural activewear is a medical treatment. Nor do we pretend that every synthetic garment is inherently dangerous.
We are also not claiming that every Airoc garment is completely plastic-free. Some products still require a small proportion of elastane to provide the stretch, recovery and durability activewear demands.
But there is an enormous difference between using a limited amount of stretch fibre where it is necessary and making the entire garment from plastic.
Our position is simple.
When clothing is worn tightly against the body, heated, stretched and saturated with sweat, the material matters.
If we can achieve performance with natural fibres forming the foundation - rather than wrapping the body almost entirely in petrochemical plastic - that feels like the more intelligent direction.
We should not have to wait until every mechanism has been proven beyond doubt before questioning why the clothes designed to support human health are made almost entirely from fossil fuels.
We are already living through the experiment.
We are simply beginning to see the results.
References
¹ Levy A, Hansen LS, Abu Ahmad W, et al. “Temporal trends in total and free testosterone (1972–2019): a systematic review and meta-trend analysis.” Human Reproduction. 2026;41(Supplement 1).202. https://doi.org/10.1093/humrep/deag083.202
² Hu CJ, Garcia MA, Nihart A, et al. “Microplastic presence in dog and human testis and its potential association with sperm count and weights of testis and epididymis.” Toxicological Sciences. 2024;200(2):235–240. https://doi.org/10.1093/toxsci/kfae060
³ Qu J, Zeng J, Mou L, Wu X, Ha M, Liu C. “Plastic tableware use, microplastic accumulation, and sperm quality: from epidemiological evidence to FOXA1/p38 mechanistic insights.” Journal of Nanobiotechnology. 2025;23:634. https://doi.org/10.1186/s12951-025-03747-7
⁴ Ren F, Pei J, Li L, et al. “The presence of microplastics in human semen and the protective role of nicotinamide mononucleotide against polystyrene nanoplastics-induced reproductive and early embryonic toxicity.” Journal of Hazardous Materials. 2026;505:141557. https://doi.org/10.1016/j.jhazmat.2026.141557
⁵ Alsenousy AHA, Khalaf AHY, Ibrahim HZ, Kamel MA, Yousef MI. “Impact of polystyrene microplastic exposure at low doses on male fertility: an experimental study in rats.” Scientific Reports. 2026;16:7474. https://doi.org/10.1038/s41598-026-38385-y
⁶ Liu Y, Li X, Xiong Y. “Chronic polystyrene microplastic exposure reduces testosterone levels in mice through mitochondrial oxidative stress and BAX/BCL2-mediated apoptosis.” Toxics. 2024;12(8):561. https://doi.org/10.3390/toxics12080561
⁷ Radke EG, Braun JM, Meeker JD, Cooper GS. “Phthalate exposure and male reproductive outcomes: a systematic review of the human epidemiological evidence.” Environment International. 2018;121:764–793. https://doi.org/10.1016/j.envint.2018.07.029
⁸ Lü L, Liu Y, Yang Y, He J, Luo L, Chen S, Xing H. “Bisphenol A exposure interferes with reproductive hormones and decreases sperm counts: a systematic review and meta-analysis of epidemiological studies.” Toxics. 2024;12(4):294. https://doi.org/10.3390/toxics12040294
⁹ Rahman HH, Stokey WR, et al. “Correlation of per- and poly-fluoroalkyl substances exposure with testosterone levels in the male population.” Environmental Toxicology and Pharmacology. 2026;121:104906. https://doi.org/10.1016/j.etap.2025.104906
¹⁰ Xie X, Weng X, Liu S, et al. “Perfluoroalkyl and polyfluoroalkyl substance exposure and association with sex hormone concentrations: results from the NHANES 2015–2016.” Environmental Sciences Europe. 2021;33. https://doi.org/10.1186/s12302-021-00508-9
¹¹ Jurikova M, Dvorakova D, Bechynska K, Pulkrabova J. “Bisphenols in daily clothes from conventional and recycled material: evaluation of dermal exposure to potentially toxic substances.” Environmental Science and Pollution Research. 2024;31:55663–55675. https://doi.org/10.1007/s11356-024-34904-4
¹² Center for Environmental Health. “New Testing Shows High Levels of BPA in Sports Bras and Athletic Shirts.” 12 October 2022. https://ceh.org/latest/press-releases/new-testing-shows-high-levels-of-bpa-in-sports-bras-and-athletic-shirts/
¹³ Abafe OA, Harrad S, Abdallah MAE. “Assessment of human dermal absorption of flame-retardant additives in polyethylene and polypropylene microplastics using 3D human skin equivalent models.” Environment International. 2024;186:108635. https://doi.org/10.1016/j.envint.2024.108635
¹⁴ Ragnarsdóttir O, Abdallah MAE, Harrad S. “Dermal bioavailability of perfluoroalkyl substances using in vitro 3D human skin equivalent models.” Environment International. 2024;188:108772. https://doi.org/10.1016/j.envint.2024.108772
¹⁵ Li K, Sun X, Qian Y, et al. “Sweat-amplified dermal transfer and combined toxicity of per- and polyfluoroalkyl substances and organophosphate ester mixtures in children’s textiles.” Science of the Total Environment. 2025;1000:180426. https://doi.org/10.1016/j.scitotenv.2025.180426
This article is provided for general educational purposes and does not constitute medical advice. Anyone concerned about testosterone levels, fertility or hormonal health should speak with a qualified healthcare professional.