How Polyester Could Impact Reproductive Health

Modern medicine recognizes a variety of lifestyle factors that affect fertility, and clothing choice is gaining attention on that list. The main concerns with polyester and similar synthetic fabrics include:

• Overheating of Testicles: Polyester is not very breathable, which traps heat. Healthy sperm production requires the testes to stay slightly cooler than core body temperature (about 2–4°C lower) [7]. Even a minor increase in scrotal temperature can impair sperm formation and function [7]. Tight or non-breathable garments exacerbate this risk by preventing heat dissipation. Studies confirm that wearing snug, synthetic underwear can raise testicular temperature by roughly 0.5–0.8°C [7]. This may sound small, but it could be enough to inhibit spermatogenesis (sperm development) over time [7]. Notably, a large 2018 study of 656 men found those who primarily wore loose cotton boxer shorts had 25% higher sperm concentration and 17% higher total sperm count than men who wore tight-fitting underwear [9]. The boxer-wearing men also had significantly lower levels of follicle-stimulating hormone (FSH), suggesting their bodies weren’t straining to compensate for heat damage to the testes [9]. These findings underscore that cooler, breathable attire (like boxers or natural fabrics) can positively affect male fertility. By contrast, polyester’s heat-trapping nature may contribute to chronically warmer testicles and reduced sperm quality.

• Electrostatic Charge and Fabric Factors: Interestingly, the risks of polyester go beyond just heat. Research by Egyptian surgeon Dr. Ahmed Shafik in the 1990s explored fabric effects on fertility using both animal and human experiments. In one study, Shafik dressed two groups of dogs in underpants – one group in cotton, the other in polyester – for 24 months [1]. The polyester-wearing dogs showed a significant decrease in sperm count and motility and an increase in abnormal sperm forms, while the cotton-wearing dogs and a control group had no such changes [1]. The dogs’ semen parameters largely recovered after the polyester garment was removed, indicating the effect was reversible [1]. Strikingly, the testicular temperature did not differ significantly between the polyester and cotton groups in this study, since the garments were designed to be loose [1]. This led Shafik to propose that electrostatic charges generated by polyester fibers rubbing the skin might impair sperm production [1]. In a follow-up trial on humans, 14 healthy men wore a polyester sling around their scrotum continuously as a contraceptive test [2]. Amazingly, all men became azoospermic (zero sperm count) after about 140 days, effectively rendering them infertile until the sling was removed [2]. No hormonal changes were detected, again pointing to a local fabric effect [2]. Within several months after removing the polyester sling, the men’s sperm counts recovered to normal and their partners were able to conceive [2]. While these experiments are unusual and would need broader confirmation, they highlight that polyester’s impact on fertility is not just an old wives’ tale – the fabric itself can directly interfere with testicular function in some cases.

• Chemical Exposure from Synthetic Materials: Polyester is a form of plastic (polyethylene terephthalate), and synthetic textiles often contain a slew of chemical additives from manufacturing or finishing processes. These can include dyes, plasticizers, flame retardants, water-proofing agents, and more. Scientists are concerned that prolonged skin contact with such substances might introduce endocrine-disrupting chemicals (EDCs) into the body [5]. For instance, water-resistant polyester clothing may be treated with PFAS (per- and polyfluoroalkyl substances) – nicknamed “forever chemicals” – to repel stains or moisture. PFAS are notorious EDCs that accumulate in the body. According to the U.S. National Institute of Environmental Health Sciences, women with high blood levels of PFAS had up to 40% lower fertility, measured as reduced chances of pregnancy and live birth in one study [5]. PFAS exposure has also been linked to higher rates of endometriosis and polycystic ovary syndrome in women [5] – conditions that can cause infertility. Men are not off the hook either; many EDCs like PFAS or phthalates are suspected of contributing to declining sperm counts and quality in the general population [6]. Polyester fabrics can contain phthalates (used to make plastics soft and flexible) and residues of bisphenol-A (BPA) (used in some polyester-blend fibers and spandex) [5]. Both chemicals are proven endocrine disruptors. A 2021 review in a reproductive medicine journal found that higher concentrations of phthalates were associated with lower pregnancy rates and increased miscarriage incidence in couples [5]. Likewise, BPA exposure has been correlated with hormonal imbalances; for example, women with the highest BPA levels in their blood had a higher prevalence of PCOS, a hormone-driven infertility condition [5]. While it’s hard to pin these problems on clothing alone (people encounter phthalates and BPA from many sources like food packaging), the fact that polyester garments could leach such chemicals onto the skin is worrying. Over time, and especially when worn in tight contact with sensitive areas, synthetic fabrics might contribute to one’s overall chemical exposure load [5].

• Microplastics and Reproductive Health: An environmental angle to this issue is the release of microplastics – tiny fibers and particles – from synthetic clothing. Every time we wash or wear polyester, microscopic plastic fibers shed into water or air. These microplastics have now been detected in human blood, placentas, and even sperm fluid. Early research indicates they could act as yet another stressor on fertility. In animal studies, microplastic exposure led to reduced sperm counts and hormonal disruption [10]. A recent review in the American Journal of Men’s Health warned that microplastics may significantly degrade male semen quality and therefore “may be a significant cause of male infertility” [8]. The science on microplastics in human fertility is still nascent, but given that polyester is essentially a form of plastic, it’s reasonable to be cautious. Choosing natural fiber clothing helps reduce the microplastic burden on the environment and potentially on your body as well.