No credible evidence shows that wearing ordinary polyester clothing causes infertility. The concern traces back to a handful of striking experiments from the 1980s and 1990s, in which polyester garments worn directly against the scrotum appeared to suppress sperm production in both dogs and men. Those studies generated headlines, but their designs involved specific conditions that don’t map neatly onto everyday clothing use. The fuller picture involves electrostatic charges, scrotal temperature, chemical residues, and microplastics, and the honest answer is more layered than a simple yes or no.
The Dog Underwear Study and Its Human Follow-Up
The research most often cited in online discussions comes from Egyptian urologist Ahmed Shafik, who published a series of experiments spanning the 1980s and 1990s. In one study, 24 dogs were divided into groups wearing either cotton or polyester underwear continuously for 24 months, with a control group wearing nothing. By the end of the trial, the polyester group showed a significant drop in sperm count and motility, along with a rise in abnormal sperm forms. Testicular biopsies revealed degenerative changes. After the garments were removed, sperm quality gradually returned to normal in most of the dogs, though two out of twelve remained with low counts.1PubMed. Effect of different types of textile fabric on spermatogenesis: an experimental study
Shafik then tested the concept in humans. Fourteen men wore a polyester scrotal sling (essentially a polyester suspensory pouch held snugly against the scrotum) continuously. All of them became azoospermic, meaning their semen contained no detectable sperm, after an average of about 140 days. No pregnancies occurred during the wearing period. Like the dog study, the effect appeared reversible after the sling was removed.2Contraception. Contraceptive efficacy of polyester-induced azoospermia in normal men
These results sound alarming, but context matters. The slings were worn continuously, pressed directly against the scrotal skin, around the clock for months. That’s quite different from wearing a polyester-blend shirt or even polyester boxer briefs for part of the day. The studies were also small, conducted by the same research group, and have not been replicated by independent teams. Shafik himself framed the polyester sling as a potential male contraceptive, not as evidence that wearing polyester clothing in general threatens fertility.
Electrostatic Fields on the Scrotum
Shafik’s proposed explanation for why polyester affected sperm production was unusual: he believed that polyester fabric generates electrostatic charges against the skin, and that those charges interfere with the cells responsible for making sperm. In a companion study, he measured electrostatic potentials on the scrotal surface of men wearing different fabrics. Polyester underwear generated the highest readings, averaging about 339 volts per square centimeter. A cotton-polyester blend produced less than half that level.3PubMed. Effect of different types of textile fabric on spermatogenesis: electrostatic potentials generated on the surface of the human scrotum by wearing different types of fabric In the human sling trial, the polyester suspensory generated similar electrostatic potentials, averaging around 366 volts per square centimeter during the day and about 158 at night.2Contraception. Contraceptive efficacy of polyester-induced azoospermia in normal men
The theory is intriguing but remains unproven. No other research group has confirmed that electrostatic fields of this magnitude actually disrupt testicular function at the cellular level. Static buildup on clothing is real and measurable, but the leap from “polyester produces static” to “static kills sperm” hasn’t been established through independent replication or a clear biological mechanism. The idea sits in a scientific gray zone: not debunked, but not supported by enough evidence to take at face value.
Heat, Tightness, and Underwear Style
A more widely studied factor in male fertility is scrotal temperature. The testes hang outside the body for a reason: sperm production works best a couple of degrees below core body temperature. Anything that heats the scrotum for prolonged periods, whether tight clothing, prolonged sitting, or hot tub use, can theoretically reduce sperm quality. Tight-fitting undergarments can raise scrotal temperature by roughly 1°C, according to controlled measurements.4PubMed Central. Garment fit, scrotal thermoregulation, and male fertility outcomes: a narrative review
This is where polyester’s poor breathability enters the conversation. Polyester wicks moisture differently from cotton. Moisture accumulation in fabric layers depends directly on the fiber type of the underwear being worn.5Textile Research Journal. Determination of the effect of fabric properties on the coupled heat and moisture transport of underwear–shirt fabric combinations In theory, a tight polyester garment could trap more heat and moisture against the groin than a loose cotton one. But the operative word here is “tight.” The fabric matters less than the fit.
A preconception cohort study that followed couples trying to conceive found that men’s underwear choice was associated with only minor differences in semen parameters, and after statistical correction for multiple comparisons, none of the differences remained significant. More importantly, there was no association between underwear type and time to pregnancy or infertility.6PubMed Central. Choice of underwear and male fecundity in a preconception cohort of couples That finding provides useful reassurance: for men in everyday situations, underwear fabric alone doesn’t appear to meaningfully shift the odds of conception.
Chemical Residues in Polyester Fabric
The fertility question gets more interesting when you look beyond the fabric itself and consider what’s in it or on it. Polyester (polyethylene terephthalate, or PET) is manufactured using antimony trioxide as a catalyst. Antimony residues remain in the finished fabric and can migrate to the skin, especially through sweat. A study measuring trace elements in skin-contact clothing found high concentrations of antimony in polyester fabrics. One polyester T-shirt exceeded the safety limit for dermal exposure, and the researchers noted that frequent, prolonged wearing of polyester could pose health risks for certain groups.7Textile Research Journal. Trace elements in skin-contact clothes and migration to artificial sweat: Risk assessment of human dermal exposure A separate assessment using a different methodology found that antimony’s non-carcinogenic risk from polyester clothing was above 10% of the safety threshold, and while it fell below the level considered dangerous for most adults, it warranted monitoring.8Environmental Research. Human exposure to trace elements through the skin by direct contact with clothing: Risk assessment
Textiles also accumulate phthalates from the surrounding environment. Both cotton and polyester fabrics absorb these chemicals from indoor air over time. In one experiment, over 30 days cotton fabrics accumulated higher total phthalate levels than polyester (roughly 3,475 versus 1,950 nanograms per square decimeter), and the researchers flagged the results as relevant to dermal exposure.9PubMed. From Clothing to Laundry Water: Investigating the Fate of Phthalates, Brominated Flame Retardants, and Organophosphate Esters Another study found that phthalate levels on skin covered by clothing were lower than on bare skin, but still substantial enough that ignoring covered areas would underestimate total dermal uptake by a factor of two to five.10PubMed. Impact of Clothing on Dermal Exposure to Phthalates: Observations and Insights from Sampling Both Skin and Clothing
Water-repellent coatings and stain treatments on clothing can also contain PFAS (per- and polyfluoroalkyl substances), another class of chemicals linked to endocrine disruption. A recent review covering evidence from 2019 to 2025 identified elevated health risks from phthalates in infant clothing and PFAS in water-repellent fabrics as key concerns.11PubMed. Human health risks from textile chemicals: a critical review of recent evidence (2019-2025) Sweat dramatically amplifies absorption: a study on children’s textiles found that sweating increased chemical transfer from fabric to skin by up to several thousand-fold for PFAS compared to dry contact.12Science of The Total Environment. Sweat-amplified dermal transfer and combined toxicity of per- and polyfluoroalkyl substances and organophosphate esters mixtures in children’s textiles
Do These Chemicals Actually Harm Fertility?
Phthalates are classified as endocrine disruptors, meaning they can interfere with hormone signaling. In laboratory and animal studies, most phthalates disrupt the genes involved in steroid hormone production in fetal Leydig cells, the testicular cells responsible for making testosterone.13PubMed Central. Phthalate-Induced Fetal Leydig Cell Dysfunction Mediates Male Reproductive Tract Anomalies Environmental endocrine disruptors more broadly have been shown to cause Leydig cell death and premature aging in lab settings.14PubMed Central. The Role of Environmental Endocrine Disruptors on Leydig Cell Death and Senescence
For women, the picture is mixed. One study of women seeking infertility care found that exposure to common phthalate mixtures was inversely associated with antral follicle count (a marker of ovarian reserve), suggesting a roughly 9% decline in follicle count associated with higher combined phthalate exposure.15Science of The Total Environment. Phthalate and DINCH exposure and ovarian reserve markers among women seeking infertility care Some individual phthalate metabolites have shown associations with changes in follicle count in other studies, though the direction of the effect varied depending on the specific metabolite.16Ecotoxicology and Environmental Safety. The association of serum phthalate metabolites with biomarkers of ovarian reserve in women of childbearing age Meanwhile, a study specifically looking at women with PCOS-related infertility found no significant link between endocrine-disrupting chemical exposure and ovarian reserve markers.17PubMed. Plasticizer exposure and reproductive dysfunction: Assessing bisphenol A and phthalate esters impact on ovarian reserve in women with PCOS-associated infertility
The critical gap here is dose. These studies measure phthalate exposure from all sources combined: food packaging, cosmetics, flooring, dust, and yes, clothing. No study has isolated the contribution of polyester fabric to total phthalate or antimony exposure and then linked that specific contribution to a fertility outcome. The chemicals in and on polyester are real, their reproductive effects in lab studies are real, but the dose delivered through wearing a polyester shirt or pair of pants is a fraction of what most people absorb from other sources in a typical day.
Microplastics and Reproductive Tissue
Polyester is the largest source of microplastic fiber shedding in laundry, and those fibers end up in water, food, and air. But microplastics also enter the body through ingestion and inhalation, and recent research has shown that micro- and nanoplastic particles can cross several biological barriers, including the blood-testis barrier.18Environment & Health. Human Exposure to Micro- and Nanoplastics: Trans-Barrier Transport, Tissue Accumulation, and Health Risks In lab cell studies, PET micro- and nanoplastics have caused dose-dependent toxicity, increased oxidative stress, and DNA damage markers in exposed cells.19PubMed Central. Engineered and Weathered Polyethylene Terephthalate (PET) Microplastics and Nanoplastics Induce Form and Size-Dependent Oxidative Stress, Oxidative DNA Damage, and Cytotoxicity in MCF-7 Cells
This line of research is newer and mostly preclinical. Nobody has yet demonstrated that wearing polyester clothing increases microplastic accumulation in reproductive tissues at levels that impair fertility in living humans. The concern is plausible on a mechanistic level: the particles can get there, and once there they can cause cellular stress. But the jump from cell culture experiments to real-world fertility effects is enormous, and extrapolating from one to the other is premature. Researchers themselves tend to flag this as an area needing far more study before any public health conclusions can be drawn.
Factory Workers Face a Different Risk
One population where textile-related reproductive harm has been documented is workers in synthetic-fiber manufacturing plants. A study of women textile workers in Shanghai found that exposure to synthetic fiber dust during pregnancy was associated with a meaningfully elevated risk of miscarriage. The risk was roughly doubled for women exposed to synthetic fibers and more than tripled for those exposed to mixed synthetic and natural fiber dust, compared to unexposed workers.20PubMed Central. Dust and Chemical Exposures, and Miscarriage Risk Among Women Textile Workers in Shanghai, China
This is an important distinction that often gets lost in online discussions. Breathing in concentrated synthetic fiber dust and chemical fumes in a factory for hours every day is a fundamentally different exposure pathway than wearing a finished garment. The manufacturing environment involves raw chemical intermediates, solvents, dye carriers, and airborne particulates at concentrations orders of magnitude higher than anything that migrates through finished fabric to skin. When someone cites textile-related fertility risks, it’s worth asking whether the study involved consumers wearing clothes or workers producing them.
What Actually Matters for Everyday Clothing Choices
If you’re trying to conceive and wondering whether your wardrobe is working against you, the evidence points toward a few practical considerations rather than a blanket avoidance of polyester. Fit matters more than fabric for scrotal temperature: loose-fitting underwear of any material keeps the scrotum cooler than tight briefs. Washing new clothes before wearing them reduces the initial load of processing chemicals, dyes, and finishes, regardless of fiber type. Choosing garments without water-repellent or stain-resistant treatments cuts your exposure to PFAS.
The original polyester-sling experiments are fascinating as curiosities of reproductive research, but they describe a scenario far removed from normal clothing use. No human study has shown that wearing ordinary polyester garments in a typical daily rotation leads to reduced fertility. The chemical exposures from polyester (antimony, phthalates absorbed into fibers, potential microplastic shedding) are genuine, but they are small contributors within a much larger landscape of environmental chemical exposure from food, personal care products, and household items.
Why Polyester Gets Singled Out
Polyester’s reputation as a fertility threat owes a lot to how science gets communicated on the internet. Shafik’s studies are dramatic: dogs wearing polyester underwear, men rendered sperm-free by a polyester jockstrap. Those are the kind of findings that get shared widely, stripped of their context. The nuance that the sling was worn 24 hours a day in direct scrotal contact for months, or that no independent group replicated the results, rarely makes it into the headline. Meanwhile, cotton absorbs more phthalates from indoor air than polyester does, antimony exposure from polyester falls below safety limits for most adults in most assessments, and the only study directly comparing underwear types in couples trying to get pregnant found no effect on conception timing.6PubMed Central. Choice of underwear and male fecundity in a preconception cohort of couples
None of this means polyester is completely benign. The accumulating evidence on endocrine disruptors, microplastics, and textile chemicals deserves serious attention, and there are legitimate reasons researchers continue to study how synthetic fabrics interact with the body. But the specific claim that wearing polyester causes infertility outpaces what the science has actually shown. The more accurate framing is that polyester, like many synthetic materials, is part of a broader chemical environment that researchers are still working to understand, and the contribution of any single garment to your total exposure remains very small.