Polyester and Fertility: What Three Decades of Peer-Reviewed Research Actually Shows
Fertility rates are declining globally. That much is no longer debated. In 2022, a meta-analysis led by Professor Hagai Levine of Hebrew University — published in Human Reproduction Update and spanning data from 53 countries — confirmed that sperm concentrations have dropped more than 50% since the early 1970s, with the rate of decline accelerating after the year 2000. The causes remain multifactorial and not fully understood, but researchers have increasingly turned their attention toward environmental exposures, including the materials we wear against our skin every day.
Among those materials, polyester — a plastic polymer derived from polyethylene terephthalate (PET) — has attracted a surprising volume of peer-reviewed scrutiny. The research is imperfect, as all early-stage inquiry tends to be. But dismissing it outright would mean ignoring a body of evidence that stretches across three decades and includes human trials, controlled animal studies, large-scale epidemiological data, and emerging work on microplastics in reproductive tissue.
Here is what the published science actually says.
The Shafik Studies: Direct Textile-to-Fertility Research (1992–2008)
The most frequently cited research on polyester and reproductive function comes from the laboratory of Professor Ahmed Shafik at the Faculty of Medicine, Cairo University. Shafik, a prolific pelvic surgeon who published approximately 500 studies in his career, conducted a series of controlled experiments that remain the most direct investigation into the relationship between textile type and fertility.
The 1992 human trial
Published in Contraception (Volume 45, Issue 5), Shafik's 1992 study enrolled 14 healthy men who wore a polyester scrotal sling continuously. Over the course of 12 months, the study tracked semen parameters, testicular volume, rectal-testicular temperature differential, serum reproductive hormones, testicular biopsy results, and the electrostatic potentials generated between the polyester fabric and scrotal skin.
The results were unambiguous within the study population: all 14 participants became azoospermic — producing zero measurable sperm — after an average of approximately 140 days. Testicular volume decreased, and the rectal-testicular temperature differential narrowed. After the sling was removed, sperm production returned to pre-study levels within an average of roughly 157 days. Shafik proposed two mechanisms: the creation of an electrostatic field across intrascrotal structures, and disordered thermoregulation.
The 1993 canine study
Published in Urological Research (Volume 21, pages 367–370), this companion study divided 24 dogs into two groups: one wearing cotton underpants and the other wearing polyester. An additional seven dogs wore nothing and served as controls. The garments were deliberately fitted loosely around the scrotum to isolate the effect of the fabric from simple compression or insulation.
Over 24 months of continuous wear, the polyester group showed significant decreases in sperm count and sperm motility, along with increases in abnormal sperm morphology. Testicular biopsies revealed degenerative changes. After the polyester garments were removed, semen parameters returned to normal in 10 of the 12 dogs; two remained oligozoospermic. The cotton group and control group showed no significant changes throughout the entire 36-month study period.
Notably, testicular temperature in the polyester group did not change significantly during the study, suggesting that heat alone did not explain the observed effects. Shafik pointed again to electrostatic potentials generated by the polyester fabric as a plausible contributing mechanism.
The electrostatic measurement study
In a related investigation, Shafik measured the electrostatic potentials generated on the scrotal surface when 21 men wore underwear made from 100% polyester, 100% cotton, or a 50/50 polyester-cotton blend. The polyester pants generated the highest electrostatic potentials, the blend produced roughly half that level, and cotton generated none. This study gave quantitative support to the hypothesis that fabric-generated static electricity may interfere with normal testicular function.
The 2008 female canine study
Less widely cited but relevant, Shafik also investigated the effect of fabric type on female reproductive function. In this study, 35 female dogs wore undergarments made from polyester, polyester-cotton blends, cotton, or wool for 12 months. The dogs wearing polyester and polyester-blend garments showed decreased progesterone levels during their reproductive cycles and failed to conceive through both natural mating and insemination. Electrostatic fields were again detected on the skin of the polyester-wearing dogs. As with the male studies, the effects were reversible after the garments were removed.
Limitations of the Shafik research
Transparency about what these studies do and do not prove is essential. The sample sizes were small (14 men in the human trial, 24 dogs in the canine study). The 1992 human study used a specially constructed polyester sling worn continuously — not conventional polyester underwear worn on a typical daily cycle. No subsequent research team has replicated the Shafik studies with comparable methodology, and the electrostatic mechanism, while plausible and measurable, has not been validated through independent confirmation. The studies are now three decades old.
None of this invalidates the findings. It does mean they should be interpreted as strong signals warranting further investigation rather than definitive proof of clinical harm from everyday polyester garments.
The Harvard Underwear Study: Scale and Modern Epidemiology (2018)
The largest study to date examining the relationship between underwear type and testicular function was published in Human Reproduction (Volume 33, Issue 9) in August 2018. Led by Dr. Lidia Mínguez-Alarcón at Harvard T.H. Chan School of Public Health and conducted at the Fertility Clinic at Massachusetts General Hospital, the study enrolled 656 male partners of couples seeking infertility treatment between 2000 and 2017.
Men who reported most frequently wearing boxers had significantly higher sperm concentrations and total sperm counts compared to men who primarily wore tighter-fitting underwear. They also had lower levels of follicle-stimulating hormone (FSH), a finding consistent with a compensatory mechanism: when the testes are under thermal stress, the hypothalamus increases FSH secretion in an attempt to stimulate sperm production.
The study did not isolate fabric type from fit. It could not determine whether the observed effects were driven by compression, heat retention, material composition, or some combination. But it provided the first large-scale, statistically rigorous confirmation that what men wear against their reproductive organs appears to affect measurable markers of testicular function. The authors noted that their study was the first to go beyond traditional semen analysis to include hormonal markers and sperm DNA fragmentation data.
Chemical Exposure: What Polyester Carries Beyond the Fiber
Research attention has expanded beyond the physical properties of polyester fabric to the chemical compounds it introduces. Polyester is manufactured from PET resin, a process that typically involves antimony trioxide as a catalyst. The finished fabric may also contain residues of bisphenol A (BPA), phthalates (used as plasticizers), and per- and polyfluoroalkyl substances (PFAS) applied as stain-resistant or water-repellent finishes. Each of these chemical families has an established body of evidence connecting it to endocrine disruption.
Phthalates function as anti-androgens. They interfere with testosterone production and have been associated with reduced fertility in both men and women. A 2021 review in Best Practice & Research Clinical Endocrinology & Metabolism found that higher phthalate concentrations were associated with decreased pregnancy rates and increased miscarriage incidence in couples.
BPA mimics estrogen. Elevated BPA levels have been correlated with hormonal imbalances, including a higher prevalence of polycystic ovary syndrome (PCOS) in women and altered semen parameters in men. Research has linked BPA exposure to decreased egg quality and disrupted ovulation.
PFAS — sometimes called "forever chemicals" because they do not break down in the environment — have been connected to reduced fertility in women by as much as 40%, according to research referenced by the NIH's National Institute for Environmental Health Sciences.
Dr. Audrey Gaskins, an associate professor of environmental health at Emory University, has noted that most research focuses on specific chemicals measured in blood or urine rather than on fabrics directly. This distinction matters. The pathway from fabric to systemic chemical exposure involves migration through sweat and skin absorption, and the dose delivered through clothing alone — versus food packaging, drinking water, and other environmental sources — has not been precisely quantified.
What can be said is that polyester garments represent one of several daily sources of known endocrine-disrupting compounds, and that the chemicals involved have documented reproductive effects at the concentrations found in general-population biomonitoring.
Microplastics in Reproductive Tissue: An Emerging Body of Evidence
Perhaps the most rapidly developing area of research involves microplastics — plastic particles smaller than 5mm — and their presence in the human reproductive system. Polyester fabric sheds microplastic fibers during both washing and wearing. These fibers enter the body through ingestion, inhalation, and dermal absorption.
In 2024, a study published in Toxicological Sciences (Volume 200, Issue 2) by Hu et al. at the University of New Mexico quantified microplastics in both canine and human testicular tissue. The average concentration of total microplastics in human testes was roughly three times higher than in canine testes. Polyethylene and PVC were the dominant polymer types. Significant negative correlations were observed between canine testis weight and concentrations of specific plastics, though the authors were careful to note that correlation does not establish causation.
A 2024 multi-site study across China, published in eBioMedicine, analyzed semen and urine samples from 113 men and identified eight types of microplastics. PTFE exposure was specifically associated with reduced sperm quality after adjusting for age, BMI, smoking, alcohol consumption, and collection site.
In 2025, a study of 45 men published in Toxics reported microplastics in approximately 76% of semen samples, with an average abundance of 17 particles per gram. PET — the polymer from which polyester fabric is made — was the most prevalent type, representing roughly 36% of all particles detected. Participants exposed to PET showed trends toward lower progressive motility, though sample sizes limit the statistical power of this finding.
Also in 2025, research presented at the 41st Annual Meeting of the European Society of Human Reproduction and Embryology reported detecting microplastics in 55% of seminal fluid samples and 69% of follicular fluid samples from women, further broadening the conversation beyond male fertility alone.
An in vitro study published in Toxics in July 2025 exposed human sperm directly to polystyrene microplastics. Sperm vitality and motility decreased in a time-dependent manner, and the researchers observed increases in oxidative stress, DNA fragmentation, and reactive oxygen species production.
These findings are still early-stage. Contamination control in microplastics research is methodologically challenging, and some studies — including Hu et al. — have faced peer-reviewed critique regarding analytical rigor. But the pattern of detection across multiple independent research groups, geographies, and tissue types makes it increasingly difficult to dismiss the presence of microplastics in reproductive tissue as an artifact.
The Female Side: Understudied but Not Empty
Direct research on polyester fabric and female fertility is substantially thinner than the male-focused literature. Beyond Shafik's 2008 female canine study, no controlled trials have examined the effect of synthetic underwear on women's reproductive outcomes.
The relevant evidence for women is therefore largely indirect, drawn from the broader endocrine disruption literature. Phthalates have been linked to disrupted estrogen production and impaired ovulation. BPA exposure has been associated with decreased egg quality and a higher prevalence of PCOS. Several studies have suggested a connection between phthalate exposure and increased risk of endometriosis. Microplastics have now been detected in human follicular fluid and placental tissue.
These data points do not prove that wearing polyester causes female infertility. They do establish that the chemical compounds carried by polyester fabrics have documented effects on female reproductive biology, and that those compounds reach reproductive tissue. This is sufficient to warrant attention, if not alarm.
What the Research Does Not Say
Scientific integrity requires being as clear about what the evidence does not show as what it does.
No large-scale, randomized controlled trial has demonstrated that wearing conventional polyester clothing causes clinical infertility in men or women. The Shafik studies, while striking in their results, used atypical conditions (continuous sling wear, small sample sizes) that do not map directly onto typical underwear habits. The Harvard study could not separate the effects of fabric type from garment fit. The microplastics research establishes presence and suggests biological plausibility but has not yet demonstrated a clear dose-response relationship in human fertility outcomes. Chemical migration from fabric through skin remains quantitatively uncertain relative to other exposure pathways.
Multiple fertility specialists — including Dr. Alex Robles of Columbia University Fertility Center and Dr. Jaime Knopman of CCRM Fertility New York — have stated publicly that they have not observed strong clinical evidence that underwear fabric alone has a meaningful, isolated impact on fertility outcomes.
What the Research Does Say
Taken together, the published literature establishes several findings that have been replicated or corroborated across independent studies:
Polyester fabric generates measurable electrostatic fields against skin that are not produced by cotton, and that have been associated with impaired spermatogenesis in both human and animal models. Tight-fitting, synthetic underwear is associated with reduced sperm concentrations and hormonal changes consistent with testicular stress in the largest epidemiological study conducted on the subject. Polyester production and finishing processes introduce compounds — antimony, BPA, phthalates, PFAS — with documented endocrine-disrupting properties and established links to impaired fertility in both sexes. Polyester fabric sheds microplastic fibers that have now been detected in human testicular tissue, semen, follicular fluid, placental tissue, and blood — with PET being among the most prevalent polymer types found. In vitro exposure of human sperm to microplastics reduces motility and increases DNA damage.
No single one of these lines of evidence is conclusive in isolation. Together, they form a coherent and increasingly well-supported hypothesis: that prolonged, direct-contact wear of polyester fabric — particularly against reproductive organs — adds to the cumulative burden of environmental exposures that may impair fertility.
What This Means in Practice
The practical implications follow straightforwardly from the evidence, without requiring anyone to panic or overhaul their entire wardrobe.
If you are actively trying to conceive, or if you are concerned about reproductive health more broadly, the lowest-effort modification available is switching the garments that sit in direct, sustained contact with your reproductive organs — underwear, base layers, activewear liners — from synthetic fabrics to natural fibers. Cotton is the most accessible alternative. Merino wool offers superior thermoregulation, moisture management, and odor resistance without introducing plastic-derived compounds. Linen and hemp are also sound options.
This is not about chasing zero risk. It is about reducing an avoidable exposure in the context of a growing body of research suggesting it matters. The same reasoning applies to choosing BPA-free water bottles or limiting processed food intake: you control what you can, and you move on.
The science is not finished. More and larger studies are needed. Independent replication of the Shafik findings is long overdue. Dose-response data on fabric-derived chemical migration through skin would substantially clarify the risk picture. Longitudinal studies tracking fabric choices alongside fertility outcomes would move the field from plausible hypothesis to established clinical guidance.
Until then, the peer-reviewed research published to date gives reasonable grounds for choosing natural fibers.
Sources cited in this review:
- Shafik, A. (1992). Contraceptive efficacy of polyester-induced azoospermia in normal men. Contraception, 45(5), 439–451.
- Shafik, A. (1993). Effect of different types of textile fabric on spermatogenesis: An experimental study. Urological Research, 21(5), 367–370.
- Shafik, A. (1993). Effect of different types of textile fabric on spermatogenesis: II. Electrostatic potentials generated on surface of human scrotum by wearing different types of fabric. European Urology.
- Mínguez-Alarcón, L., Gaskins, A.J., Chiu, Y.H., et al. (2018). Type of underwear worn and markers of testicular function among men attending a fertility center. Human Reproduction, 33(9), 1749–1756.
- Levine, H., Jørgensen, N., Martino-Andrade, A., et al. (2022). Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries. Human Reproduction Update, 29(2), 157–176.
- Hu, C., Garcia, M.A., Nihart, A., et al. (2024). Microplastic presence in dog and human testis and its potential association with sperm count and weights of testis and epididymis. Toxicological Sciences, 200(2), 235–240.
- Zhang, C., Zhang, G., Sun, K., et al. (2024). Association of mixed exposure to microplastics with sperm dysfunction: a multi-site study in China. eBioMedicine, 108, 105369.
- Guo, Y., Rong, M., Fan, Y., et al. (2025). The presence of microplastics in human semen and their associations with semen quality. Toxics, 13(7), 566.
- Skinner, M.K., et al. (2013). Plastics derived endocrine disruptors (BPA, DEHP and DBP) induce epigenetic transgenerational inheritance of obesity, reproductive disease and sperm epimutations. PLOS ONE, 8(1), e55387.