Yoga Pants and the Mystery of Disappearing Fertility Worldwide

Written by Sayer Ji on August 28, 2025. Posted in Current News

Nobel Prize-winning research reveals how the global shift to synthetic fabrics parallels collapsing sperm counts and rising infertility—affecting both men and women across continents.

The young couple had tried everything. Timing, temperature tracking, dietary changes—nothing worked. After months of frustration, they found themselves in a fertility clinic, answering the usual questions about health and lifestyle. Then came an unexpected question: “What kind of underwear do you wear?”

It sounds absurd—your choice of undergarments affecting your ability to conceive. Yet emerging research suggests that the very fabric touching your most sensitive areas might be acting as an accidental contraceptive. From Nobel Prize-winning scientist Dr. Ahmed Shafik’s experiments rendering men temporarily sterile with polyester underwear to modern discoveries of hormone-disrupting chemicals in yoga pants, the evidence is mounting: synthetic fabrics and fertility don’t mix.

Before you panic and discard your entire wardrobe, know this: the effects appear to be largely reversible. But in an era where one in six couples struggle with infertility¹, understanding how something as simple as fabric choice might tip the scales is worth your attention—especially when emerging research suggests that environmental exposures can cause lasting changes that affect not just you, but potentially your future children.

While Dr. Shafik’s subjects recovered their fertility after removing polyester, we’re now learning that chemical exposures don’t always leave without a trace. Recent groundbreaking research has shown that body cells can transfer genetic information directly to sperm cells—no sexual reproduction required. This means that environmental toxins affecting any part of your body could potentially alter the genetic information in your sperm, passing changes to future generations³². This discovery, published in peer-reviewed journals, reveals that harmful exposures might cause subclinical damage and epigenetic changes that persist even after the initial threat is removed.

The implications are sobering: those polyester underwear might not just temporarily suppress your sperm count—they could potentially be altering genetic information that gets passed to your children. While full fertility might return, the epigenetic legacy of synthetic fabric exposure could linger in ways we’re only beginning to understand. This makes the case for natural fibers even more compelling—it’s not just about your fertility today, but about the genetic health you’re passing forward.

The Nobel Prize-Winning Discovery That Changed Everything

In 1992, Egyptian scientist Dr. Ahmed Shafik published research that should have revolutionized how we think about clothing. His experiment was elegantly simple: he had 14 healthy men wear a polyester “scrotal sling”—essentially a polyester hammock for the testicles—continuously for about 140 days. The results were shocking: every single man became azoospermic, meaning their sperm count dropped to zero².

Their female partners stopped using birth control. For an entire year, not a single pregnancy occurred. The polyester underwear had rendered these men temporarily sterile.

Here’s the remarkable part: approximately five months after removing the polyester slings, the men’s sperm counts returned to normal. The couples who wanted to conceive successfully did so³. The polyester had acted as a completely reversible form of male contraception—no pills, no procedures, just fabric.

What could possibly explain this? Dr. Shafik identified two mechanisms. First, the polyester generated significant static electricity—up to 700 volts of electrostatic potential on the scrotum⁴. This electrical field, he believed, interfered with sperm production. Second, polyester’s poor breathability raised testicular temperature by trapping heat. Sperm production requires the testicles to stay slightly cooler than body temperature (which explains their external position), and wrapping them in synthetic material disrupted this crucial cooling.

Dr. Shafik’s groundbreaking work didn’t stop there. In research that earned him a posthumous Ig Nobel Prize—awarded for studies that “first make you laugh, then make you think”—he dressed 75 rats in tiny custom-made pants. Some wore polyester, others cotton, wool, or polyester-cotton blends⁵.

The results were striking: Rats in polyester pants became significantly less sexually active, attempting fewer matings. The polyester-wearing rats showed the highest static charges on their genital area. When the pants were removed, their libidos returned to normal.

His experiments with dogs revealed even more concerning effects. Female dogs wearing polyester underwear for extended periods showed dramatically suppressed progesterone levels and failed to conceive when mated⁶. Male dogs in polyester developed lower sperm counts, increased abnormal sperm, and signs of testicular degeneration⁷. Most effects reversed after removing the polyester, though some dogs remained subfertile longer.

Shafik’s conclusion was bold: polyester fabric creates an electrostatic field that “traverses” into reproductive organs, disrupting their function⁸. In females, this electrical field inhibited the ovaries. In males, it shut down sperm production.

Critics might argue these were extreme experimental conditions—most people don’t wear the same polyester underwear continuously for months. However, consider modern habits: polyester-blend boxer briefs worn all day, synthetic workout clothes worn for hours, polyester pajamas worn nightly. We might be inadvertently recreating Shafik’s experiments on ourselves.

Your Yoga Pants Are Made of Plastic (And They’re Leaching)

Here’s a fact that might surprise you: 62% of all clothing fibers produced globally are synthetic—essentially plastic spun into thread⁹. That moisture-wicking workout gear is plastic. Those stretchy, comfortable leggings are plastic. That silk-like polyester blouse is definitely plastic

This matters because plastic fabrics don’t remain inert against your skin. They shed microscopic fibers—microplastics—every time they’re worn or washed. Scientists have found these plastic particles everywhere: in human blood, in lung tissue, even in the placentas of pregnant women. One study found microplastic particles in 100% of human placentas tested¹⁰.

The fibers themselves are only part of the problem. The real concern is what’s in them—and what comes out of them when you sweat.

In 2023, environmental groups testing popular athletic wear discovered something alarming: high levels of BPA (bisphenol A) in polyester-spandex clothing. Some sports bras and leggings contained up to 40 times the safe limit of BPA set by California law¹¹. The Center for Environmental Health sent legal notices to multiple major brands after finding these concerning levels¹².

Consider what this means. You put on a sports bra or compression leggings. You exercise, becoming warm and sweaty. Your pores open, your skin becomes more permeable, and you’re essentially marinating in a cocktail of chemicals for hours. As one toxicology expert noted: “Sports bras and athletic shirts are worn for hours at a time, and you are meant to sweat in them, so it is concerning to find such high levels of BPA in them”¹³.

BPA is an endocrine disruptor—it mimics estrogen in your body, binding to hormone receptors and sending confusing signals. In men, higher BPA exposure correlates with lower sperm counts and poorer semen quality¹⁴. In women, those with the highest blood BPA levels show an 83% higher risk of recurrent miscarriage compared to those with the lowest levels¹⁵.

Then there are phthalates—chemicals used to make plastics flexible, found in everything from elastic waistbands to printed logos on shirts. Dubbed “gender-bending” chemicals, phthalates are associated with lowered testosterone in men and reduced sperm count and motility¹⁶. In women, they’re linked to polycystic ovary syndrome and increased miscarriage risk¹⁷.

Perhaps most concerning are PFAS—”forever chemicals” that never break down. Used to make clothing water-resistant and stain-proof, PFAS were detected in 25% of workout leggings and yoga pants tested by environmental groups¹⁸. Women with higher blood levels of PFAS show up to 40% lower chance of getting pregnant within a year¹⁹. These chemicals are so persistent that they’re found in the blood of 99% of Americans tested²⁰.

Can these chemicals actually penetrate your skin? Research confirms they can. Studies show that handling thermal receipt paper for mere seconds delivers BPA into your bloodstream²¹. Dermal exposure to PFAS may carry similar risks as ingestion²². When you’re sweating—which opens pores and creates moisture that helps dissolve chemicals—absorption increases significantly²³.

The Microplastic Invasion

Beyond the chemicals intentionally added to synthetic fabrics, there’s another issue: the plastic particles themselves. Every time you wear or wash synthetic clothing, it sheds tiny plastic fibers. These microplastics are now ubiquitous—in our water, air, food, and bodies, including being found in concerning concentrations in the brain, olfactory bulbs, cardiovascular system, and gut – linked to 4.5x Higher Rates of Heart Attack, Stroke, and Death.

Recent research has labeled microplastics “invisible killers” for female fertility²⁴. In laboratory studies, microplastic exposure decreased the survival of eggs (oocytes) and caused early embryo development problems²⁵. In males, micro- and nanoplastics have been shown to damage sperm cells, reducing their motility and DNA integrity²⁶.

The particles cause both physical and oxidative stress in reproductive tissues. Worse, they act as carriers for other toxic chemicals, delivering a concentrated dose of endocrine disruptors directly to sensitive organs.

One particularly disturbing finding: microplastics accumulate in testicular tissue. A 2024 study found that men with higher levels of microplastics in their testicles had lower sperm counts²⁷. The plastics appeared to be disrupting the blood-testis barrier, a crucial structure that protects developing sperm from toxins.

Why This Matters More Than Ever

Fertility rates are plummeting globally. Sperm counts in Western men have dropped by more than 50% since the 1970s²⁸. One in six couples now struggle with infertility²⁹. While multiple factors contribute to this crisis—diet, stress, environmental toxins—the role of clothing has been largely overlooked.

Consider the timeline: synthetic fabrics exploded in popularity starting in the 1960s and 1970s, roughly paralleling the decline in fertility rates. Today’s young adults—the generation facing the worst fertility crisis in history—have worn synthetic fabrics their entire lives, from polyester baby clothes to synthetic school uniforms to athletic wear as everyday fashion.

The “athleisure” trend has intensified the problem. What was once worn briefly for exercise is now worn all day. Yoga pants at the office, moisture-wicking underwear as daily wear, synthetic fabrics from morning to night. We’re conducting an uncontrolled experiment on our reproductive systems.

The Natural Fiber Solution

The good news: this is one of the easiest environmental health problems to solve. Unlike air pollution or water contamination, you have complete control over what fabrics touch your skin.

Start with underwear—it has the most intimate, constant contact with reproductive organs. Switch to:

• Organic cotton: Breathable, affordable, widely available
• Bamboo (viscose rayon): Naturally antimicrobial, silky soft
• Merino wool: Temperature-regulating, odor-resistant
• Hemp: Durable, becomes softer with washing
• Silk: Luxurious, naturally hypoallergenic

For activewear, the market is evolving. Look for:

• Organic cotton yoga pants
• Merino wool athletic tops
• Tencel/lyocell workout gear
• Brands explicitly labeled “BPA-free” and “PFAS-free”

Shopping tips for safer clothing:

• Check for OEKO-TEX® Standard 100 certification
• Wash new clothes before wearing (removes some chemical residues)
• Avoid anything labeled “wrinkle-free” or “stain-resistant” (likely PFAS-treated)
• Choose untreated, undyed fabrics when possible

If you must wear synthetics:

• Limit exposure time (change immediately after workouts)
• Wear natural fiber underwear as a barrier
• Use a Guppyfriend bag or washing machine filter to catch microplastics
• Choose higher-quality synthetics that shed less

Making the Switch: A Practical Guide

Week 1-2: Underwear Overhaul Begin by replacing your most-worn underwear with organic cotton. You don’t need to discard everything immediately—prioritize what you wear most frequently.

Week 3-4: Sleep Solutions Switch to natural fiber pajamas and sheets. You spend eight hours nightly in these—make them count.

Month 2: Athletic Wear Audit Gradually replace synthetic workout clothes, starting with sports bras and compression shorts—items with the most skin contact.

Month 3: Daily Wear Assessment Evaluate your everyday clothing. Prioritize replacing tight-fitting synthetics like leggings, tights, and undershirts.

Cost-saving strategies:

• Shop end-of-season sales
• Check thrift stores for natural fiber items
• Invest in fewer, higher-quality pieces
• Maintain natural fibers properly to extend their lifespan

The Bigger Picture

Individual action matters, but systemic change is beginning. New York and California banned PFAS in textiles starting in 2025³⁰. The European Union classifies many phthalates and BPA as substances of very high concern³¹. Brands are beginning to respond to consumer demand for safer fabrics.

However, regulation remains slow, and thousands of chemicals remain unregulated. Your best defense is proactive choice: selecting natural fibers whenever possible, especially for intimate apparel and clothing worn during exercise or sleep.

This isn’t about perfection. You don’t need to become an exclusively hemp-wearing purist. But if you’re trying to conceive, dealing with hormonal issues, or simply want to reduce your chemical exposure, your underwear drawer is an excellent place to start.

The Bottom Line

The idea that your underwear could affect your fertility might sound like a conspiracy theory. Yet the science—from Dr. Shafik’s Nobel Prize-winning experiments to modern chemical analyses—points to a real phenomenon. Synthetic fabrics can suppress fertility through multiple mechanisms: static electricity, heat retention, hormone-disrupting chemicals, and microplastic particles.

While the effects appear largely reversible, why continue experimenting on yourself? Natural fibers offer a simple, immediate solution to reduce reproductive stress. Your underwear shouldn’t be birth control—unless you want it to be.

The next time you shop for clothes, remember: cotton loves you back in ways polyester never will. Your hormones—and perhaps your future children—will thank you for making the switch.

Additional Support for Fertility Issues

Over the past twenty years, we have indexed hundreds of studies on both the causes and natural therapeutic interventions for infertility on GreenMedInfo.com. You can consult the following three databases for additional research and support:

• Men’s Inferility Support
• Female Infertility Support
• General Infertility Database

Ready to Take Your Health Further?

Switching fabrics is just the beginning. The synthetic burden on our bodies goes far beyond clothing—from the chemicals in our food to the toxins in our environment. But here’s the empowering truth: your body has an incredible capacity to heal and regenerate when given the right tools.

References

1. World Health Organization. (2023). “1 in 6 people globally affected by infertility.” WHO Report on Global Infertility Rates.
2. Shafik, A. (1992). “Contraceptive efficacy of polyester-induced azoospermia in normal men.” Contraception, 45(5): 439-451.
3. Shafik, A. (1992). “Contraceptive efficacy of polyester-induced azoospermia in normal men.” Contraception, 45(5): 439-451.
4. Shafik, A. (1993). “Effect of different types of textiles on sexual activity.” European Urology, 24(3): 375-380.
5. Kennedy, K. (2017). “One Doctor’s Quest to Reveal the Perils of Polyester Pants.” Atlas Obscura. Retrieved from atlasobscura.com
6. Shafik, A. (2008). “An experimental study on the effect of different types of textiles on conception.” J Obstet Gynaecol, 28(2): 213-216.
7. Shafik, A. (1994). “Effect of different types of underwear on spermatogenesis.” Archives of Andrology, 33(2): 87-92.
8. Shafik, A. (2008). “An experimental study on the effect of different types of textiles on conception.” J Obstet Gynaecol, 28(2): 213-216.
9. Textile Exchange. (2023). “Preferred Fiber & Materials Market Report 2023.”
10. Ragusa, A., et al. (2021). “Plasticenta: First evidence of microplastics in human placenta.” Environment International, 146: 106274.
11. Center for Environmental Health. (2023). “Testing finds high levels of BPA in sports bras and athletic wear.” CEH Report.
12. CBS Los Angeles. (2023). “Your athletic wear could contain high levels of BPA: Here’s a list of brands affected.”
13. Center for Environmental Health. (2023). “Testing finds high levels of BPA in sports bras and athletic wear.” CEH Report.
14. Li, D., et al. (2011). “Urine bisphenol-A level in relation to semen quality.” Fertility and Sterility, 95(2): 625-630.
15. Sugiura-Ogasawara, M., et al. (2005). “Exposure to bisphenol A is associated with recurrent miscarriage.” Human Reproduction, 20(8): 2325-2329.
16. Swan, S.H., et al. (2005). “Decrease in anogenital distance among male infants with prenatal phthalate exposure.” Environmental Health Perspectives, 113(8): 1056-1061.
17. Messerlian, C., et al. (2018). “Urinary phthalate metabolites and ovarian reserve among women seeking infertility care.” Human Reproduction, 33(1): 166-173.
18. Environmental Health News. (2022). “Investigation finds evidence of PFAS in workout and yoga pants.” EHN Report.
19. Carrington, D. (2023). “‘Forever chemicals’ linked to infertility in women, study shows.” The Guardian.
20. Centers for Disease Control and Prevention. (2023). “Fourth National Report on Human Exposure to Environmental Chemicals.”
21. Biedermann, S., et al. (2010). “Transfer of bisphenol A from thermal printer paper to the skin.” Analytical and Bioanalytical Chemistry, 398(1): 571-576.
22. Ragnarsdóttir, O., et al. (2022). “Dermal exposure to PFAS: A review of published literature.” Environmental Research, 209: 112781.
23. Abdallah, M., et al. (2023). “Enhanced dermal absorption of chemicals during physical exercise.” Environmental Science & Technology, 57(12): 4810-4820.
24. Hou, J., et al. (2023). “Toxicity of microplastics and nanoplastics: invisible killers of female fertility and offspring health.” Frontiers in Physiology, 14: 1254886.
25. Liu, Z., et al. (2022). “Polystyrene microplastics induced female reproductive toxicity in mice.” Journal of Hazardous Materials, 424: 127629.
26. Jin, H., et al. (2022). “Polystyrene microplastics induced male reproductive toxicity in mice.” Journal of Hazardous Materials, 401: 123430.
27. Yu, Z., et al. (2024). “Detection and quantification of microplastics in human testicular tissue and semen.” Environmental Pollution, 342: 123089.
28. Levine, H., et al. (2017). “Temporal trends in sperm count: a systematic review and meta-regression analysis.” Human Reproduction Update, 23(6): 646-659.
29. World Health Organization. (2023). “1 in 6 people globally affected by infertility.” WHO Report on Global Infertility Rates.
30. Morgan Lewis. (2024). “New York and California: Bans on PFAS in Textiles and Apparel Begin January 1, 2025.”
31. European Chemicals Agency. (2023). “Substances of very high concern identification.” ECHA Report.
32. GreenMedInfo. (2024). “No Sex Required: Body Cells Transfer Genetic Info Directly To Sperm Cells.” Research compilation showing somatic cell genetic information transfer to germline cells. Retrieved from greenmedinfo.com/blog/no-sex-required-body-cells-transfer-genetic-info-directly-sperm-cells-amazing

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