Fourteen men and a polyester sling
In the early 1990s an Egyptian surgeon named Ahmed Shafik asked 14 healthy men at Cairo University to do something strange. Each man wore a polyester sling around his scrotum day and night for a full year. Within about 140 days every one of them had no measurable sperm in his semen. Not a low count. Zero.
The study was published in the journal Contraception in 1992 and it has circulated online ever since, usually with the claim that polyester underwear makes men permanently infertile and destroys their testosterone. The real findings are more careful than that. They are also more interesting, because they open a much bigger question about what a life wrapped in plastic is doing to the body.
What the study showed and what it did not
Shafik was not trying to prove that polyester was dangerous. He was testing it as a male contraceptive. The men were aged 32 to 47 and they became sperm-free between 120 and 160 days after first putting on the sling, then stayed that way for the rest of the year. He gave two reasons. The fabric held heat against the testes, which need to sit cooler than the rest of the body. Friction between polyester and skin also built up a static electric charge that he believed interfered with sperm production.
Then the slings came off. Sperm counts climbed back to normal over roughly five months. Five of the couples wanted children afterwards and all five conceived. The effect was total but it was temporary.
The viral version leaves out three things. The paper is about sperm production and it does not support the claim that polyester wipes out testosterone. The men wore a snug sling around the clock for a year, which is far more exposure than a pair of polyester briefs worn during the day. The study also had only 14 men with no comparison group and it has had very little follow-up in the thirty years since. It is best read as a striking early signal.
Larger research does back the heat side of the story. A Harvard study of 656 men published in 2018 found that those who mostly wore loose boxers had a sperm concentration 25 percent higher than men who wore tighter underwear.
Plastic is already inside the body
Fabric is only one route. In 2024 researchers at the University of New Mexico examined 23 human testes and 47 from dogs. They found microplastics in every single one. The human samples averaged about 330 micrograms of plastic per gram of tissue, nearly three times the level found in the dogs. In the dogs, where sperm could still be counted, higher levels of PVC went with lower sperm counts. The human tissue had been preserved so its sperm could not be counted, which means the study shows a link worth taking seriously and stops short of proving cause.
Much of that plastic arrives through the mouth. A Columbia University team reported in 2024 that a single litre of bottled water holds around 240,000 plastic particles. About 90 percent of them were nanoplastics, small enough to pass from the gut into the bloodstream. Synthetic clothing adds to the load as well. Polyester, nylon and acrylic shed tiny fibres every time they are worn or washed and those fibres become part of the household dust people breathe in and swallow.
The chemicals that come with plastic
Plastic is never just plastic. Phthalates are added to make it soft and flexible. Bisphenols such as BPA make it hard and clear. Both can mimic or block the body's own hormones, which is why scientists call them endocrine disruptors. A 2014 analysis of United States national health survey data found that people with higher phthalate levels in their urine tended to have lower testosterone. Heat makes the problem worse. A bottle left in a hot car or a meal microwaved in a plastic container releases far more particles and additives than the same plastic kept cool.
The wider trend is hard to ignore. A 2017 review that pooled 185 studies found that sperm concentration in men from North America, Europe, Australia and New Zealand fell by more than half between 1973 and 2011. Scientists still debate the causes and how reliable the older counts were. Plastics are one suspect among several that include diet, weight, smoking and inactivity.
What men wore before polyester
Polyester fibre was first made in a British laboratory in 1941. Before that every garment a person owned was cotton, linen, wool or silk. Today polyester accounts for more than half of all the fibre produced in the world. People wore natural cloth against the skin for thousands of years. The plastic version has been tested on the human body for about seventy.
Natural fibres breathe. They let heat and moisture escape, which is exactly what the male body is built to do in that part of the anatomy. Loose cotton and linen were the ordinary dress of hot climates long before anyone measured testicular temperature in a laboratory.
Simple ways to cut back
- Check underwear labels. Polyester, nylon, acrylic and elastane are all plastics. Choose cotton, linen or fine wool in a looser fit.
- Sleep in natural fibres or in nothing at all.
- Drink from glass or stainless steel. Filtered tap water carries far less plastic than bottled water.
- Never heat food in plastic. Use glass or ceramic in the microwave.
- Keep plastic bottles and containers out of hot cars and direct sun.
The encouraging part is how much of this sits within reach. The body does not hold on to phthalates and BPA for long. It clears most of them within days, which means every swap lowers the load almost straight away. Going back to natural fibres, taking plastic out of the wardrobe and the kitchen and cutting down on other endocrine disruptors in the home can make a real difference to hormones, fertility and everyday wellbeing. Plastic took over daily life in a single lifetime. Choosing the cloth, glass and metal that served people for thousands of years is one of the simplest ways to give the body back the conditions it was made for.
References
- Shafik A. Contraceptive efficacy of polyester-induced azoospermia in normal men. Contraception, 1992.
- Hu CJ et al. Microplastic presence in dog and human testis and its potential association with sperm count. Toxicological Sciences, 2024.
- Qian N et al. Rapid single-particle chemical imaging of nanoplastics by SRS microscopy. Proceedings of the National Academy of Sciences, 2024.
- Mínguez-Alarcón L et al. Type of underwear worn and markers of testicular function among men attending a fertility center. Human Reproduction, 2018.
- Meeker JD and Ferguson KK. Urinary phthalate metabolites are associated with decreased serum testosterone in men, women and children from NHANES 2011-2012. Journal of Clinical Endocrinology and Metabolism, 2014.
- Levine H et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update, 2017.