Does Polyester Lower Sperm Count? The Hidden Risk Lurking in Your Underwear Drawer

Written By The Mr. Fertyl Research & Education Team

The Underwear You Never Thought Twice About

When it comes to male fertility, guys hear a lot about diet, exercise, and avoiding hot tubs. But have you ever stopped to wonder if your underwear could be part of the problem? It sounds almost funny – until you dive into the science. In recent decades, researchers have reported alarming trends: by some estimates, men’s sperm counts worldwide have dropped over 50% in the last 50 years. While many factors are likely involved, experts note that even seemingly minor lifestyle choices – like the type of underwear you wear – can impact your sperm health [7]. In other words, that old pair of polyester briefs in your dresser might be doing more than just providing coverage. It could be contributing to a hidden risk to your reproductive health.

Why Heat Matters for Sperm Health

To understand this risk, we need a quick biology refresher. Sperm are produced in the testicles, which (not by accident) hang outside the body. The reason? Temperature control. Your testicles function optimally a few degrees cooler than your core body temperature [6]. Even a small rise in scrotal temperature – as little as 1°C – can start to interfere with sperm production [6]. Prolonged heat exposure inhibits spermatogenesis (sperm formation), leading to lower sperm counts, less motile sperm, and even DNA damage in the sperm [6]. Essentially, hot balls are unhappy balls (at least as far as fertility is concerned).

Medical experts have hammered this point home. The Mayo Clinic bluntly advises men to “stay cool” down there – keeping the scrotum from getting too warm helps the body make sperm more effectively [1]. This means looser, breathable underwear, taking breaks from long sitting, and skipping the daily sauna or hot tub session [1]. The U.K.’s National Health Service even includes a specific fertility tip: wear loose-fitting underwear because tight undies can raise testicular temperature and potentially harm sperm quality [2]. All this boils down to a simple principle: anything that traps heat around your groin is bad news for sperm.

And it’s not just theory – we have data on underwear choices. A large Harvard study of 656 men found that those who mainly wore boxer shorts had 25% higher sperm concentration and 17% higher total sperm count than men who wore tight briefs [3]. They also had more motile (swimming) sperm and lower levels of FSH (a hormone that ramps up when the body senses it needs to produce more sperm) [3]. The researchers believe the difference came down to – you guessed it – lower scrotal temperatures in the boxer-wearing men. So, it’s pretty clear: keeping things cool and letting your boys breathe is a smart move for fertility.

Polyester: The Hidden Risk in Your Drawer

Now, let’s talk about fabric. You might assume a pair of briefs is a pair of briefs – cotton, polyester, whatever, as long as they’re the same style. But the material your underwear is made from can make a huge difference in breathability and heat retention. Polyester, a synthetic (plastic) fiber, has become hugely popular in clothing for its durability and stretch. However, when it comes to your nether regions, polyester might be an unwelcome guest.

Why? Polyester is far less breathable than natural fabrics. It tends to trap heat and moisture against your skin [8]. Think of wearing a plastic bag versus a cotton T-shirt – the plastic will get sweaty and hot because it doesn’t “breathe.” A textile expert would tell you that polyester’s tight weave and plastic fibers don’t absorb moisture well, which means sweat doesn’t evaporate easily. Instead, heat and humidity build up in that area. For your scrotum, that can lead to chronically higher temperatures, i.e. mild scrotal heat stress [8]. And as we just learned, more heat = fewer happy sperm.

Moreover, some doctors suspect the problems with polyester go beyond just heat. Synthetic fabrics are often treated with chemicals, and polyester itself is derived from petroleum. In one media interview, a physician flat-out called polyester an “endocrine-disrupting” material – suggesting that chemicals in polyester might interfere with hormones like testosterone [8]. He noted that in lab studies, polyester generated electrostatic charges that were linked to significant declines in sperm count [8]. While that sounds a bit sci-fi, the idea is that the static cling you get from polyester (you know, when clothes stick together out of the dryer) might actually impact the cells in the testes over time. The science on the static effect is still emerging, but it’s an intriguing (and slightly unsettling) theory.

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Polyester traps heat. Bamboo lets you breathe.

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Can Polyester Underwear Really Lower Sperm Count?

It might sound like an urban myth – “polyester underwear could make you infertile.” But there are real scientific studies on this, and the results are eye-opening. Perhaps the most dramatic findings come from research by the late Professor Ahmed Shafik in the 1990s. In one experiment, he asked a group of healthy men to wear polyester scrotal supports (basically a sling or pouch made of polyester) 24/7 for a year to see if it could serve as a form of male contraception [4]. The outcome? All of the men became azoospermic – meaning their sperm count dropped to zero – within about 3 to 4 months of continuous polyester wear [4]. Yes, you read that right: polyester underwear completely shut down sperm production in these men, effectively (if temporarily) making them infertile [4]. Fortunately, after the men stopped wearing the polyester sling, their sperm counts recovered over the next few months, confirming the effect was reversible [4]. Still, it’s pretty wild that a mere fabric could have such a powerful impact.

Now, to be fair, that study had the men essentially living in polyester gear non-stop, which is more extreme than your average underwear habits. But it wasn’t just a fluke. Another study by the same researcher looked at dogs wearing polyester vs. cotton underpants (yes, doggie underwear for science!). Over two years, the dogs in polyester had a significant drop in sperm count and motility, plus an increase in abnormal sperm forms, while the cotton-wearing and control dogs stayed normal [5]. The polyester dogs even showed degenerative changes in their testicular tissue under the microscope [5]. When the polyester pants were removed, the dogs’ fertility gradually returned to normal (mostly) – but a couple of them still had lingering low counts. This tells us the effect, while largely reversible, might cause some lasting damage in certain cases.

So what’s going on here? The researchers pointed to two main culprits. First, heat: Polyester likely disrupts the natural cooling of the testicles (“disordered thermoregulation”) when worn constantly [4]. Even if polyester fabric itself doesn’t heat up, it can prevent sweat evaporation and air circulation, so the scrotum can’t cool properly. Second, that weird one we mentioned: electrostatic charges. The friction of polyester against skin can create an electrostatic field across the scrotum [4]. Some scientists theorize this electric field could impair sperm production at a cellular level – perhaps by affecting the delicate cells in the testes or the signals that regulate them [4]. It’s still a hypothesis, but it was significant enough that Professor Shafik literally suggested polyester underwear as a form of “safe, reversible, acceptable and inexpensive” male contraception in his paper [4]. (Note: Don’t try that at home as birth control – it’s not a practical method, and most of us prefer our sperm counts not hitting zero!)

Beyond sperm count, men might experience other downsides from too much polyester. Some have reported increased skin irritation – like rashes or jock itch – because the fabric holds sweat and creates a warm, moist environment (breeding ground for bacteria). In fact, a gynecologist interviewed about polyester underwear noted it “holds in heat and is less breathable,” and warned that sweaty polyester can even release chemicals (like antimony, a component in polyester manufacturing) which may be absorbed by the skin [8]. Antimony is considered a toxic substance and possible carcinogen, so that’s yet another strike against wrapping yourself in plastic-based fabric [8]. To put it bluntly, polyester is basically plastic, and breaking a sweat in plastic underwear isn’t doing your health any favors.

At this point you might be thinking: Alright, so polyester sounds bad… but do I really need to burn all my polyester briefs? The occasional wear (e.g. during a workout if you have sports gear made of polyester blends) is probably fine. The risk comes from long-term, frequent use, especially in ways that keep you hot and bothered. If you and your partner are trying to conceive, or you’re just health-conscious about your swimmers, it’s worth considering a switch in your underwear drawer. As fertility specialists often say, why not control the factors you can? There’s no harm in erring on the side of caution when studies show a “distressing correlation” between polyester underwear and reduced sperm quality and fertility.

A Breathable, Fertility-Friendly Alternative

So, what’s the solution – are we all supposed to go commando or only wear old-school boxers? Not necessarily (though boxers are better than briefs, as we saw). The key is choosing natural, breathable materials for your undergarments. In the same Indian Express piece where doctors blasted polyester, they advised men to opt for natural fabrics like cotton, and specifically noted that polyester is a common underwear material that raises testicular temperature [8]. Natural fibers allow more air circulation and usually absorb moisture, helping sweat to evaporate and cooling the area. Even without reading any studies, you can feel the difference: think of wearing a cotton or bamboo tee on a hot day versus a polyester shirt – the natural fabric is simply more comfortable because it breathes.

One fabric gaining popularity for the eco- and health-conscious is Bamboo Lyocell. This fabric is made from organic bamboo pulp, using a closed-loop process that avoids harsh chemicals. (If that sounds fancy: basically, it’s a textile that comes from bamboo plants but is produced in a cleaner, greener way than traditional “bamboo viscose.”) Bamboo Lyocell is prized for being ultra-breathable, moisture-wicking, and ridiculously soft. It has micro-gaps in the fibers that help pull sweat away from your skin and ventilate heat, keeping you cool and dry even when it’s warm out. In fact, some tests show bamboo-based fabrics can absorb significantly more moisture than cotton, which means less swampiness down south. And unlike polyester, bamboo fabric contains no plastics or toxic additives. You don’t get that clammy, sticky feel – or the chemical exposure – that you might with synthetics.

On top of that, Bamboo Lyocell is a win for sustainability. It’s produced with non-toxic solvents that are recycled in production, making it a cleaner process than standard rayon. Bamboo grows super fast without needing a ton of water or pesticides, so it’s an earth-friendly crop. Plus, the fabric is biodegradable (try composting a polyester brief – it’ll sit for centuries, whereas bamboo will break down). Given how much polyester clothing contributes to microplastic pollution – about 60% of global clothing is now synthetic, and washing these garments sheds half a million tons of microplastic fibers into oceans each year [9] – switching to something like bamboo isn’t just good for you, it’s good for the planet too.

Meet Mr. Fertyl’s Bamboo Underwear – Comfort Meets Peace of Mind

If you’re looking to give your fertility (and comfort) a boost, bamboo underwear is a great place to start. Brands like Mr. Fertyl offer exactly this: high-quality men’s underwear made from Bamboo Lyocell, designed with male reproductive health in mind. Now, this isn’t a hard sell – but it’s worth knowing what’s out there. Mr. Fertyl’s bamboo underwear takes advantage of all the benefits we just discussed. The fabric is buttery soft and breathable, so you won’t feel sweaty during the day. It’s also naturally antimicrobial and odor-resistant (bamboo has some pretty cool properties), meaning your underwear stays fresher and you avoid any funky chemical antimicrobial treatments that some synthetic products use. And because it’s Oeko-Tex certified (i.e. tested for harmful substances), you can be confident there are no nasty chemicals leaching into your skin – a truly non-toxic alternative for your most sensitive areas.

From a comfort standpoint, guys who switch to bamboo often say they can literally feel the difference. No more plasticky waistband chafing or that slight sauna effect you get after hours in polyester. Instead, it’s a breezy, “ahh, that’s nice” feeling – like upgrading from a cramped cubicle to a corner office with AC. Importantly, you’re also doing something proactive for your fertility without any real sacrifice. It’s just swapping underwear – nobody can see it, but you get peace of mind knowing you’re not unknowingly cooking or contaminating your sperm. If you’re already living a healthy lifestyle (eating right, exercising, maybe taking vitamins for male fertility), then addressing your underwear fabric is the next logical step. It’s all about eliminating avoidable risks.

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Hot, Tight, Synthetic?

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Bringing Fertility Talk Out of the Shadows

In closing, let’s normalize this conversation. Talking about sperm count or underwear choices for fertility might feel a bit awkward at first – but it shouldn’t be. Male fertility is a key part of overall health, and it deserves just as much attention as any other wellness topic. If something as simple as switching out polyester underwear for a breathable bamboo pair can help protect your sperm and hormones, why not do it? We routinely consider the safety of what we put in our bodies; this is about being mindful of what we wear on our bodies. By making informed choices (and yes, by supporting brands like Mr. Fertyl that prioritize fertility-friendly design), you’re taking charge of your reproductive health in a smart, sustainable way.

So, the next time you’re getting dressed, give a nod to your future family jewels. Choose fabrics that care for your swimmers rather than sabotage them. Your underwear drawer might just hold a hidden risk – but thankfully, it’s one you can fix. Ditch the heat-trapping polyester, slide into something cool and natural, and let your guys breathe easy. Your sperm (and maybe your future kids) will thank you.

  1. Mayo Clinic – Healthy sperm: Improving your fertility (2025): Emphasizes keeping the scrotum cool; loose underwear and avoiding heat can improve sperm quality. Source.
  2. NHS – Low sperm count (2020): Recommends wearing loose-fitting underwear since tight underwear raises testicular temperature and may affect sperm quality. Source.
  3. Mínguez-Alarcón et al., Human Reproduction (2018): Men who mainly wore boxers had 25% higher sperm concentrations and more motile sperm than men in tight underwear. Source.
  4. Shafik, Contraception (1992): Wearing a polyester sling around the scrotum 24/7 caused men to become azoospermic (zero sperm count) after ~140 days, by raising scrotal temperature and generating static electricity. Source.
  5. Shafik, Urol Res (1993): In dogs, polyester underpants led to a significant decrease in sperm count and motility, plus abnormal sperm, within 24 months; cotton had no effect. Source.
  6. Rajan et al., F&S Reviews (2021): Sperm production requires testicular temperatures 2–4°C cooler than body temp; even a 0.5–1°C rise can impair sperm output and motility. Source.
  7. Scientific American (2023): Notes that lifestyle factors (including type of underwear) influence sperm counts and fertility outcomes. Source.
  8. Bajaj & Srivastav via Indian Express (2023): Doctors report polyester is “less breathable… testicular temperature may rise” with such fabrics, leading to heat stress. They also warn that chemicals in polyester could disrupt hormones and sperm production. Source.
  9. United Nations Environment Programme (2019): Highlights environmental impact – 60% of clothing is synthetic (plastic), and washing polyester releases enormous amounts of microplastic fibers into oceans each year. Source.