How Underwear Temperature Affects Sperm Count: What Men Need to Know

Written By The Mr. Fertyl Research & Education Team

It might seem surprising, but the type of underwear a man wears – and how warm it keeps things “down there” – can influence his sperm count and fertility. The testicles are naturally cooler than the rest of the body, typically 2–3°C lower than core temperature (around 34°C or 93°F), because sperm production works best at these slightly lower temperatures [4][5]. Tight, heat-trapping underwear can raise scrotal temperature and potentially impair sperm production. In this post, we’ll explore the science of how underwear temperature affects sperm count and male fertility. Don’t worry – we’ll keep it friendly and straightforward. We’ll also share practical tips on choosing breathable, fertility-friendly underwear (including why Mr. Fertyl’s bamboo underwear might be a game-changer for guys who want to stay cool and boost their reproductive health).

Why Temperature Matters for Sperm Health

Sperm are produced within the testicles in a process that is highly sensitive to temperature. Even a small increase can make a big difference. Research shows that an increase of as little as ~0.7°C in scrotal temperature can significantly reduce sperm counts and even lower a man’s chance of conception [11]. The body has built-in cooling mechanisms – like the cremaster muscles that adjust how close the testes sit to the body – to keep testicles at an optimal temperature for sperm production [5]. When the environment around the scrotum gets too warm, these cooling systems struggle, and spermatogenesis (sperm production) can slow down or become less efficient [5].

Multiple studies underscore the impact of heat on sperm quality. For instance, men exposed to frequent high heat (such as regular sauna users or hot-tub soakers) have shown dramatic drops in sperm count. In one experiment, exposure to sauna heat caused sperm counts to plummet by up to 50% after just a couple of weeks [5]. Another classic study had men wear insulated “heat trapping” support for their testicles; within only 3 weeks, their total sperm counts started decreasing significantly [5]. The good news is these effects are often reversible once the excess heat is removed. A 2007 study reported that among a group of men who stopped using hot tubs (after frequent use), nearly half saw a 491% increase in total motile sperm count just three to six months after quitting the high-heat habit [5]. In short, heat isn’t a friend to male fertility, and keeping the testicles cool is key to maintaining healthy sperm.

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Underwear Choices and Scrotal Temperature

So, how does your choice of underwear come into play? The debate of “boxers vs. briefs” has been around for ages – and science has finally weighed in. Snug-fitting underwear like briefs or tight boxer-briefs tend to hold the testicles closer to the body and often use less breathable fabrics, which can raise scrotal temperature [2]. Looser styles (like classic boxers) allow more airflow and let the testicles hang a bit farther from the body, keeping them cooler. As the Cleveland Clinic bluntly puts it: “Heat isn’t a friend of male fertility. Regular exposure to higher temperatures for your testicles can cause sperm counts to drop. Wearing underwear that keeps things packed tight doesn’t exactly offer a cooling effect.” [1]. In fact, men who wear boxers tend to have higher sperm counts than men who wear briefs, according to multiple studies [1].

A large study published in the journal Human Reproduction (with over 600 male participants) provides some eye-opening numbers. The men who reported usually wearing loose boxer shorts had significantly better sperm metrics than those who wore tight underwear like briefs or jockeys [2]. On average, the boxer-wearers had about 25% higher sperm concentration (sperm per milliliter) and 33% more motile sperm (swimmers) in each ejaculation compared to the tight-underwear group [2]. They also had higher total sperm counts overall [4]. Crucially, these differences remained even after accounting for other factors that affect fertility – such as age, weight (BMI), smoking, hot bath use, and activity level [2].

What about hormonal effects? Interestingly, the same study found that men in tight underwear had higher levels of follicle-stimulating hormone (FSH) [2]. FSH is a hormone the brain uses to signal the testes to produce sperm. Higher FSH in the tight-underwear group suggests that the body was attempting to “compensate” for testicles being a bit too warm and not making quite enough sperm, essentially pushing them to work harder [4]. This provides a biological clue that the heat from snug underwear was indeed affecting testicular function – albeit mildly in most cases.

It’s worth noting that in all groups of that study, average sperm counts were still within the normal range [2]. Wearing briefs daily isn’t likely to sterilize a man outright, and some experts note that a lower sperm count doesn’t always mean infertility if it’s still in a healthy range [2][4]. However, if you’re trying to conceive or just want to maximize your fertility, why not stack the odds in your favor? As Professor Richard Sharpe, a reproductive health expert, advises: switching to looser underwear and avoiding excess heat (like hot tubs and saunas) are easy lifestyle adjustments that “can only be beneficial” for a man’s sperm quality and chances of pregnancy [4]. It’s a simple, no-cost change with no real downside.

Fabric Matters: Breathability and Temperature

Beyond tightness, the material of your underwear also affects heat build-up. Certain synthetic fabrics (like polyester blends found in some sports or compression underwear) can trap heat and moisture. There’s some fascinating (and extreme!) research from the past demonstrating this: One famous study found that men wearing a polyester underwear sling around the clock became completely sperm-free (azoospermic) after several months. The researchers suspected that an electrostatic effect of the polyester plus the lack of breathability disrupted testicular thermoregulation, severely impairing sperm production [10]. (Don’t worry – that effect was reversible when they went back to normal underwear, and nobody is suggesting polyester underwear as real contraception!) The takeaway is that keeping your groin area cool and ventilated is crucial.

Natural fibers like Bamboo Lyocell is much more breathable and tend to maintain a cooler micro-climate for your scrotum. These materials allow air circulation and wick away sweat, preventing the kind of heat and humidity buildup that can bake your boys. Mr. Fertyl’s bamboo underwear, for example, is designed with this principle in mind. Bamboo fabric is not only eco-friendly and super soft, but it’s also excellent at thermoregulation – it lets heat escape and absorbs moisture, helping to keep your testicles at an optimal temperature for sperm production. By choosing underwear made from breathable, natural materials (and in looser fits), you create a cooler environment that your sperm will thank you for. It’s a bit like giving your swimmers an air-conditioned apartment instead of a stuffy closet.

Research-Backed Tips for Keeping Things Cool

Healthy fertility isn’t just about underwear, of course, but every little bit helps. Here are some science-supported tips to keep your reproductive organs cool and your sperm thriving:

  • Choose Loose, Breathable Underwear: As discussed, opt for boxers or boxer-briefs with a roomy pouch, made from bamboo, or other natural fibers. Studies show this can lead to higher sperm counts and motility [2][4]. If you’ve been a lifelong “tighty-whities” guy, consider a switch – some research even observed that when men changed from tight to loose underwear, their sperm quality improved by about 50% within several months [7]. That’s a big gain for such a simple change!

  • Mind the Outerwear Too: Tight jeans or pants, especially if worn together with tight briefs, compound the heat. One study noted that men who wore both tight underwear and tight pants had a substantially higher risk (about 2.5 times) of impaired semen quality, whereas one or the other alone had a smaller effect [7]. So, if you need to wear snug trousers for fashion or work, pairing them with breathable, cooling underwear (like Mr. Fertyl’s bamboo underwear) can mitigate the heat trap.

  • Avoid Prolonged Wet Heat: Hot tubs, Jacuzzis, steam rooms, and long hot baths can all raise scrotal temperature quickly. Consistent exposure can lower sperm counts – and because sperm take ~2-3 months to fully develop, a steep exposure (say a fever or a hot tub binge) might affect your fertility for several weeks afterward [9]. Limiting these activities, or giving yourself a buffer of cooler weeks after intense heat exposure, can help. The recovery study we mentioned earlier showed that quitting the hot tub habit led to remarkable rebounds in sperm counts for many men [5]. In short, think twice about that daily 30-minute soak at 104°F if you’re trying for a baby.

  • Sleep and Relax in Cooler Conditions: Your body temperature naturally drops during sleep, and you can help the process (for both better sleep and sperm health) by wearing loose, light sleepwear – or even sleeping naked. Experts note that “if loose-fitting boxers help that much, imagine what eight hours of no clothing might do” for keeping your testicles cool at night [1]. At the very least, avoid restrictive underwear in bed. Going commando or wearing soft, breathable shorts to sleep can improve air circulation around your groin. This overnight “cool-down” gives your swimmers a welcome break [8].

  • Take Cooling Breaks During the Day: If your lifestyle involves potential heat stress – say you’re an avid cyclist (bike seats can heat up the groin) or you sit for long hours at a desk – try to take short breaks. Stand up, walk around, “air out” a bit. Prolonged sitting can raise scrotal temperature, especially in warm environments or on padded seats [4]. If you have heated car seats, use them sparingly. Little adjustments, like uncrossing your legs or using a laptop on a desk instead of your lap, can prevent additional heat build-up in the genital area [12].

  • Stay Cool Overall: General health and lifestyle affect fertility, too. Keep yourself hydrated and avoid excessive fever when possible (treat fevers promptly, since a high core body temperature can temporarily suppress sperm production [12]). Maintain a healthy weight and manage stress – interestingly, chronic stress can increase core cortisol levels and sometimes body temperature, potentially indirectly affecting reproductive function. A holistic approach to staying cool and healthy will complement the specific steps you take with your clothing.

Mr. Fertyl’s Take – Comfort, Coolness, and Confidence

At first glance, paying attention to your underwear might feel trivial or even a bit awkward to discuss. But male fertility is nothing to be shy about. It’s an important aspect of health, and simple changes can make a positive difference. That’s why Mr. Fertyl has developed its line of bamboo underwear – to give men an option that’s comfortable, eco-conscious, and fertility-friendly. Bamboo fabric offers a silky softness and breathability that rivals the best of fabrics, all while being sustainably produced. By wicking away moisture and allowing air flow, it helps maintain that ideal testicular temperature (~34°C) without sacrificing style or support. In other words, you can take care of your future family jewels and feel good day-to-day, knowing you’re doing something beneficial for your health (and the planet, too).

Throughout this article we’ve highlighted that keeping the scrotum cool = happier sperm. Our bamboo underwear are crafted with this principle in mind – they’re lightweight and cooling, so you won’t get that sweaty, overheated feeling you might with synthetic blends. For men who are planning to conceive or simply want to be proactive about their reproductive well-being, it’s a smart wardrobe upgrade. Plus, even if you’re not actively trying for a baby, cooler and more breathable underwear can improve overall comfort (especially in hot weather or during workouts) and may even benefit testosterone levels indirectly by not subjecting the testes to undue heat stress. It’s a win-win for your health and comfort.

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Conclusion

The temperature of your underwear environment does matter for sperm count and quality. Warmer testes = fewer (and less active) sperm, as decades of research and recent large studies alike have shown. On the flip side, keeping things cooler by choosing the right underwear and habits can help preserve fertility. This doesn’t mean that a pair of briefs will instantly make you infertile – but if you’re looking to optimize your chances of conceiving, or simply to ensure long-term testicular health, it makes sense to favor breathable, loose-fitting undies over tight, heat-trapping ones.

Remember: Men’s reproductive health is a normal and important topic, and taking charge of it can be as easy as opening your dresser drawer. By swapping out tight synthetics for options like Mr. Fertyl’s high-quality bamboo underwear, you’re giving your sperm the comfortable, cool home they deserve. Along with other healthy habits (balanced diet, exercise, not smoking, etc.), this small change can contribute to better fertility outcomes. And even if fatherhood isn’t on your radar right now, your body will still benefit from the improved comfort and airflow.

Talking about sperm count and underwear might have been a taboo or a punchline in the past, but today we know it’s a legitimate health discussion. With a friendly, practical approach, we hope this article makes you feel comfortable taking steps to protect your fertility and normalize conversations about men’s health. So go ahead – give your swimmers some breathing room, stay cool, and take pride in doing what’s best for your reproductive health. Your future self (and perhaps future family) will thank you for it!

  1. Cleveland Clinic. (2022, Feb 16). Is It Healthy To Sleep Naked? Health Essentials. (See “For men: potential fertility boost”). Source.
  2. Rettner, R. (2018, August 8). Are Tighty-Whities Bad for a Man’s Sperm Count? Live Science. (Summary of study in Human Reproduction, 2018). Source.
  3. 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. doi:10.1093/humrep/dey259 (Key study: boxers vs briefs and sperm counts). Source.
  4. Pacey, A. et al. (2018). Expert commentary on underwear and semen quality. Science Media Centre (UK) – Expert Reaction: Men’s Underwear and Sperm Quality. (Summarizing findings of Mínguez-Alarcón et al., 2018). Source.
  5. McGill Office for Science and Society. (2020, Sep 2). Facts and Myths of Male Fertility: Tight Underwear, Hot Tubs, Marijuana, and More. McGill OSS. (Discusses how heat impacts sperm production). Source.
  6. Shefi, S., Tarapore, P. E., Walsh, T. J., Croughan, M., & Turek, P. J. (2007). Wet heat exposure: a potentially reversible cause of low semen quality in infertile men. International Brazilian Journal of Urology, 33(1), 50–57. Source.
  7. Lagacé, M. et al. (2013). Lifestyle factors and reproductive health: Taking control of your fertility. Reproductive Biology and Endocrinology, 11(66). (Includes review of clothing choice on male fertility). Source.
  8. Seattle Sperm Bank. (2018, Sep 1). How Your Choice of Underwear Affects Sperm Production. Seattle Sperm Bank Blog. (Highlights 25% higher sperm concentration and 17% higher total count in loose underwear wearers). Source.
  9. Mayo Clinic Health System. (2019, Mar 1). Boxers or briefs? 4 common fertility myths debunked. Speaking of Health Blog. (Notes that briefs raise scrotal temperature slightly, though direct fertility impact is unproven). Source.
  10. Shafik, A. (1992). Contraceptive efficacy of polyester-induced azoospermia in normal men. Contraception, 45(5), 439–451. (Study on polyester underwear causing reversible azoospermia). Source.
  11. Nikolopoulos, I., Osman, M. W., Haoula, Z., Jayaprakasan, K., & Atiomo, W. (2013). Scrotal cooling and its benefits to male fertility: A systematic review. Journal of Obstetrics and Gynaecology, 33(4), 338–342. Source.
  12. McKinnon, C. J., Joglekar, D. J., Hatch, E. E., Rothman, K. J., Wesselink, A. K., Willis, M. D., Wang, T. R., Mikkelsen, E. M., Eisenberg, M. L., & Wise, L. A. (2022). Male personal heat exposures and fecundability: A preconception cohort study.Andrology, 10(8), 1511–1521. Source.