Tight Underwear and Infertility: The Hidden Connection

Written By The Mr. Fertyl Research & Education Team

Understanding the Heat and Sperm Connection

It’s well-established that human testicles are designed to function a bit cooler than core body temperature. In fact, normal scrotal temperature is a couple of degrees lower than the rest of the body (around 35°C or 95°F) [5]. This lower temperature is crucial for optimal sperm production (spermatogenesis). Even a small rise of just a few degrees can impair sperm creation and potentially cause infertility [5]. The body has natural ways to regulate this (the cremaster muscle moves the testicles closer or further from the body to adjust temperature [5]), but external factors can override these measures.

One key factor is heat buildup from tight clothing. Tight underwear or pants hold the testicles snug against the body, trapping heat. Studies confirm that wearing tight underwear does increase scrotal temperature – typically by about 0.5°C to 1°C [5][9]. That may not sound like much, but remember, the margin for optimal sperm temperature is small. Research has long shown that excess heat harms sperm: for example, men exposed to frequent saunas or hot tubs can experience up to a 50% drop in sperm count [5], and avoiding these heat sources can reverse the effect (one study found that men who stopped using hot baths saw a 491% increase in their total motile sperm count three months later) [5]. In short, heat is the enemy of sperm, and tight underwear can contribute to that heat by preventing the testicles from cooling off.

Myth vs. Evidence: Does Tight Underwear Lower Fertility?

There has been a lot of debate (and confusion) about whether the choice of underwear genuinely affects male fertility. You may have heard the classic question, “Boxers or briefs?” and gotten mixed answers. Let’s separate myth from reality:

  • The Myth/Old Perception: Some sources have claimed that it doesn’t really matter – that while briefs might raise temperature a bit, there’s “no research saying that this affects fertility,” so men should just wear whatever’s comfortable [2]. This view treats the underwear issue as an old wives’ tale. It’s true that simply switching underwear isn’t a magic bullet for male fertility, and earlier studies had inconsistent results. In fact, one large 2016 study found that men who wore tight underwear had slightly higher scrotal temperatures (~1°C higher) and some differences in semen quality, but they did not have significantly lower pregnancy rates with their partners [9]. In other words, the small temperature increase wasn’t enough to clearly delay conception in that study. Moreover, wearing tight undies definitely won’t make you sterile – it doesn’t lower sperm count enough to act as any form of birth control [4].

  • The Evidence: More recent research, however, indicates that underwear choice does have a measurable impact on sperm. Notably, a 2018 study by Harvard scientists looked at men attending a fertility clinic and found significant differences between men who wore boxer shorts versus those who wore tighter underwear. Men who primarily wore boxers had a 25% higher sperm concentration and 17% higher total sperm count compared to men who wore tight underwear [7]. They also had lower levels of follicle-stimulating hormone (FSH) on average, suggesting the body wasn’t having to work as hard to produce sperm [7]. (FSH is a hormone that ramps up when the testicles need extra stimulation – higher FSH in the tight-underwear group implied their bodies were trying to compensate for a heat-related sperm production drop.) Another earlier study in the UK similarly observed that men who “[did] not wear loose underwear” had higher odds of low motile sperm count, linking tight underwear to poorer sperm motility [8]. And broadly, medical experts acknowledge that excess heat is a risk factor for male infertility – whether from hot tubs, laptops on the lap, or snug briefs. The Cleveland Clinic, for example, advises that high heat exposure from things like tight clothing, frequent hot tub use, or heating pads on the groin can impair sperm production [1]. Mayo Clinic’s own guidance for improving sperm health includes a simple tip: “Stay cool.” They note that if the scrotum gets too warm it may reduce sperm production, so wearing loose-fitting underwear and avoiding saunas/hot tubs may improve sperm quality [3].

So, what’s the bottom line from these seemingly mixed messages? Essentially, tight underwear isn’t likely to single-handedly make a fertile man infertile, but it can nudge your sperm count and quality in the wrong direction. For a man with borderline fertility or trying for a baby, every bit counts. Why add unnecessary heat stress to your testicles if you don’t have to? As one urologist quipped, it’s a good idea to “loosen your trousers” if you’re trying to conceive [5]. The jury may still be out on the exact magnitude of the effect, but the consensus is leaning toward this: cooler is better for male fertility.

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How to Keep Things Cool (Without Sacrificing Comfort or Style)

The good news is that this is one fertility risk factor you can actually do something about in your everyday life. Here are some practical, easy tips for choosing fertility-friendly clothing and habits:

  • Opt for Loose or Breathable Underwear: If you’ve been a briefs or tight boxer-briefs guy, consider switching to looser boxers – especially during the day or when you’ll be in warm environments. Even at night, you might try sleeping in loose shorts or no underwear at all to give your groin a breather. One study noted many men naturally switch to cooler options at bedtime [9]. The idea is to prevent constant heat buildup. Tip: If you’re not a fan of traditional boxers because of comfort or support, look for modern designs that balance support with breathability (more on this below).

  • Choose the Right Fabric: The material of your underwear can be just as important as the fit. Synthetic fabrics like polyester or nylon can trap heat and moisture, while natural fabrics allow more airflow. Health experts recommend natural fibers like cotton or bamboo for undergarments, since they absorb moisture and “air out” the area better than synthetics [6]. Bamboo Lyocell fabric, in particular, is earning praise as a super breathable, moisture-wicking option – it’s ultra-soft and helps keep the temperature down in your nether region. (It’s also eco-friendly, which is a nice bonus for the environmentally conscious.) For example, Mr. Fertyl’s Bamboo Lyocell underwear line is specifically designed with this in mind – using fabric that is breathable and thermoregulating to keep your scrotum cool and comfortable. By switching to such fertility-friendly materials, you can stay comfy and give your sperm a better environment.

  • Avoid Long Periods of High Heat Exposure: Tight underwear isn’t the only heat source to watch. Try not to sit with a laptop directly on your lap for extended periods (use a desk or cooling pad, since even with a pad, your closed thighs alone can raise scrotal temp noticeably) [5]. Limit time in hot tubs, saunas, or very hot baths if you’re actively trying to conceive – these can cause a temporary drop in sperm count [5]. The effects of heat are usually reversible as new sperm are generated over ~3 months, but you don’t want to constantly set yourself back. Even at the office or during a long drive, it’s not a bad idea to stand up and cool off for a few minutes periodically if you’ve been seated for hours.

  • Stay Comfortable and Supported: “Loose” doesn’t have to mean baggy old boxers that bunch up uncomfortably. Look for underwear that provides support without squeezing. Many fertility-conscious men are turning to designs like Mr. Fertyl’s Bamboo Lyocell underwear, which use a soft, stretchable natural fabric to give a snug fit that doesn’t overheat. The bamboo-derived fabric breathes much better than traditional cotton, helping to dissipate heat while still offering support and style. In other words, you can have the best of both worlds – support for daily activities and a cooler environment for your boys down under. You shouldn’t have to sacrifice your personal style or comfort for the sake of fertility. With the right underwear, you can do good for your reproductive health and feel good wearing it.

  • Healthy Habits Help: Since we’re on the topic of fertility, remember that other lifestyle factors also play a role. Maintain a healthy weight, avoid smoking, and manage stress – all of these can impact sperm quality. But when it comes to your wardrobe, the guiding principle is simple: keep things cool and not constricted.
Flat lay of non-toxic bamboo men’s underwear in black and beige, fertility-safe and breathable.

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Embracing Fertility-Friendly Choices

Talking about underwear and fertility might feel a bit awkward for some men at first, but it’s actually a simple and empowering way to take control of your reproductive health. There’s no need for shame – after all, fertility is just another aspect of health, and it’s influenced by everyday behaviors. By choosing underwear that keeps your testicles cooler and by avoiding unnecessary heat, you’re creating a better environment for sperm to thrive. It’s a small change with potential big benefits for those looking to start a family.

And thanks to innovations in men’s apparel, this change doesn’t mean resorting to unappealing or uncomfortable options. Brands like Mr. Fertyl are normalizing the conversation around male fertility and offering solutions (like that Bamboo lyocell underwear) so that men can be proactive about their fertility without feeling stigmatized. These products blend into your life – they’re stylish, high-quality, and eco-friendly – so taking care of fertility becomes as routine as picking out what clothes to wear each day.

Bottom line: Tight underwear can contribute to lower sperm count and quality by raising testicular temperature and reducing circulation in the area. It’s not a guaranteed ticket to infertility on its own, but it’s a risk factor you can easily avoid. Swapping those tight briefs for cooler, breathable underwear is an easy, natural step to support your reproductive health. Your future self (and maybe future kids!) will thank you. So don’t sweat it – or rather, let your guys breathe so they don’t have to sweat so much. Staying cool, in every sense of the word, might just be one of the smartest moves for your fertility and overall comfort.

  1. Cleveland Clinic. (n.d.). Infertility: Types, Causes, Symptoms, Diagnosis & Treatment. Source.
  2. Mayo Clinic Health System. (2019, March 1). Boxers or briefs? 4 common fertility myths debunked. Source.
  3. Mayo Clinic. (2025, March 11). Healthy sperm: Improving your fertility. Source.
  4. Nemours KidsHealth. (2022). Can wearing tight clothes affect sperm count? (For Teens). Source.
  5. McVean, A. (2020, September 2). Facts and Myths of Male Fertility: Tight Underwear, Hot Tubs, Marijuana, and More. McGill Office for Science and Society. Source.
  6. Gallagher, G. (2020, October 2). Should I Wear Tight Underwear? Healthline. Source.
  7. Mínguez-Alarcón, L., et al. (2018). Type of underwear worn and markers of testicular function among men attending a fertility center. Human Reproduction, 33(9), 1749-1756. Source.
  8. Povey, A. C., et al. (2012). Modifiable and non-modifiable risk factors for poor semen quality: a case-referent study. Human Reproduction, 27(9), 2799-2806. Source.
  9. Sapra, K. J., et al. (2016). Choice of underwear and male fecundity in a preconception cohort of couples. Andrology, 4(3), 500-508. Source.
  10. CNN (Health). (2018, August 8). Is your underwear helping or hurting your chances of becoming a father? Source.