Does Underwear Affect Testosterone? The Fertility-Safe Answer You’ve Been Searching For
Written By The Mr. Fertyl Research & Education Team
When it comes to men’s health, topics like hormone levels and fertility are increasingly part of everyday conversations. One surprisingly common question is whether something as simple as your choice of underwear – boxers vs. briefs, tight vs. loose, cotton vs. synthetic – can impact testosterone levels or sperm quality. It might sound a bit odd at first, but considering that male reproductive organs are directly influenced by temperature and environment, it’s a fair question. In this post, we’ll explore the science behind underwear, testicular heat, and fertility. We’ll see what research says about sperm production, address whether underwear affects testosterone, and provide some friendly, actionable tips to keep things cool (in more ways than one). By the end, you’ll understand how underwear habits can play a role in male fertility and hormone health – and why a fertility-safe choice like Mr. Fertyl’s Bamboo Lyocell underwear could be a smart, sustainable move for both your family plans and your comfort.
Underwear, Heat Retention, and Sperm Production
Let’s start with the basics: temperature matters for sperm. Human testicles are located outside the main body cavity for a reason – they need to stay a few degrees cooler than core body temperature for optimal sperm production [1]. In fact, sperm formation is most efficient around 34°C (93°F), a few degrees below normal body temperature [1]. If the testes get too warm, sperm production can slow down or stall. This is why factors that heat up the scrotum, even mildly, have been scrutinized for their impact on male fertility.
Tight underwear has long been suspected of raising testicular temperature by holding the testes closer to the body. The idea is straightforward: snug briefs or boxer-briefs might act like a mini incubator, whereas loose boxers allow more air circulation. Is there truth to this? Some research says yes. For example, a large 2018 study of 656 men found that those who usually wore loose-fitting boxers had significantly higher sperm counts and concentration than men who wore tight underwear [3]. On average, the boxer-wearers had about 25% higher sperm concentration and 33% more motile sperm in an ejaculate compared to men in briefs [3]. That’s a notable difference in semen quality. The same study also observed that men who wore tight underwear had higher levels of follicle-stimulating hormone (FSH) – a hormone the brain uses to kick-start sperm production [3]. Why would that be? The researchers suspect it’s a sign the body was compensating: when testicles were a bit overheated by tight undies, sperm output dropped, so the brain pumped out extra FSH in an effort to boost sperm production [1]. In other words, tight underwear might stress testicular function enough that the body responds hormonally to try to catch up.
Before you toss out every pair of briefs, though, let’s put these findings in perspective. All the men in that study – whether they wore boxers or briefs – still had sperm counts in the normal, healthy range on average [3]. The differences, while significant, were moderate; wearing boxers was associated with better counts, but it didn’t make the difference between fertile and infertile all by itself. In fact, other research has found that underwear choice alone may not drastically impact actual pregnancy rates. A 2016 study of about 500 men, for example, reported no significant difference in the time it took couples to conceive based on whether the man wore boxers or briefs [3]. And clinicians often note that sperm counts can fluctuate a lot due to various factors, week to week [3]. So, while tight underwear can nudge sperm count downward a bit, it’s usually not the sole cause of fertility problems. It’s one piece of a bigger puzzle.
What about heat retention specifically? Do briefs actually make you warmer down there? Studies that have directly measured scrotal temperature did find some differences, but perhaps smaller than you’d think. In one set of measurements, men wearing tight-fitting underwear had an average scrotal temperature around 35.8°C (96.4°F), whereas boxer wearers averaged about 35.5°C, and men going commando (no underwear) averaged ~35.2°C [11]. That’s only a difference of about 0.3–0.6°C between boxers and briefs. Tiny as it sounds, even slight chronic increases in temperature can impair sperm production over time [1][7]. Remember, sperm are sensitive cells. Anything that interferes with the body’s natural cooling system – whether it’s tight underwear, sitting for too long, a fever, or a hot tub – can have a mild adverse effect on sperm count and quality. In fact, experts often counsel men trying to conceive to avoid unnecessary heat: wear looser pants and underwear, take it easy on long hot baths, and be mindful of habits like placing a laptop directly on your lap [1][4].
To sum up this part: Yes, underwear choice can affect sperm production, mainly via heat. Tight, non-breathable undies can lead to warmer testicles and slightly lower sperm counts [1][3]. Looser, cooler options help sperm thrive. But the impact is usually moderate – switching from briefs to boxers might give your swimmers a boost, though it’s not a guaranteed fertility fix if other factors are at play. Think of it as removing a potential obstacle to let your body do its thing.
Your Fertility Deserves Better Than Synthetics
Shop Fertility-Safe BambooUnderwear and Testosterone: Is Your Hormone Level at Risk?
Now to the crux of the question many men ask: Does underwear affect testosterone levels? Testosterone is the primary male sex hormone, crucial for things like muscle mass, energy, libido, and yes, sperm production. Since testosterone is produced in the testes, it’s reasonable to wonder if overheating the boys with tight underwear could lower your T levels.
The reassuring news is that there’s no strong evidence that typical underwear choices significantly alter testosterone in healthy men. The studies on boxers vs. briefs have mainly measured sperm parameters and reproductive hormones like FSH and inhibin, not testosterone – and they didn’t report any dramatic differences in testosterone between underwear groups [1]. In the dog experiment (an unusual but telling study) where animals wore loosely-fitted cotton or polyester underpants for two years, researchers tracked several hormones including testosterone and found no significant change in testosterone levels for either group [6]. This was despite the fact that the polyester-wearing dogs showed a clear drop in sperm production over time [6]. So, at least in that scenario, sperm count suffered but hormone levels stayed fairly steady.
That said, extreme heat can impact testosterone if it’s severe enough. The key difference is degree and duration. Regular underwear might raise scrotal temperature by half a degree, but consider a more intense situation: One animal study in bulls artificially raised testicular temperature by ~3°C for 48 hours – and it resulted in a sharp drop (up to 90% less) in testosterone production until things cooled down [9]. Similarly, research in rodents and other animals shows that prolonged testicular heat stress can impair Leydig cells (the testosterone factories in the testes) [12]. In humans, a high fever or spending hours in very hot water could temporarily lower sperm and possibly testosterone output. However, your everyday underwear is not going to roast your testes to that extreme level – not even close! So, while the biology tells us “keep the testes cool for best function,” you shouldn’t worry that your favorite pair of briefs is secretly tanking your testosterone. For most men, factors like overall diet, exercise, sleep, and age play a much bigger role in testosterone levels than whether today’s underwear is a little snug or a little loose.
In short, underwear affects fertility more than it affects testosterone. You’re not likely to see a measurable drop in T just from swapping boxers for briefs. But since sperm health is a sensitive indicator of testicular health (and fertility is often the priority for those asking this question), it makes sense to choose underwear that supports your reproductive organs rather than potentially hindering them. Think of it this way: healthy, comfortable testes are good for both sperm production and optimal hormone function. So you can focus on keeping things cool and comfortable down below, knowing that you’re doing a favor for your fertility without worrying about sabotaging your manly hormones.
The Problem with Tight and Synthetic: Breathing Room Matters
Aside from heat, another aspect to consider is tightness and material. Underwear that is too tight (to the point of leaving deep marks on your skin) isn’t great for circulation or skin health. Constant pressure and friction can cause irritation – and as one health review noted, extremely tight garments can even affect how often you use the bathroom, which isn’t ideal for urological health [8]. While snug support has its place (during sports, for example), day-in and day-out compression is not necessary for most men and may do more harm than good. Moderation is key: your underwear should be secure but not squeezing. If you peel off your briefs and see red imprints on your groin or waist, that’s a sign to loosen up a bit on the fit.
Fabric choice also plays a role in the micro-environment of your groin. Modern underwear comes in all kinds of materials – from classic cotton, to polyester blends, to new fabrics like modal, micromodal, and bamboo-derived fibers. The material can influence breathability and moisture control. Synthetic fabrics (like polyester & nylon blends) tend to trap heat and moisture more than natural fibers. They’re often less breathable, which means sweat and warmth accumulate more. A sweaty, warm environment is not only a potential issue for sperm, but can encourage bacterial or fungal growth (jock itch or yeast infections) and just general discomfort. In females, tight non-breathable underwear has been associated with higher risk of yeast infections [8], and while men have different anatomy, the principle of “airflow is healthy” still applies.
Interestingly, there’s some quirky science history regarding polyester underwear and fertility. Back in the 1970s and 1980s, researchers explored whether the rise of synthetic fabrics could be affecting male fertility. A notable experiment had men wear polyester-lined underpants and claimed to find reduced libido and sperm counts, hypothesizing that static electricity from polyester might be to blame. A later controlled study in dogs (mentioned earlier) found that dogs wearing loose polyester underpants for 24 months had a significant drop in sperm count and motility, while dogs in cotton underpants or no underpants were fine [6]. The polyester group’s testes even showed some reversible tissue changes [6]. The researchers speculated that electrostatic charges generated by polyester fabric could impair testicular function [6]. Now, dogs aren’t humans, and this isn’t to say your poly-blend boxer briefs are a fertility hazard – but it’s a fascinating hint that natural vs. synthetic fabrics can have biological effects beyond just temperature. At minimum, it reinforces the benefit of breathable, low-static materials.
On the flip side, natural fibers like cotton – and newer eco-friendly materials like Bamboo Lyocell – allow more airflow and usually wick moisture better. If you’ve ever noticed how a cotton T-shirt “breathes” more than a polyester one, the same goes for your underwear. Drier, cooler skin is healthier skin, and a cooler testicular environment supports better sperm parameters. The goal is to prevent overheating and excessive humidity in the groin region. That’s why material matters: a pair of tight-fitting polyester compression shorts is basically the opposite of what a fertility-conscious guy might want to wear all day.
Fertility-Safe Underwear and Lifestyle Tips
The great news is that you can make simple changes to support your fertility – and none of them are overly burdensome. Here are some actionable, fertility-safe tips regarding underwear and related lifestyle habits:
- Give your guys some air: Whenever practical, opt for looser-fitting underwear (e.g. boxers or relaxed boxer briefs) to allow airflow. You don’t have to ditch briefs entirely, but consider rotating in boxers especially during times you’re trying to conceive. Even at night, some men choose to sleep in loose boxers or nothing at all to keep cool. These small changes can lower scrotal temperature a bit and potentially improve sperm production [1].
- Choose breathable fabrics: Select underwear made from natural, breathable materials. Cotton is the old standby – it’s decent at absorbing moisture and allowing airflow. Bamboo Lyocell, an up-and-coming sustainable fabric, is another excellent choice known for its softness, breathability, and moisture-wicking ability. These fabrics help keep the groin dry and at a comfortable temperature. Avoid wearing non-breathable, thick synthetic underwear for prolonged periods, especially in hot weather or during exercise, as it can trap heat. If you do wear synthetics for workouts (for stretch and support), make sure to change out of sweaty gear soon after.
- Avoid prolonged heat exposure: This one goes beyond underwear. Consistent evidence shows that exposing the testes to high heat can impair sperm. Hot tubs and saunas are common culprits – sitting in very warm water raises testicular temperature to levels that can significantly reduce sperm count for months [4][5]. Limit hot tub soaks when you’re trying for a baby. Similarly, be cautious with laptops on your lap – laptops emit heat and can warm the groin if used that way for long periods [4]. Use a desk or lap pad to shield yourself. Even prolonged sitting (like long drives or desk jobs) can lead to a hot, compressed groin; so take breaks, stand up, and adjust clothing for comfort when you can [1].
- Mind your overall health: Your underwear is one piece of the fertility puzzle, but don’t forget the big picture. Lifestyle factors like maintaining a healthy weight, not smoking, managing stress, exercising regularly, and eating a balanced diet all strongly influence hormone levels and fertility. Obesity, for example, can increase groin fat and insulation, leading to higher scrotal temperatures and altered hormones [7]. So a holistic approach to health will amplify any positive steps you take with your underwear choice. Think of switching to looser, cooler underwear as one easy win alongside other healthy habits.
- Stay consistent and patient: If you do make a change – say you swap to only boxers and cooler fabrics – don’t expect an overnight miracle in your sperm count or testosterone number. Sperm take about two to three months to develop, so improvements in your environment may reflect in semen quality only after a couple of months [5]. Stick with good habits and give it time. The male body is always producing new sperm, so it’s never too late to benefit from healthier choices.
By following these tips, you create a more fertility-friendly environment for your reproductive organs. You’re basically making it as easy as possible for your body to do its job in the baby-making department. And importantly, none of these changes will hurt your hormone health – if anything, they support it.
Stop Trapping Heat Down There
Explore Mr. Fertyl BambooMr. Fertyl’s Bamboo Underwear: A Healthy & Sustainable Choice
As you consider upgrading your underwear drawer with fertility in mind, it’s worth looking at options that check all the boxes: comfortable fit, breathable fabric, and even a positive environmental impact. Mr. Fertyl’s Bamboo Lyocell underwear is a prime example of a health-conscious choice that aligns with these goals. Bamboo Lyocell is a fabric made from organic bamboo pulp through a non-toxic process, resulting in an exceptionally smooth and breathable material. It’s naturally moisture-wicking and thermo-regulating – meaning it helps keep you cool when it’s hot and comfortably warm when it’s cool. This kind of fabric avoids the heat-trapping problem of synthetics by allowing air circulation and pulling moisture (sweat) away from your skin quickly. The result? A drier, cooler environment for your groin, which as we’ve discussed is exactly what you want for optimal fertility and comfort.
From a fertility perspective, Mr. Fertyl’s bamboo underwear offers gentle support without excessive tightness, and the fabric itself won’t contribute to overheating. You can go about your day knowing your choice of underwear is actually working with your body’s needs, not against them. Plus, the softness of Bamboo Lyocell is a nice bonus – no one complains about underwear that feels great to wear!
What makes this option even more appealing is the sustainability factor. Bamboo is a highly renewable resource, and the Lyocell production process is eco-friendly (often recycling water and using environmentally safe solvents). By choosing bamboo underwear, you’re not just doing something good for your own health, but also making an eco-conscious decision. It’s a win-win: support your reproductive health while supporting the planet. In a time when many of us are looking to reduce our environmental footprint, swapping out synthetic or conventional cotton underwear for Bamboo Lyocell is a small change that can make a difference. It normalizes the idea that caring for your fertility and caring for the environment can go hand-in-hand – which is a core part of Mr. Fertyl’s mission. The company aims to make male fertility a comfortable, approachable topic and to provide products that help men lead healthier lives (for themselves, their future families, and the Earth).
Without singling out any competitors, it’s clear that not all underwear is created equal. When you’re comparing options, consider what they’re made of and how they’re made. Mr. Fertyl’s focus on natural fabric and sustainable production means you don’t have to compromise between quality and conscience. You get an underwear that feels good, promotes better airflow (hence likely better sperm health), and avoids the pitfalls we talked about (excess heat, moisture, and synthetic annoyances). For men worried about fertility or those who just value their reproductive health, it’s a smart choice that aligns with the latest understanding of male fertility wellness.
The Bottom Line
So, does underwear affect testosterone? In general, your underwear is not a major driver of testosterone levels – so you can breathe easy that your favorite pair isn’t sabotaging your manhood. However, underwear can affect something equally important: fertility. The style, fit, and fabric of your undergarments influence the temperature and comfort of your testicles, which in turn impacts sperm production. Science shows that wearing tight, non-breathable underwear can lead to slightly lower sperm counts and potentially subtle shifts in reproductive hormones [1][3]. On the flip side, cooler conditions (think loose boxers and breathable fabrics) are associated with better sperm output [3][8]. If you’re planning for a family – or even if you just want to optimize your reproductive health – it makes sense to err on the side of comfort and coolness down below.
The fertility-safe answer is simple: give your swimmers the best environment you can. That means no unnecessary heat or squashing – and yes, your choice of underwear is part of that equation. By choosing options like Mr. Fertyl’s Bamboo Lyocell underwear, you’re taking a positive step to support your fertility without any downside to your testosterone or overall health. In fact, you’re likely to feel more comfortable, and knowing you’re wearing something that’s good for you (and eco-friendly to boot) can be a nice confidence boost. Male fertility and environmental health don’t have to be awkward or niche topics; they’re just another aspect of wellbeing, as normal as eating healthy or getting exercise. With a few mindful choices – and maybe an underwear drawer refresh – you can take care of your future family plans and the planet, one pair of underwear at a time.
- Sharpe, 2018, Expert reaction to study looking at men’s underwear type and semen quality, Science Media Centre. Source.
- Mínguez-Alarcón et al., 2018, Type of Underwear Worn and Markers of Testicular Function Among Men Attending a Fertility Center, Human Reproduction, 33(9): 1749-1755. Source.
- Rettner, 2018, Are Tighty-Whities Bad for a Man's Sperm Count?, Live Science. Source.
- Vij (Cleveland Clinic), 2019, Are You Unknowingly Lowering Your Sperm Count? When to Worry, Cleveland Clinic – Health Essentials. Source.
- Ogle, 2019, Boxers or briefs? 4 common fertility myths debunked, Mayo Clinic Health System. Source.
- Shafik, 1993, Effect of different types of textile fabric on spermatogenesis: an experimental study, Urological Research, 21(5):367-370. Source.
- StatPearls [Zini & Agarwal], 2021, Male Infertility, NCBI Bookshelf (NIH). Source.
- Gallagher, 2020, Should I Wear Tight Underwear? (Healthline, medically reviewed by D. Wilson, PhD). Source.
- Rizzoto et al., 2020, Testicular hyperthermia reduces testosterone concentrations and alters gene expression in testes of Nelore bulls, Theriogenology, 152:64-68. Source.
- ScienceDaily, 2018, Largest study yet shows type of underwear is linked to men’s semen quality (Press release, Harvard T.H. Chan School of Public Health). Source.
- 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.
- Cai, H., Qin, D., & Peng, S. (2021). Responses and coping methods of different testicular cell types to heat stress: Overview and perspectives. Bioscience Reports, 41(6), BSR20210443. Source.
