Men who reported wearing boxers had 25 percent higher sperm concentration than men who wore tighter underwear in a 2018 study of 656 men at a fertility center. The research team adjusted for age, body mass index, smoking, and other confounders, and the gap held. Total count was 17 percent higher in the boxer group too.
That points to heat, not brand. Men's underwear spent 150 years chasing support, shape, and social acceptability while ignoring a biological fact documented for over a century. Sperm production needs the testicles a few degrees cooler than core body temperature. Most underwear on the market was never designed with that in mind.
A century of designing against biology
Before the 1870s, men wore loose linen drawers. No elastic, no pouches. The fabric hung away from the body instead of wrapping the scrotum. It was thermally neutral by accident.
Then Charles Bennett, a bicycle messenger in Boston, got tired of cobblestones jostling his testicles. In 1874 he invented the jockstrap. A pouch with straps held everything in place. It solved a mechanical problem. Sperm never entered the conversation.
In 1935 Arthur Kneibler of Cooper's Inc. introduced the brief, modeled on a swimsuit pattern. He called it the Jockey. The design pulled the scrotum snug against the body. The marketing sold support, neatness, and masculine discipline. Nobody measured scrotal temperature.
The boxer brief came later. It combined the tightness of a brief with the leg coverage of a boxer. The goal was stopping chafing and looking better in the mirror. Thermoregulation was still not on the table.
This was not a conspiracy. Designers simply never thought about sperm biology. The biology sat in journals.
What sperm production actually needs
Sperm production needs temperatures roughly two to four degrees Celsius below core body temperature. That is why the testicles hang outside the body in the first place (Durairajanayagam et al., Reproductive BioMedicine Online, 2015). The cremaster muscle pulls them closer in the cold and lowers them in the heat. The body runs an active cooling system until outside heat overrides it.
When the heat overrides it, sperm parameters suffer. Sauna-level heat temporarily lowers sperm count and can worsen morphology (Garolla et al., Human Reproduction, 2013). The effect is reversible once heat stops (Shefi et al., Fertility and Sterility, 2007). Recovery takes weeks, not days. One full spermatogenesis cycle runs about 74 days, so a hot stretch can show up in a semen analysis weeks later.
What the measurements show
The evidence on underwear and scrotal temperature is consistent. Jung et al. (Human Reproduction, 2005) measured scrotal temperature directly. Men in tight-fitting underwear ran warmer than men in loose-fitting underwear. Sitting raised temperature too. Mieusset et al. (Journal of Andrology, 2007) added more measurements with the same pattern. Sheynkin et al. (Human Reproduction, 2005) found a laptop on the lap raised scrotal temperature enough to matter for men trying to conceive.
Then in 2018 a fertility-center study linked fit to actual sperm parameters. Minguez-Alarcon et al. measured sperm concentration and total count in 656 men and compared the numbers to reported underwear choices. Men who reported wearing boxers had 25 percent higher sperm concentration and 17 percent higher total count than men in tighter underwear.
That is one cohort at one fertility center. It is not a randomized trial. It lines up with the mechanism, which gives it weight.
Why boxers are not the whole answer
Most articles settle into one of two camps. They treat boxers as a closed case, or they push a product. The boxers-as-closed-case position has a problem. Loose cotton boxers breathe better than tight polyester briefs, but cotton also absorbs sweat and holds it against the skin (Jhanji et al., Fashion and Textiles, 2015). Sit at a desk in cotton boxers on a hot day and you have a damp, warm layer against one of the most permeable areas of skin on the body (Maibach et al., Archives of Environmental Health, 1971).
Scrotal skin absorbs more readily than most skin on the body. What sits against that skin all day is worth thinking about.
The product-push position skips the mechanism. No randomized trial has shown that a specific brand improves sperm health. The research points to fit and heat. A brief with a roomy, vented gusset and a wicking fabric creates a different physical environment than a skin-tight polyester brief pulled up against the abdomen. The difference is airflow and temperature, not marketing.
Fabric and the daily heat load
Heat is cumulative across the day. Scrotal temperature rises when a man sits for hours, works with a laptop on his lap, wears tight underwear, or takes a hot bath or sauna (Sheynkin et al., 2005, Jung et al., 2005, Mieusset et al., 2007). An underwear choice worn for eight hours matters more than one worn for eight minutes in the gym.
Fabric matters because damp skin stays warmer. Wicking cellulosic fibers like modal and lyocell move sweat and breathe well in controlled tests (Ozdemir, Journal of Engineered Fibers and Fabrics, 2017, Kucukali-Ozturk et al., Fibers and Polymers, 2023). Cotton holds water. Polyester wicks but is a plastic fiber. Trace antimony from polyester manufacturing can migrate into sweat (Regulatory Toxicology and Pharmacology, 2021), and polyester sheds microfibers during ordinary wear (De Falco et al., Environmental Science and Technology, 2020). Whether that plastic chemistry lowers sperm parameters has not been established. A plastic fiber also does not breathe like a regenerated cellulose fiber.
Three levers worth pulling
If the goal is keeping the testicles closer to the temperature they evolved for, the research points to three adjustable factors.
- Fit. A 2026 narrative review ties garment fit, scrotal thermoregulation, and fertility outcomes together (Zleczewski et al., Translational Andrology and Urology, 2026). Looser fit corresponds to lower scrotal temperature across studies. A relaxed waistband and a gusset with extra room let air move instead of trapping heat.
- Fabric. Breathable, moisture-wicking fabric beats damp cotton and warm plastic in the heat. The physical claim is about airflow and temperature. Anyone selling a fertility guarantee in boxer briefs is selling a story the science does not support.
- Daily heat sources. Laptops on laps raise scrotal temperature. Long sitting does too. A man who sits eight hours a day in warm, tight underwear runs a hotter scrotal environment than a man who moves around in breathable fabric.
During deliberate heat exposure like a sauna session, a cold pack over the groin keeps the testicles cooler in the moment. That is physical cooling during heat exposure. Men who sauna regularly and are trying to conceive may want to think about this one directly. Sperm parameters recover after heat stops, but recovery takes weeks, not days (Shefi et al., Fertility and Sterility, 2007). Stopping the heat before focusing on anything else is cheap and immediate.
A cooler pair without the fertility promises
That is the design logic behind a boxer brief like the Oakman one. A relaxed fit, a gusset built for extra airflow, and a TENCEL MicroModal fabric that moves moisture instead of holding it. The product claims stop at physical comfort and cooling. It never crosses into promising better sperm. If a man wants to reduce the heat he carries around all day, that starts with fit and fabric, not with a supplement stack.
A friend who is trying to conceive usually asks about supplements or timing. Most of the time nobody has asked him about his underwear. I walk him through the heat picture instead. Take stock of daily heat: laptop on lap, long sitting stretches, tight underwear, hot baths, sauna frequency. Then look at fit. Does the underwear hold the testicles snug against the body, or give them room to sit and breathe? Then look at fabric. Does it wick sweat or hold it? Is it a plastic fiber sitting against one of the most permeable areas of skin?
If a man is actively trying to conceive, a doctor who orders a semen analysis will give more specific information than any article can. The broader context matters too. Sperm counts globally have declined roughly 50 percent over the past five decades (Levine et al., Human Reproduction Update, 2023). The causes are debated. Endocrine disruptors, plastics, lifestyle shifts, and later fatherhood all get named. Underwear heat is one modifiable input among several, and it is the one a man can change this afternoon.
The research points to a mechanism, and the mechanism is heat. The practical answer is a cooler, drier, less constricted environment. The underwear industry spent 150 years chasing support. Sperm needed cooler air. That is a design choice a man can make tomorrow morning, and it costs nothing to start.
This content is for educational purposes only and is not medical advice. Oakman products are designed for physical comfort and cooling; they make no claims about fertility, sperm quality, or hormone levels. Consult a healthcare professional for personalized advice.
Frequently asked questions
does wearing boxers improve sperm health
Wearing boxers is linked to lower scrotal temperature, and in one fertility-center study men who reported wearing boxers had 25 percent higher sperm concentration than men in tighter underwear. That is an association, not proof. Heat is the key mechanism, and fit is one factor among several.
what temperature do sperm need to stay healthy
Sperm production needs the testicles roughly two to four degrees Celsius below core body temperature. The body handles this by hanging the testicles outside the abdomen. External heat from tight underwear, sitting, or sauna can override that cooling.
does fabric choice affect testicular temperature
Fabric changes moisture and airflow, and damp skin stays warmer. Cotton holds sweat, polyester wicks but is plastic, and modal or lyocell moves sweat while breathing well. Fit and daily heat sources matter more than any single fabric label.
how long does it take for sperm to recover after heat exposure
Sperm parameters recover after heat stops, but recovery takes weeks, not days. One full spermatogenesis cycle runs about 74 days. A hot stretch can show up in a semen analysis weeks later, so stopping heat early is the cheapest move.