Men who reported wearing boxer shorts had 25% higher sperm concentration and 17% higher total sperm count than men who wore tighter underwear in a 2018 study of 656 men at a fertility center (Minguez-Alarcon et al., Human Reproduction). That is not proof that tight underwear caused the difference. The study was observational. But the finding fits a well established mechanism: sperm production needs the testicles a few degrees cooler than core body temperature, and tight clothing pulls them closer to the body and traps heat.
The short answer is yes, with a caveat. Tight clothing can raise scrotal temperature, and sustained heat can suppress sperm production. The effect is usually modest and appears to reverse when the heat source goes away. If you are trying to conceive, clothing choice is one of the few variables you can adjust without spending money or waiting for a prescription.
What the research actually shows
The 2018 study used self reported underwear type from men attending a fertility center. Men who mostly wore boxers had higher sperm concentration, higher total count, and lower follicle stimulating hormone than men who mostly wore briefs, jockey shorts, or other snug styles. The authors adjusted for factors such as age, body mass index, smoking, and time since last ejaculation. The differences were moderate, not massive, and the population was not a random sample of all men.
One limitation is that most studies rely on self reported underwear type rather than direct measurements over time. Another is that men who wear loose underwear may also have other habits that support sperm health, such as being more active or spending less time sitting. The observational design means researchers can adjust for known confounders but cannot rule out all of them.
Two earlier studies measured scrotal temperature directly. Jung et al. (2005, Human Reproduction) fitted men with temperature sensors and found that tighter underwear and sitting raised scrotal temperature compared with looser underwear and movement. Mieusset et al. (2007, Journal of Andrology) reported a similar pattern. The temperature shift was small in absolute terms, often less than one degree Celsius, but sperm production is sensitive enough that small differences can matter over weeks.
The strongest evidence that heat suppresses sperm parameters comes from deliberate heat exposure. Garolla et al. (2013, Human Reproduction) found that sauna-level heat temporarily lowered sperm count and worsened morphology. The effect reversed once heat exposure stopped. Shefi et al. (2007, Fertility and Sterility) found that semen parameters recovered after men stopped wet heat exposure. A 2026 narrative review in Translational Andrology and Urology tied garment fit, scrotal thermoregulation, and fertility outcomes together and described the same pattern (Zleczewski et al., 2026).
Why heat matters more than pressure
The testicles sit outside the body because spermatogenesis needs a temperature roughly 2 to 4 degrees Celsius below core body temperature. The scrotum has a muscle layer, the cremaster, that raises and lowers the testicles to regulate temperature. Tight underwear and tight pants compress the testicles against the groin, reduce air circulation, and interfere with that natural regulation. Developing sperm cells are temperature sensitive. A fever can temporarily lower sperm count for the same reason.
Heat, not pressure, appears to be the main issue. That distinction helps explain why loose pants over tight underwear can still be a problem, while loose underwear under fitted pants may be less of one. The body tolerates brief pressure well. It cannot compensate as easily for sustained heat.
Tight pants or tight underwear: which matters more?
Both can raise scrotal temperature, but underwear sits closer to the skin, so it has a more direct effect. Skinny jeans, compressive athletic tights, and slim trousers add a second layer of insulation. The combination that shows the most consistent advantage in studies is a roomier fit at the crotch, whether that comes from boxers, boxer briefs with a generous pouch, or trousers that do not compress the groin. Fabric breathability helps, but fit is the bigger lever. A tight pair of boxer briefs can trap as much heat as a pair of briefs.
Sitting compounds the problem. Jung et al. found that scrotal temperature rose when men sat down, and tight underwear kept it elevated. A laptop on the lap adds another heat source. Sheynkin et al. (2005, Human Reproduction) found that working with a laptop on the lap raised scrotal temperature. Add tight clothing, a hot laptop, and hours of sitting, and the heat load stacks up.
Does this mean tight clothing causes infertility?
For most men, no. The effect sizes in studies are modest, and sperm counts fluctuate for many reasons. Tight clothing is one environmental factor among several. Men who are not trying to conceive may never notice a difference. Men who are trying to conceive and have borderline sperm parameters may see a meaningful change by switching to looser clothing.
The key point is that heat-related suppression appears reversible. The studies on sauna and wet heat show recovery over weeks to months once heat exposure stops. The practical question is whether you have a reason to care right now, such as a planned pregnancy or a semen analysis that came back low.
How long does it take to see a change?
Sperm production takes roughly 64 to 74 days from start to finish. A semen sample collected today reflects conditions from two to three months ago. If you switch from tight to loose clothing, any improvement may take eight to twelve weeks to show up in a semen analysis. This is why clinicians often retest after three months rather than a few days. The lag also means that a single hot weekend is unlikely to show up immediately. It is the standing pattern, month after month, that matters most.
Practical adjustments
If you are trying to conceive, a looser fit is one low-cost adjustment. You can make a handful of changes without overhauling your wardrobe:
- Look for underwear with enough room that the testicles can sit away from the body.
- Stand up and walk around during the day to let the scrotum cool.
- Keep a laptop on a desk instead of your lap.
- Reduce long hot tub or sauna sessions in the weeks before a semen sample if a doctor has flagged heat as a possible factor.
A doctor can order a semen analysis before and after these changes to see if they matter in your case. That is the only way to know whether tight clothing is contributing to a low count or whether something else deserves attention. If you have a known fertility concern, or if you have been trying to conceive for a year without success, a healthcare professional can help you sort out which factors are relevant.
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.