The Vitality ReviewPeer-Reviewed Men's Health Research
Editorial28 studiesHeat & Temperature

What Heat Does to Your Sperm, and What to Do About It

By Adam Gleason, MD, Founder, OakmanReviewed by The Vitality Review medical editorsLast reviewed September 2026About 6 minutes

The Vitality Review is published by Oakman, which sells cooling underwear. Every study below is independent and linked in full, and nothing here claims that any product treats any condition. How we read studies

A sepia scientific plate of human sperm cells, head, midpiece and tail.

Heat is potent enough that deliberately raising testicular temperature was tested as male contraception [1]. The everyday exposures below are milder than those research protocols, but they act on the same biology [2, 3]. Heat lowers sperm count, sperm movement, and damages the sperm's DNA [4, 5, 6, 7]. Testicular heat typically comes from a hot occupation, regular sauna, and hot tubs and hot baths [8, 7, 9]. Day to day, the biggest driver of scrotal temperature is sitting, and higher scrotal temperature is associated with lower sperm counts [10, 11].

The damage is reversible but it takes time. A full cycle of sperm production takes about 64 days, a little over two months [12]. Some sperm health measures return to normal within three months after heat exposure stops, while others may take closer to six months [13, 4, 7, 14]. Testicles sit outside of the abdomen because sperm production only works in environments a few degrees cooler than the rest of your body [2, 3, 15]. This article discusses what to do about it, why the testicles need to stay cool, and which heat exposures matter.

What to do

Fortunately, there are inexpensive and low effort ways to avoid excessive scrotal heat.

  • If your job puts you in the heat, solve that first if possible [8, 16]. Wear breathable clothing and take breaks to cool off.
  • Break up long stretches of sitting, the biggest everyday driver of scrotal temperature [10].
  • Avoid using a laptop on your lap. If unavoidable, sit with your knees apart [17, 18].
  • Skip sauna, hot tubs, and hot baths while trying to conceive. Give it three to six months after stopping heat exposure before judging a semen test [7, 6, 9], since that is the time it takes for sperm quality to normalize.
  • If you cannot (or prefer not to) remove a heat source while trying to conceive, cooling is a reasonable addition to your routine since it is inexpensive and measurably lowers scrotal temperature [19, 20, 21].
  • Underwear that breathes is another inexpensive and easy modification to reduce daily heat [22, 23].

Why the testicles need to stay cool

The scrotum is exclusive to mammals. It appeared more than 150 million years ago, at about the time early mammals became warm-blooded and their body temperature settled near 98.6 F. Mammals that have since moved the testicles back inside the abdomen, such as whales, either run a cooler body temperature or have a special blood supply that cools the testicle [2].

The leading explanation for the cooler temperature is DNA protection. A cooler testicle means less oxidative damage to DNA (damage from reactive oxygen, the same chemistry that rusts metal) and fewer sperm mutations [2]. A second explanation is storage. Sperm wait for days to weeks in the epididymis (the coiled tube behind each testicle where sperm mature), and the storage end of the epididymis sits in the coolest part of the scrotum, where sperm burn less energy and take less damage while they wait [2].

Heat does its damage to the dividing sperm cells. When the testicle is warmed, the cells in the middle of becoming sperm (spermatocytes and spermatids, the two stages after the stem cells) die off in large numbers, even after short periods of mild heating [2, 3]. Heat also damages the DNA in the mature sperm that survive, which is why DNA damage shows up in the warming belt, water bath, and sauna studies below [3, 4, 6, 7].

What warms the testicles up

To varying degrees, seated work, laptop usage, driving, and tight underwear all increase scrotal temperature. Studies show that seated work is the strongest everyday driver of scrotal temperature. Men who reported more than six hours of sedentary work in a day ran a median scrotal temperature of 94.5 F, about 3 F higher than men who reported under an hour. The same research group found that higher scrotal temperature was associated with lower sperm counts, but found no significant change in sperm quality from prolonged sitting itself [10, 11]. Tight-fitting underwear raises scrotal temperature more than loose underwear or none. Walking lowers scrotal temperature compared with sitting [22].

Figure 1Three degrees is the whole argument
91.6 FSat under an hour
94.5 FSat six hours or more
98.6 FCore body temperature
88919497100
Scrotal skin temperature, median, in 101 men who logged their day and wore a sensor [10]. Core body temperature [2]. Sperm production works a few degrees below the lower end of this scale, not the upper.
WHAT THE STUDIES SHOWsitting, laptops, and drivingSix hours of sedentary work ran 3 F hotter than under an hour. The laptop added another 1 F.5 studiesRead it

In 101 Danish men who logged their day and wore a scrotal temperature sensor, scrotal temperature ran a median 91.6 F in men who sat for under an hour and 94.5 F in men who sat for six hours or more, and sitting explained about a third of the variation across a day [10]. The same research group measured semen quality in 99 healthy men. Sperm concentration fell about 40 percent for every 1.8 F rise in median daytime scrotal temperature, and total sperm count fell with it, while sperm movement and shape did not change. Sitting at work, a strong driver of that temperature, showed only weak and inconsistent links to semen quality on its own [11].

Over one hour of sitting, scrotal temperature rose about 4 F with no laptop and about 5 F with a laptop on the lap, so the laptop added about 1 F on top of the sitting itself [17]. Sitting with knees apart and a lap pad cut the laptop rise to about 2.5 F, against about 4 F with knees together [18].

After two hours of driving, scrotal temperature ran about 3.5 F higher than scrotal temperature had been after 40 minutes of walking [24]. Note that the driving figure was measured against walking, while the laptop figures above are rises over an hour of sitting, so the two are not directly comparable [17, 18, 24].

WHAT THE STUDIES SHOWunderwearIt changed scrotal temperature every time. It changed pregnancy outcomes in no study.2 studiesRead it

Fifty men each did six 45-minute periods, sitting or walking on a treadmill, wearing tight underwear, loose underwear, or none, in random order. Scrotal temperature was highest with tight underwear, lower with loose, and lowest with none, and walking lowered scrotal temperature compared with sitting in every condition [22].

A 2026 review of underwear and fertility found tighter underwear consistently linked to higher scrotal temperature, modest and inconsistent differences in sperm measures between boxers and briefs, and no clear difference in pregnancy outcomes. Its conclusion: underwear choice alone is unlikely to meaningfully change fertility [23]. With that said, breathable underwear is a cheap and risk-free way to reduce daily heat [22].

The job matters more than the weather

If you work in the heat and are able to reduce heat exposure, solve that first. In 485 men at one clinic, occupational heat exposure carried 4.2 times the odds of low semen quality, the strongest risk factor in that study [8]. Read it with the caution its authors give it. Only 25 of those 485 men worked in the heat, which is why the range around 4.2 runs from 1.5 to 11.5.

Ambient weather is a weaker and more contested factor, and the size of the effect is part of why. One study showed a slight loss of sperm motility with higher apparent temperature while another found the fastest sperm in the summer and slower in the winter months of both Denmark and Florida [25, 26]. This indicates that something seasonal is moving sperm quality that outdoor heat does not explain.

WHAT THE STUDIES SHOWheat at work and heat outdoors4.2 times the odds at work, on 25 exposed men. Outdoors, the season beat the temperature.3 studiesRead it

In 485 men at one clinic in China, occupational heat exposure carried 4.2 times the odds of low semen quality, the strongest risk factor the study measured. Twenty five of the 485 men worked in the heat, and the authors say so themselves: the small exposed group is why the range around 4.2 runs from 1.5 to 11.5, and why they ask for larger studies before anyone leans on the number [8]. In 5,114 men at one center in China, each 1.8 F rise in apparent temperature, a measure that combines temperature, humidity, and wind, over the 90 days before a semen sample was associated with about 0.12 percentage points lower progressive motility [25]. In 15,581 men in Denmark and Florida, the fastest sperm were collected in June and July and the slowest in December and January, in both countries, and the seasonal pattern held after accounting for outdoor temperature [26].

What sustained heat does to sperm

Sustained heat from sauna, hot tubs, and hot baths measurably lowers sperm health. This has been shown in multiple studies using sauna, a warming belt, and hot water baths [4, 5, 6, 7]. The exposures were repeated rather than one-off, most often two sessions a week typically for three months to cover a full sperm production cycle. What comes back is consistent across the heat sources: fewer sperm, less movement, fewer normally shaped sperm, more DNA damage, and more sperm dying off [4, 5, 6, 7].

Additionally, among eleven infertile men who used hot tubs, hot baths, or a whirlpool and then stopped, five saw their total motile sperm count rise [9]. Regardless of the heat source, heat is reliable enough at damaging sperm health that it has been tested as male contraception since the 1970s [1].

WHAT THE STUDIES SHOWmen heated on purposeA belt at 107 F, a bath at 109 F, a sauna at 185 F. All three lowered count and movement.7 studiesRead it

Warming belt. Fertile men wore a belt at about 107 F for 40 minutes a day, two days a week, for three months. Sperm concentration, movement, and normal shape all fell. Sperm DNA fragmentation (breaks in the genetic material inside the sperm) rose, along with three inflammation and cell-death markers in semen [4, 5].

Water bath. Twenty men with normal semen had their testicles warmed in a 109 F water bath for 30 minutes at a time, ten times, randomly assigned to ten days in a row or once every three days. Both schedules left more sperm with damaged DNA and more sperm dying off. Daily heating was worse [6].

Sauna. Ten men with normal sperm counts used a traditional sauna for 15 minutes twice a week for three months at about 185 F. Sperm count, movement, and DNA packaging all declined [7].

Hot tubs and baths. Among eleven infertile men who regularly used hot tubs, hot baths, or a whirlpool and then stopped, five improved. In those five, average sperm movement rose from 12 percent to 34 percent. The study had no comparison group, and the men who did not improve were more often smokers [9].

Taken together. A 2022 meta-analysis pooled nine heat studies. Sperm shape, movement, concentration, and total count were all worse in the heated men [16]. Six of the nine were deliberate heating experiments and four of those six are the studies above, so read it as a tally of this evidence rather than as separate confirmation of it.

Contraception. A review of French research since the 1970s reports that deliberately raising testicular temperature inhibited sperm production well enough to reach clinical trials as a contraceptive method. Side effects, chiefly loss of libido, and a high share of men who did not respond stopped it reaching use [1].

The recovery clock

Fortunately, heat-related sperm damage is reversible, it just takes time. Sperm shape returns to normal within about 73 days of stopping heat exposure, and the other sperm quality measures in the warming belt study returned to normal within three months [13, 4, 5]. Chromosome errors normalized within six months. Every sauna-related sperm health measure was also normal within six months [14, 7].

Figure 2What comes back, and when

Counting from the day heat exposure stops. One full cycle of sperm production runs about 64 days [12], which is why nothing moves much before then.

  1. Day 45Chromosome errors are still doubled [14]
  2. Day 73Sperm shape is back to normal [13]
  3. Day 90three monthsCount, movement, shape and DNA damage are back to normal after the warming belt [4, 5]
  4. Day 180six monthsChromosome errors are back to normal, and every sauna measure is normal too [14, 7]
Each row is what one study measured, and the studies used different heat sources, so read this as a sequence of findings rather than as one trial. The open marker is the one measure that was still abnormal at that point.
WHAT THE STUDIES SHOWhow long recovery takesSperm shape came back at 73 days. Chromosome errors took 180.5 studiesRead it

Five men wore underwear that held the testicles up against the body for about 15 hours a day for 120 days. Abnormally shaped sperm rose from day 34 of heating and returned to normal about 73 days after heating stopped [13]. In the same men, sperm with the wrong number of chromosomes (aneuploidy, which lowers the chance an embryo develops normally) had doubled 45 days after heating stopped and were back to normal at 180 days [14]. In the warming belt study, count, movement, shape, and DNA damage were back to normal three months after the belt came off [4, 5]. In the sauna study, every measure was normal again within six months of the last sauna [7].

Does cooling help?

Though studies are few, keeping the scrotum cool has real support. Five trials have tested it, and semen measures improved in most of them. For example, sperm concentration roughly doubled or more in two trials [27, 20]. In the most recent cooling device trial, cooling modestly raised sperm motility from 25.4 to 29.0 percent and sperm vitality from 64.8 to 71.7 percent. Notably, of the men who answered a questionnaire, 76.9 percent had worn the cooling device less than directed, citing discomfort [28]. This suggests that the observed improvement in sperm quality might have been greater with a more comfortable device that the men would have worn more consistently.

WHAT THE STUDIES SHOWcooling the scrotumIce packs doubled density in two thirds of 50 men. Most would not wear the newest device.5 studiesRead it

In one study, ice packs held in close-fitting underwear at night at least doubled sperm density in about two thirds of 50 men with low counts or low movement [27]. Nocturnal cooling with an air stream over 12 weeks lowered scrotal temperature by about 2 F and raised sperm concentration, total count, movement, and shape in men with low sperm quality [19]. The same cooling method in 20 infertile men with a history of undescended testicles lowered scrotal temperature by about 1.5 F and raised sperm concentration and total count by week 8, against 20 similar men followed without treatment [20]. Cooling underwear worn in cycles lowered median scrotal skin temperature by just over 1 F in three men monitored for 1,008 hours [21]. In the 40-man device trial, motility and vitality rose, and most men wore the device less than directed because it was uncomfortable [28].

The bottom line

Whether you are trying to conceive or simply want your testicles working under the conditions they were built for, think about your daily heat exposures and make the changes you can to lower your testicle temperature.

  • The easy and risk-free changes are breathable underwear, cooling breaks if your job is hot, and walking breaks if long stretches of sitting are part of your job [22, 8, 10].
  • Avoid habitual hot tubs and hot baths, and skip the sauna while you are trying to conceive [9, 7].
  • If you would rather not give up the sauna, wearable cooling is an inexpensive way to lower scrotal temperature [21].

References

Numbered by first appearance. Every study we could link is linked to its page in this library, where the full summary and appraisal sit alongside the original source.

  1. Soufir JC. Hormonal, chemical and thermal inhibition of spermatogenesis: contribution of French teams to international data with the aim of developing male contraception in France. Basic Clin Androl. 2017. doi:10.1186/s12610-016-0047-2.Read the study summary →
  2. Ivell R. Lifestyle impact and the biology of the human scrotum. Reproductive biology and endocrinology : RB&E. 2007. doi:10.1186/1477-7827-5-15.Read the study summary →
  3. Durairajanayagam D, et al. Causes, effects and molecular mechanisms of testicular heat stress. Reprod Biomed Online. 2015. doi:10.1016/j.rbmo.2014.09.018.Read the study summary →
  4. Zhang MH, et al. Changes in Levels of Seminal Nitric Oxide Synthase, Macrophage Migration Inhibitory Factor, Sperm DNA Integrity and Caspase-3 in Fertile Men after Scrotal Heat Stress. PLoS One. 2015. doi:10.1371/journal.pone.0141320.Read the study summary →
  5. Zhang MH, et al. Scrotal heat stress causes sperm chromatin damage and cysteinyl aspartate-specific proteinases 3 changes in fertile men. J Assist Reprod Genet. 2015. doi:10.1007/s10815-015-0451-0.Read the study summary →
  6. Rao M, et al. Transient scrotal hyperthermia affects human sperm DNA integrity, sperm apoptosis, and sperm protein expression. Andrology. 2016. doi:10.1111/andr.12228.Read the study summary →
  7. Garolla A, et al. Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Hum Reprod. 2013. doi:10.1093/humrep/det020.Read the study summary →
  8. Han N, et al. Occupational Heat Exposure and Fertility Stress as Independent Factors of Low Semen Quality: A Multidimensional Analysis. Am J Mens Health. 2026. doi:10.1177/15579883261454721.Read the study summary →
  9. Shefi S, et al. Wet heat exposure: a potentially reversible cause of low semen quality in infertile men. Int Braz J Urol. 2007. doi:10.1590/s1677-55382007000100008.Read the study summary →
  10. Hjollund NH, et al. The relation between daily activities and scrotal temperature. Reprod Toxicol. 2002. doi:10.1016/s0890-6238(02)00026-6.Read the study summary →
  11. Hjollund NH, et al. Impact of diurnal scrotal temperature on semen quality. Reprod Toxicol. 2002. doi:10.1016/s0890-6238(02)00025-4.Read the study summary →
  12. Misell LM, et al. A stable isotope-mass spectrometric method for measuring human spermatogenesis kinetics in vivo. J Urol. 2006. doi:10.1016/s0022-5347(05)00053-4.Read the study summary →
  13. Abdelhamid MHM, et al. Mild experimental increase in testis and epididymis temperature in men: effects on sperm morphology according to spermatogenesis stages. Transl Androl Urol. 2019. doi:10.21037/tau.2019.11.18.Read the study summary →
  14. Abdelhamid MHM, et al. Experimental mild increase in testicular temperature has drastic, but reversible, effect on sperm aneuploidy in men: A pilot study. Reprod Biol. 2019. doi:10.1016/j.repbio.2019.06.001.Read the study summary →
  15. Setchell BP. The Parkes Lecture. Heat and the testis. J Reprod Fertil. 1998. doi:10.1530/jrf.0.1140179.Read the study summary →
  16. Hoang-Thi AP, et al. The Impact of High Ambient Temperature on Human Sperm Parameters: A Meta-Analysis. Iran J Public Health. 2022. doi:10.18502/ijph.v51i4.9232.Read the study summary →
  17. Sheynkin Y, et al. Increase in scrotal temperature in laptop computer users. Hum Reprod. 2005. doi:10.1093/humrep/deh616.Read the study summary →
  18. Sheynkin Y, et al. Protection from scrotal hyperthermia in laptop computer users. Fertil Steril. 2011. doi:10.1016/j.fertnstert.2010.10.013.Read the study summary →
  19. Jung A, et al. Improvement of semen quality by nocturnal scrotal cooling and moderate behavioural change to reduce genital heat stress in men with oligoasthenoteratozoospermia. Reproduction. 2001. doi:10.1530/rep.0.1210595.Read the study summary →
  20. Jung A, et al. Improvement of semen quality by nocturnal scrotal cooling in oligozoospermic men with a history of testicular maldescent. Int J Androl. 2005. doi:10.1111/j.1365-2605.2004.00517.x.Read the study summary →
  21. Zumstein V, et al. Stay cool! Special underwear for cyclic cooling significantly decreases scrotal skin temperature. Cent European J Urol. 2021. doi:10.5173/ceju.2021.r1.0019.3.Read the study summary →
  22. Jung A, et al. Influence of the type of undertrousers and physical activity on scrotal temperature. Hum Reprod. 2005. doi:10.1093/humrep/deh697.Read the study summary →
  23. Zleczewski M, et al. Garment fit, scrotal thermoregulation, and male fertility outcomes: a narrative review. Transl Androl Urol. 2026. doi:10.21037/tau-2026-1-0139.Read the study summary →
  24. Bujan L, et al. Increase in scrotal temperature in car drivers. Hum Reprod. 2000. doi:10.1093/humrep/15.6.1355.Read the study summary →
  25. Liu G, et al. Quantifying the exposure-response relationship between temperature exposure and semen quality. Front Public Health. 2026. doi:10.3389/fpubh.2026.1813888.Read the study summary →
  26. Lassen E, et al. Seasonal trends in sperm quality in Denmark and Florida. Reprod Biol Endocrinol. 2026. doi:10.1186/s12958-026-01537-w.Read the study summary →
  27. Mulcahy JJ. Scrotal hypothermia and the infertile man. J Urol. 1984. doi:10.1016/s0022-5347(17)49694-7.Read the study summary →
  28. Benidir T, et al. Evaluation of patient compliance with the use of scrotal cooling devices. F&S Rep. 2021. doi:10.1016/j.xfre.2021.06.007.Read the study summary →