Regular exposure to heat temporarily lowers sperm count. That single finding answers most of the question about heat and male fertility, and it is one of the most consistent results in reproductive research. Testicles hang outside the body because sperm production requires a temperature a few degrees below core body temperature. Heat exposure closes that gap. The effects on sperm are real, and they are reversible.
Why the testicles need cooler temperatures
The scrotum is a temperature regulation system. The cremaster muscle raises and lowers the testicles in response to cold and heat. Sweat glands cool the surface. A network of veins called the pampiniform plexus acts as a countercurrent heat exchanger, cooling incoming arterial blood before it reaches the testicular tissue, and this mechanism is one of the reasons the testicles can stay cooler than the rest of the body. All of this exists because the cells that produce sperm, germ cells and Sertoli cells, work best below core temperature. A review by Durairajanayagam and colleagues in Reproductive BioMedicine Online (2015) describes this mechanism in detail.
When external heat raises scrotal temperature, sperm production slows. This is not a controversial finding. The question for most men is practical: how much heat, how often, and for how long before the effect shows up in a semen analysis.
What the research shows about regular heat exposure
Sauna-level heat temporarily lowers sperm count and can worsen morphology, meaning the shape of individual sperm (Garolla et al., Human Reproduction, 2013). The study compared men with regular sauna exposure to men without it. Sperm counts and morphology were lower in the sauna group. When the men with regular sauna exposure stopped using the sauna, their sperm parameters improved.
Wet heat from hot tubs matters too. Shefi and colleagues published a study in Fertility and Sterility (2007) following men who stopped regular hot tub and sauna use. Semen parameters recovered after the heat exposure stopped, following the roughly three-month cycle of sperm production.
Laptops belong on a desk. Sheynkin and colleagues studied scrotal temperature in men sitting with a laptop on the lap and found that scrotal temperature rose even when using a lap pad, because the closed-thigh sitting posture traps heat against the body and the laptop's exhaust adds more (Human Reproduction, 2005).
Everyday clothing choices also shape scrotal temperature. Jung and colleagues (Human Reproduction, 2005) and Mieusset and colleagues (Journal of Andrology, 2007) found that tighter underwear and prolonged sitting raise scrotal temperature relative to looser underwear and movement. Minguez-Alarcon and colleagues (Human Reproduction, 2018) found that men who reported wearing looser, boxer-style underwear had higher sperm concentration and total count in a fertility-center cohort.
The recovery timeline
Heat-related sperm changes reverse once heat exposure stops. Sperm production takes about 74 days from start to finish. A man's ejaculate today reflects conditions from roughly two and a half months ago. When heat exposure stops, sperm parameters can recover within one to two sperm production cycles in most men. The Shefi et al. (2007) study documented this recovery pattern directly. Men who stopped wet heat exposure showed improvements in sperm parameters over several months.
The practical implication: if a semen analysis comes back low while you're using a sauna or hot tub several times a week, heat exposure might be a factor, and research shows that reducing or pausing heat exposure for a few months allows sperm parameters to recover in many men. Whether this is the right move for you personally is a conversation for a doctor, not a blog post.
Heat and testosterone: less settled territory
The relationship between heat and testosterone is less settled than the relationship between heat and sperm production. Heat stresses the temperature-sensitive cells in the testicles. A single sauna session does not crash testosterone. Some online sources claim that sauna use boosts testosterone. The weight of research does not support that claim. The long-term effect of regular heat exposure on circulating testosterone has not been settled by large trials.
Practical adjustments if fertility is a concern
If you're thinking about fertility, several physical adjustments are worth considering. None of these are prescriptions. They are options rooted in the temperature mechanism described above.
One option is to look at your heat exposure pattern directly. A man who sits in a sauna four times a week and is trying to conceive might temporarily cut back or pause sauna use. A man who uses a hot tub daily might do the same. The research on reversibility indicates that a pause of two to three months aligns with the sperm production cycle. For some men, a cold pack over the groin during a sauna session keeps the testicles cooler in the moment. That is a physical cooling measure, not a fertility guarantee.
Another angle is all-day heat. Tight polyester underwear holds heat against the body, while a laptop on the lap for hours at a time adds direct heat. Long stretches of sitting without standing compound the problem. Loose-fitting, breathable underwear lets air move and keeps the testicles closer to the temperature they prefer. This physical effect is measurable. It is the reasoning behind designs like Oakman's boxer briefs, which use breathable fabric and a non-constrictive fit to reduce trapped heat during the day.
Occupational heat is worth a look too. Welders, bakers, foundry workers, and men in similar roles face regular heat exposure as part of the job. If you work in a hot environment and fertility is a concern, a conversation with an occupational health provider or a urologist is worth having.
A semen analysis is the only way to know your baseline. Sperm parameters vary between men and even within the same man across time. Research describes patterns across populations. It cannot tell you what is happening in your body specifically. Tracking whether heat avoidance makes a measurable difference for you requires a before and after comparison.
Where heat fits among other fertility factors
Heat exposure is one modifiable factor among many. Population-level sperm counts have declined over the past several decades (Levine et al., Human Reproduction Update, 2023), which means the backdrop for individual fertility concerns is a broader trend that researchers attribute to a range of environmental and lifestyle factors. Environmental exposures, diet, sleep, and stress all influence male reproductive health. Heat is worth understanding because it is specific, measurable, and within a man's direct control. Not everything in modern life meets that description.
Individual responses vary. Some men use saunas regularly and have no measurable fertility issues. The studies describe population-level patterns, not individual predictions. If you're concerned about fertility, consult a healthcare professional. The information here is educational, not a substitute for medical evaluation.
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.