Sperm counts have fallen sharply over the past few decades, and the largest drivers appear to be environmental and lifestyle exposures, not the occasional sauna. Sauna-level heat does lower sperm production for a while, but that effect reverses once the heat stops. The exposures that seem to matter most are the everyday ones: microplastics, plastic-derived chemicals, and long stretches of heat held against the body.
A number worth sitting with: a 2017 meta-analysis by Levine and colleagues pooled 185 studies and nearly 43,000 men and found that sperm concentration among men in North America, Europe, and Australia fell by more than 50 percent between 1973 and 2011. [1] A 2022 update from the same group extended the picture globally and reported that the decline has, if anything, sped up since 2000. [2] That is a change measured in a single generation, which points at environment rather than genetics.
Most fertility advice online hammers the same short list: wear boxers, keep the laptop off your lap, skip the sauna. The message men absorb is that heat is the whole story. Heat matters, and the everyday kind matters most, but it is not what best explains a fifty percent drop in a single generation.
Yes, heat lowers sperm, and here is what that actually means
The testicles sit outside the body for a reason. Sperm production works best a few degrees below core body temperature, which is why the scrotum tightens and relaxes to hold that gradient. When the testicles get too warm, sperm production slows.
Sauna-level heat is a clear example. In a 2013 study, Garolla and colleagues exposed men to repeated Finnish sauna sessions and measured a real drop in sperm count and motility. [3] The important half of that study is the recovery: the changes reversed once the men stopped the heat exposure, because sperm production needs the testicles cooler than core temperature and resumes when that cooling returns. A 2007 study by Shefi and colleagues showed the same pattern with wet heat: men who stopped regular hot-tub and bath exposure saw their semen quality recover in the months afterward. [4]
So the honest version is not that heat is harmless, and not that a sauna somehow helps. Sauna-level heat produces a temporary, reversible slowdown in sperm production. It is a production dip that recovers, not lasting damage. That is very different from the second category below, which does not simply wash out.
And it is not only sperm. The same heat slows testosterone production at the cellular level: warm the Leydig cells that make most of a man's testosterone and the enzymes they use to build it slow down, which is measured in animal and cell studies. [5][6] Whether that daily heat moves a healthy man's circulating testosterone over a lifetime has not been tested in a long trial, but the mechanism is real and that study should be done. The point is that warming the testicles disrupts the whole environment they are built to run, sperm and testosterone alike, whether or not you are trying to conceive.
What is actually driving the decline
The usual fertility levers, diet and sleep and stress, are real, but they cannot explain a 50 percent drop in one generation. The exposures that track the timeline are the synthetic chemicals that surround daily life, especially the endocrine disruptors: compounds like phthalates, BPA, and PFAS that interfere with hormone signaling.
Then there is the plastic itself. In 2024, researchers at the University of New Mexico reported finding microplastics in every human testicle sample they examined, with polyethylene, the plastic in grocery bags, the most common type. [7] The concentration in human testes ran higher than in the animal samples they compared against. These particles are not something you can sweat out or offset with a colder shower.
This is why the heat-versus-chemicals framing matters. You can skip the sauna all year and it will not stop phthalates leaching from a warm plastic takeout container, or clear the microplastics already lodged in tissue. The reversible thing gets almost all the attention. The harder-to-reverse thing gets almost none.
Two kinds of heat worth managing
If heat disrupts that environment, there are two exposures worth handling. The first is the constant, low-grade heat that sits against the testicles all day: a laptop on the lap for hours, tight synthetic underwear that traps warmth, and long uninterrupted stretches of sitting. That heat never gets a chance to cool off, so it keeps the testicles warm far longer than a short sauna does, and it is the one most men never think about.
The second is the sauna. A whole-body sauna is one of the best things a man can do for his health, and there is no reason to give it up. But it heats the testicles along with everything else, and the fix is not to skip it, it is to keep the testicles cool while you sit in the heat. Active cooling belongs during the session, since the disruption happens while the testicles are warm and a cold shower afterward does not undo it. That is why many men who sauna use a cold pack held against the testicles during the session: it keeps them at the cooler temperature the body is built to make sperm and testosterone at, rather than letting the heat disrupt it. This holds even if you are not trying to conceive, because the temperature-sensitive machinery is the same either way.
That is the whole idea behind Oakman: breathable, airflow-first boxer briefs for the everyday heat, and a slim removable cold pack for the sauna. The products make no claim on your hormones or your sperm. They keep the testicles cooler, which is simply the temperature the body is built to run them at. Pair that with getting the laptop onto a desk and breaking up long sitting, and you have handled both kinds of heat.
Practical steps, highest leverage first
1. Cut your exposure to endocrine disruptors
This is the change most advice skips, and the one the timeline points at. A few concrete moves:
- Stop microwaving food in plastic; heat accelerates chemical leaching.
- Switch to stainless steel or glass for water and leftovers.
- Choose fresh or frozen vegetables over canned where you can, since can linings can contain BPA.
- Favor cast iron or ceramic over older nonstick cookware.
- Check personal care products for phthalates and parabens.
2. Eat for antioxidant defense
Sperm cells are vulnerable to oxidative damage, and dietary patterns rich in vegetables, fruit, nuts, fish, and olive oil are associated with better semen quality in the research. Whole foods carry the strongest signal here, not megadose supplements. Zinc, selenium, and folate show up repeatedly, which points at oysters, pumpkin seeds, Brazil nuts, eggs, and leafy greens rather than a pill.
3. Protect your sleep
Much of a man's testosterone is produced during sleep, and short sleep is associated with lower testosterone and weaker sperm parameters. Seven to eight hours is doing real work.
4. Move, without cooking your groin
Moderate activity helps hormone profiles and lowers oxidative stress. The caveat is heat and compression: hours on a bike saddle adds both. Mix in resistance work and get off the saddle now and then.
5. Handle both kinds of heat
Keep the everyday heat down: laptop off the lap, break up long sitting, and pick breathable underwear over a tight synthetic fit. And if you use the sauna, keep the testicles cool during the session with a cold pack, so you get the sauna's health benefits without warming the one place built to stay cool. If you are actively trying to conceive or already have a low count, get a semen analysis so you are working from data, and talk to a doctor before big changes.
The bottom line
The standard fertility conversation treats men as fragile and treats heat as the villain. The evidence tells a calmer, more useful story. Sauna-level heat causes a real but temporary and reversible dip in sperm production. The harder problem is the chemical load that earlier generations never carried, the phthalates and PFAS and the microplastics now turning up in testicular tissue. If you are going to spend effort somewhere, spend it on the chemical load and on keeping the testicles cool, breathable underwear for the everyday heat and a cold pack for the sauna, rather than on giving up the sauna's real health benefits.
Frequently asked questions
does using a sauna permanently hurt your sperm count
No. Sauna-level heat causes a temporary, reversible slowdown in sperm production rather than lasting damage. Garolla and colleagues (2013) measured a real drop in sperm count and motility from repeated sauna sessions, and the changes reversed once the heat exposure stopped, because sperm production needs the testicles a few degrees cooler than core body temperature and resumes when that cooling returns.
what is actually driving the long-term decline in sperm counts
The largest drivers appear to be environmental and lifestyle exposures rather than the occasional sauna. A 2017 meta-analysis by Levine and colleagues found sperm concentration in Western men fell by more than 50 percent between 1973 and 2011, and a 2022 update reported the decline has accelerated since 2000. That timeline points at endocrine-disrupting chemicals such as phthalates, BPA, and PFAS, which interfere with hormone signaling, rather than at heat, which is reversible.
have microplastics really been found in human testicles
Yes. In 2024, researchers at the University of New Mexico reported finding microplastics in every human testicle sample they examined, with polyethylene, the plastic used in grocery bags, the most common type. Unlike the reversible dip from heat, these particles are not something the body simply clears with cooling.
does everyday heat matter more than an occasional sauna
Everyday heat never gets a chance to cool off, so a laptop on the lap for hours, tight synthetic underwear, and long uninterrupted sitting keep the testicles warm far longer than a short sauna session does. That constant low-grade heat is worth handling with breathable underwear, a laptop on a desk, and breaks from sitting. The sauna is a shorter, reversible exposure and worth keeping for its health benefits, so the move there is to keep the testicles cool during the session with a cold pack rather than to skip it. Both kinds of heat disrupt the same temperature-sensitive machinery the testicles use to make sperm and testosterone.
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.
References
- Levine H, et al. (2017). Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update. [Link]
- Levine H, et al. (2022). Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries. Human Reproduction Update. [Link]
- Garolla A, et al. (2013). Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Human Reproduction. [Link]
- Shefi S, et al. (2007). Wet heat exposure: a potentially reversible cause of low semen quality in infertile men. International Brazilian Journal of Urology. [Link]
- Durairajanayagam D, Agarwal A, Ong C. (2015). Causes, effects and molecular mechanisms of testicular heat stress. Reproductive BioMedicine Online. [Link]
- Cai H, Qin D, Peng S. (2021). Responses and coping methods of different testicular cell types to heat stress: overview and perspectives. Bioscience Reports. [Link]
- Hu CJ, et al. (2024). Microplastic presence in dog and human testis and its potential association with sperm count and weights of testis and epididymis. Toxicological Sciences. [Link]