Short answer: yes. Regular sauna use raises the temperature of your testicles, and a body of research links that heat to a temporary drop in sperm count and motility. The good news: it is usually reversible, and you do not have to give up the sauna to manage it.
Here is what the evidence actually says, what it means if you are trying for a baby, and what you can realistically do about it.
Why heat matters down there
Your testicles sit outside the body for a reason. Sperm are made best at around 2 to 3°C below core body temperature, which is why the scrotum hangs away from the warmth of the torso and constantly adjusts to regulate its own temperature. Anything that overrides that system and holds the testicles hot for a while can interfere with sperm production. A sauna does exactly that.
What the research shows
Studies that put healthy men through repeated sauna sessions have measured real, measurable dips in sperm output while the heat exposure continued. It is the same reason fertility specialists routinely tell men who are trying to conceive to ease off hot tubs, saunas, and long hot baths.
The pattern across the literature is consistent: sustained scrotal heat is associated with lower sperm count and motility, and the effect tends to reverse once the heat stops.
Cooling has been studied from the other direction too. Trials on scrotal cooling have reported improvements in sperm concentration, motility, and shape over several weeks. You can read more about the published research we lean on here.
How long does it take to recover?
Sperm take roughly two to three months to mature, so the effect of a hot phase is not instant, and neither is the recovery. If you cut the heat, measures generally rebound over about one full sperm cycle. That lag is also why timing matters when you are trying to conceive: what you do this month shows up in a sample a couple of months later.
Who should care most
If you are trying for a baby, this is worth taking seriously, because heat is one of the few fertility factors you can actually control. And it is not only saunas. Hot tubs, long hot baths, a laptop run hot on your lap, tight insulating underwear, and even long hot commutes all push in the same direction. Sauna is simply the clearest example.
Do you have to quit the sauna?
No, and this is the part most articles get wrong. The honest options are simple: use heat less often, keep sessions shorter, or keep the testicles cool while you enjoy the heat. Plenty of men do not want to give up something they find genuinely good for stress and recovery, and they should not have to.
That is the whole reason cooling exists as a category. The biohacker crowd has been doing a rough version for a while: pressing a bag of ice against the groin during a session. It works in principle, but loose ice is awkward, it slides around, and pressed straight on skin it can cause an ice burn.
Frozen peas, or something built for the job
A bag of frozen peas in a tea towel is the classic free option, and a urologist will happily suggest it. The catch is that almost nobody keeps it up, because it is fiddly and unpleasant. The point of an engineered solution is not that it cools better than ice. It is that you will actually use it: a wearable liner with a phase-change insert that sits where it needs to, stays at a comfortable cool rather than freezing solid, and travels in an insulated case. That is what we built NUMBNUTS to do.
Quick answers
How often is too often?
There is no single threshold. Frequent, long, hot sessions during a conception window are the thing to watch; the occasional sauna is unlikely to matter much. If you are trying to conceive, treat the months that count differently from the rest of the year.
Does a sauna affect testosterone?
Heat mainly affects sperm production. Do not use cooling expecting a testosterone change, because that is not what the evidence shows, and we make no such claim.
What about hot tubs and hot baths?
Same mechanism. Anything that holds the scrotum hot for a sustained period can have the same effect, which is why the advice extends well beyond saunas.
The honest caveats
A few things worth being straight about. Experts do not all agree on how much cooling helps, and cooling is not a treatment for infertility. If you have a real fertility concern, see a doctor and get a proper semen analysis rather than guessing. What the research does support is narrower and more useful: heat is linked to lower sperm measures, and keeping cool can help protect them.
If you love the heat and want the simple way to look after the basics, that is exactly what we made.