Does sauna lower testosterone? What the research actually says

Short answer: no, the research does not show that sauna use lowers testosterone. It shows something different and more specific, which is that heat affects sperm production. Those are two separate jobs performed by two separate cell populations, and the internet routinely collapses them into one claim.

The testis does two unrelated jobs

Inside the testis, sperm are made in the seminiferous tubules by the germinal epithelium. Testosterone is made outside those tubules, by Leydig cells sitting in the tissue between them. Same organ, different machinery, different sensitivities.

This is why "sauna hurts sperm count" and "sauna lowers testosterone" are not the same statement and do not stand or fall together. The germinal epithelium is famously temperature sensitive. That is the reason the testes sit outside the body cavity in the first place, running a few degrees below the 37 degrees Celsius maintained everywhere else. Leydig cells do not carry the same requirement, and the evidence reflects that.

What was actually measured

The cleanest hormone data on sauna comes from Kukkonen-Harjula and colleagues, published in the European Journal of Applied Physiology and Occupational Physiology in 1989. Eight healthy young men went through three different sauna exposures: 80 degrees Celsius dry, 100 degrees Celsius dry, and 80 degrees Celsius moving into humid conditions. Oral temperature rose by 1.1, 1.9 and 3.2 degrees Celsius respectively, so these were real physiological loads and not token sessions.

Prolactin responded dramatically, rising two to ten fold. Beta endorphin, ACTH and growth hormone all rose at the higher temperatures. Cortisol went down at 80 and at 100 degrees dry, which surprises people who assume heat is a straightforward stressor.

Testosterone increased in the most demanding condition, the humid one that pushed core temperature up by more than three degrees. It was not reported to fall in any of the three.

Eight men, acute exposures, hormones measured around the sessions. That is the size and shape of the evidence, and it should be read as a signal about the direction of the acute response rather than as a precise number.

So where did the "sauna kills testosterone" idea come from

Mostly from a game of telephone with the sperm research. The finding that travels well is that regular sauna use measurably reduces sperm count and motility. That is real and it is well documented. Garolla and colleagues showed it in Human Reproduction in 2013: ten men, two sessions per week for three months at 80 to 90 degrees Celsius, with strongly impaired sperm count and motility at the end of the exposure period and full return to baseline six months after stopping.

Somewhere between that paper and a forum post, "sperm production" became "male hormones" became "testosterone". It is an understandable slip and it is still wrong. Garolla measured semen parameters and molecular markers of spermatogenesis. That study is not a testosterone study.

There is a second reason the confusion sticks, which is that a claim about testosterone is more marketable than a claim about chromatin condensation. Be suspicious of anyone whose product story requires the testosterone version to be true.

What this does and does not license you to conclude

It does not license the conclusion that sauna is endocrinologically inert. The 1989 data shows sauna moving several hormones around substantially, and acute responses in eight men are not the same thing as long term effects in a population.

It does license dropping one specific worry. If your concern about the sauna was that it is quietly suppressing your testosterone, the available evidence does not support that concern, and the loudest version of it on the internet is a misreading of a sperm study.

The concern that survives is the narrow one. Heat affects sperm production, the effect tracks with cumulative exposure, and it reverses on a timescale of months rather than weeks. If that is relevant to your situation, it is worth a conversation with a doctor rather than a conversation with a search engine.

Where KOLDWR sits in this

Squarely out of it. KOLDWR is a boxer brief with a sewn in front pocket that holds a frozen gel pack, and two packs are included, so cooling stays in place through a full sauna session. Its entire function is to keep the temperature down in the one region that is supposed to be cooler than the rest of you.

We make no claim that it raises testosterone. We make no claim that it improves fertility or sperm count either. Nobody has run the trial that would let anyone make those claims honestly, and we would rather say so than sell you a hormone story. What is established is that heat exposure is the variable in the research, and reducing local heat exposure is the mechanically obvious lever. More on how we draw that line is on the science page.

Common questions

Does cold exposure raise testosterone?
Not in any way that the evidence supports as a reliable, lasting effect, and we are not going to pretend otherwise in order to sell cooling underwear.

Should men trying to conceive avoid the sauna?
That is a question for a doctor. The relevant evidence is about sperm parameters, not hormones, and it is summarized in our article on whether sauna lowers sperm count.

What about the prolactin spike?
It is large and it is real, and it is also an acute response to heat that has been observed for decades. It is not evidence of a problem on its own.

Does the temperature of the room change the hormone response?
Yes. In the 1989 study the hormonal responses scaled with how much core temperature actually rose, which depended on both heat and humidity. A humid 80 degree room was more demanding than a dry 100 degree one.

Related reading

Does sauna use lower sperm count? What the research actually says
How long does sperm count take to recover after sauna heat?
Does scrotal cooling actually work? What the research shows, and what we do not claim
How to protect your testicles in a sauna
Cooling underwear for the sauna: how the options actually differ
Sauna temperature and scrotal temperature: the numbers that matter

Sources

Kukkonen-Harjula K, Oja P, Laustiola K, Vuori I, Jolkkonen J, Siitonen S, Vapaatalo H. Haemodynamic and hormonal responses to heat exposure in a Finnish sauna bath. European Journal of Applied Physiology and Occupational Physiology, 1989, volume 58, pages 543 to 550.

Garolla A, Torino M, Sartini B, Cosci I, Patassini C, Carraro U, Foresta C. Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Human Reproduction, 2013, volume 28, issue 4, pages 877 to 885.