Does scrotal cooling actually work? What the research shows, and what we do not claim

There are two questions hiding inside this one, and separating them is the whole answer. Does scrotal cooling lower scrotal temperature? Yes, and that part is not really in dispute. Does lowering scrotal temperature improve fertility outcomes? That has been studied, the trend is positive, and the evidence is not strong enough for anyone to promise you an outcome.

We sell cooling underwear, so you should read the rest of this with that in mind. We have tried to write the version we would want to read if someone else were selling it.

Question one: is the tissue actually that temperature sensitive

Yes, and by a smaller margin than most people expect. The testes sit outside the body cavity because sperm production requires a temperature below core, and the gap involved is a few degrees, not tens of degrees.

Michael Bedford laid this out in Biology of Reproduction in 2015 in a review titled Human Spermatozoa and Temperature: The Elephant in the Room. Two figures from it are worth carrying around. In animal work, raising testis temperature by roughly 1.5 degrees Celsius was enough to reduce sperm production and produce abnormalities in sperm formation. In humans, an increase in scrotal temperature of approximately 4 degrees Celsius caused by close fitting clothing has a negative impact on the germinal epithelium and on the epididymis.

Four degrees from trousers. That is the scale we are operating at. It tells you why a sauna at 80 to 100 degrees Celsius is a serious thermal input to this tissue, and it also tells you that an intervention does not need to be dramatic to be meaningful, because the system does not have much headroom in the first place.

Question two: does cooling improve fertility outcomes

Here the honest answer is that nobody knows well enough to promise you anything.

The best summary is a systematic review by Nikolopoulos and colleagues, published in the Journal of Obstetrics and Gynaecology in 2013. The authors searched EMBASE from 1980 to 2010 and MEDLINE from 1950 to September 2010 for studies on scrotal cooling and male fertility. Eight articles met the inclusion criteria.

Their conclusion has two halves and both matter. The evidence was insufficient to draw definitive conclusions. A positive trend of improved male fertility was, however, observed. They ended by calling for well designed randomised controlled trials, which is what researchers say when the existing literature is suggestive and structurally weak.

Eight studies, heterogeneous in design, mostly small, spanning three decades of methods. That is not a body of evidence you build a health claim on. It is a body of evidence that says the idea is worth testing properly and has not been.

What the sauna research adds

The strongest single result in this whole area is not a cooling study at all. It is a heating study.

Garolla and colleagues, writing in Human Reproduction in 2013, put ten men with normal semen parameters through two sauna sessions a week for three months, fifteen minutes each at 80 to 90 degrees Celsius. Sperm count and motility were both strongly impaired at the end of that period, at P less than 0.001, and molecular markers of sperm production moved with them. Six months after stopping, everything was back to baseline.

That study establishes the direction of the relationship cleanly. Add heat to this tissue on a repeated schedule and measurable things get worse. Remove the heat and they recover.

What it does not establish, and what no published trial establishes, is that intervening to reduce heat during the session produces the same benefit as skipping the session. That is a reasonable inference. It is not a demonstrated result, and we are not going to present it as one.

What we claim, and what we refuse to claim

Our claim is thermal and nothing more. KOLDWR is a boxer brief with a sewn in front pocket holding a frozen gel pack, and two packs are included. It keeps cooling in contact and in position for a full sauna session instead of a bag of ice sliding off your lap. It reduces heat exposure at the place where the research says heat exposure matters.

We do not claim it improves fertility. We do not claim it improves sperm count, motility or morphology. We do not claim it affects testosterone. We do not claim it helps anyone conceive. Those claims would require trials that have not been run, and a company that makes them is either not reading the literature or is counting on you not to.

If you want the fuller version of how we draw that line, it is on the science page.

How to think about it if you are deciding

The framing that seems most honest is this. There is a well documented effect of heat on sperm production, the tissue involved is sensitive to changes of a couple of degrees, and the options for reducing that exposure are: use the sauna less, use it for less time, sit lower on the bench, or cool the area directly and keep the session unchanged.

The first three all cost you something you presumably want, which is the sauna. The fourth costs 49 dollars once. Whether the fourth delivers a fertility benefit is unproven and we have said so three times now. Whether it reduces heat exposure is a question about thermodynamics rather than about biology, and the answer there is straightforward.

If your situation is medical, meaning you are being evaluated for fertility or are actively trying to conceive, this article is not the input you need. Bring the Garolla paper and the Nikolopoulos review to a doctor and let someone qualified read them with your history in front of them.

Common questions

Is there a randomised controlled trial of scrotal cooling?
Not one that settles the question. The 2013 systematic review found eight studies in total and explicitly called for well designed randomised controlled trials, which is the standard way of saying the ones that exist are not sufficient.

How much cooling is enough?
Nobody has established a threshold in humans that maps to an outcome. The Bedford review gives a sense of the scale the tissue responds at, which is degrees rather than tens of degrees, but a target number would be an invention.

Is a bag of frozen peas equivalent?
Thermally it is in the same category. Practically it slides, it leaks and it does not survive a sauna bench. That is a product argument, not a scientific one, and we will not dress it up as a scientific one.

Can cooling be overdone?
Direct contact between frozen material and skin can cause a cold burn, which is why the gel pack sits in a fabric pocket rather than against skin. If something hurts, take it out.

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 sauna lower testosterone? What the research actually says
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

Nikolopoulos I, Osman W, Haoula Z, Jayaprakasan K, Atiomo W. Scrotal cooling and its benefits to male fertility: a systematic review. Journal of Obstetrics and Gynaecology, 2013, volume 33, issue 4, pages 338 to 342.

Bedford JM. Human Spermatozoa and Temperature: The Elephant in the Room. Biology of Reproduction, 2015, volume 93, issue 4, article 97.

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.