Scrotal cooling: mechanisms, evidence grades and open questions

The term covers several different things. In research it usually means avoiding heat: loose clothing, less sitting, no hot baths. On social media it more often means active cooling with cold objects, cold water or special garments.

The difference matters. Avoiding overheating has some support in observational studies. Actively cooling below normal temperature has almost no support at all, because it has barely been studied.

1. Position. The testes sit outside the abdomen and normally stay a few degrees below core temperature.
2. Skin. Scrotal skin is thin, lacks subcutaneous fat and has many sweat glands. Evaporating sweat cools.
3. Muscles. The cremaster muscle and a muscle in the skin draw the testes closer to the body in cold and relax them in heat.
4. Blood vessels. A network of veins around the artery, the pampiniform plexus, works as a heat exchanger: warm incoming blood is cooled by cooler outgoing blood.
5. Behaviour. We sit with legs apart, move away from heat or change clothes. That is part of regulation too.

Anything that traps heat around the scrotum or holds it closer to the body can raise temperature slightly: tight underwear and trousers, long sitting, a laptop on the lap, hot baths and saunas, fever and hot workplaces.

The effect of each factor is small and hard to measure. Studies often use skin temperature sensors, which can themselves affect the result. That makes the field difficult to research.

We use the same scale as on our Science page: A for strong evidence, B for moderate, C for weak and D for anecdote.

• A: Sperm production works best below core temperature, and substantial heating affects it. This is basic physiology.
• B: Regular sauna use temporarily lowered lab values in healthy men in one small study (Garolla et al., 2013). Loose underwear was associated with higher sperm concentration in a large observational study (Mínguez-Alarcón et al., 2018).
• C: That local cooling after heat counteracts the effect of the heat. Plausible in theory, but not tested in controlled studies.
• D: That active cooling raises testosterone, boosts energy or improves performance. Common on social media, without scientific support.

A 2026 narrative review in Translational Andrology and Urology examined research on garment fit and temperature regulation. Its conclusion was cautious: fit and local temperature are reasonable factors to consider, but intervention studies showing effects on real outcomes such as pregnancy are missing.

The review also notes that many studies are small, measurement methods vary and lifestyle factors such as weight, smoking and sleep are often not properly controlled.

There is a clinical context where temperature is discussed: varicocele, enlarged veins in the scrotum, which can raise local temperature. It is assessed and treated by doctors.

There have also been small studies in which men with reduced values used cooling devices under medical supervision. Results are mixed and samples small. That is not the same as healthy men cooling themselves day to day.

• Cold should never be directly against the skin. Always keep fabric in between.
• Keep it short: 15–20 minutes is enough, then take a break.
• Stop if it hurts, goes numb or the skin turns white or red.
• Never use ice straight from the freezer unprotected, and do not fall asleep with something cold against your body.
• If you have reduced sensation, diabetes or circulation problems, ask a healthcare professional first.

• How much does temperature actually drop with different methods, and for how long?
• Does cooling after heat matter, or is it only avoiding heat that counts?
• Is there a lower limit below which cooling becomes pointless or harmful?
• How large is the effect compared with weight, smoking, alcohol and sleep?

One thing that is easy to miss in this debate is how large the differences between men are to begin with. Two healthy men of the same age can have completely different sperm concentrations, and the same man also varies over time. Sleep, infections, alcohol, exercise, stress and time since last ejaculation affect the values more than most single lifestyle factors.

That makes it hard to interpret a single study where men were exposed to heat and then measured. A small drop in the average may come from the heat, but it may also sit within normal variation. That is why researchers prefer to look at groups over time, and at several measures at once: concentration, motility, shape and DNA damage.

When we say that the effect of changing a single habit is small, we mean it is almost always smaller than everyday variation. That is not an argument for ignoring heat, but it explains why a change rarely shows up straight away.

• Move more often during the working day. Long periods of sitting raise scrotal temperature more than a sauna round.
• Wear loose-fitting underwear and trousers when you can. The effect is small but free.
• Avoid hot baths every evening if you are planning children within a few months. Once or twice a week is probably irrelevant.
• Get enough sleep. Sleep is the single biggest factor you control that interacts with hormones and recovery.
• If you use the sauna daily: sit a few minutes shorter now and then, drink before the session and let your body cool afterwards.

If you are trying for a baby and want to cut back on heat, it is reasonable to do so for three months, since it takes roughly that long to form new sperm. Shorter breaks rarely show up in measurements.

There is no reason to stop using the sauna altogether. It is easier to lower the temperature or shorten the rounds, and to move the last session earlier in the evening. If you are being investigated, follow your clinic's advice first.

If you have been trying for a while without success, sperm is only one of several possible factors. An andrological examination covers lifestyle, history and samples, and gives a better picture than single measurements at home.

• "Sauna makes you sterile." No. The effect is temporary in healthy men and reverses when the habit stops.
• "Cold showers raise testosterone." No good studies support that for healthy adults at everyday doses.
• "Cooling underwear improves your chances of having children." No studies show that for any product in the category.
• "Boxers save sperm." Underwear is one of several small factors, not a single cause.

In studies, scrotal temperature is usually measured with small sensors taped to the skin. That gives an idea of surface temperature, but not exactly the temperature inside the testis. The sensor can also come loose, move or change how the fabric sits.

Other methods include thermal cameras and measurements in a controlled room, but they work poorly in everyday life. So we know surprisingly little about how the temperature actually varies during an ordinary day, a sauna round or a night in bed.

This is one reason we are careful with firm numbers. Claims that a certain habit lowers temperature by an exact number of degrees are often based on one or two small measurements under special conditions.

The honest summary is that the direction is fairly well known, heat raises it and air and coolness lower it, but the size of the effect in everyday life is uncertain.

• If you feel a lump, swelling or heaviness in the scrotum.
• If it hurts, especially if the pain comes on suddenly.
• If you have been trying for a baby for a year without success, or six months if the woman is over 35.
• If you have questions about hormones, libido or energy that do not go away. There are many possible causes and healthcare can investigate them.