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Last year brought us the testicle bath contraception, an ingenious device requiring the user to dip their testicles into a machine holding water at a certain temperature. Moments later, the testicles undergo a little spa session and are hit with ultrasound, suppressing spermatogenesis (basically meaning your little swimmers are not swimming any longer).

It has been known since 1977 that ultrasound is a good contraceptive. What is also known, but not often talked about, is how heat can also affect sperm. This prompts the shower (well bath) thought – if you are trying to conceive, is a long, relaxing bath good for the sperm?

Your body is normally kept at 37oC (98.6oF), which is a bit of a problem for testicles as they need to be two degrees lower to keep their function on point. The human body is a fantastic system and actually has a way around this, potentially the answer to the question "Why do testicles dangle?". The testes are covered by a muscle called cremaster, which can involuntarily contract or relax the testes toward or away from the body depending on if they need to be warmer or cooler – like a muscley accordion. 

This is critical for the continuation of the human population, as one study found that if the scrotal temperature is increased by a few degrees then this can cause infertility.

There have been a fair few studies on temperature and testicles. This has been investigated for years, as heat stress can cause lower sperm count, reduced movement and sperm concentration, and changed morphology.

It is thought that higher temperatures are associated with oxidative stress, and in turn, this can cause the DNA inside the sperm to be damaged.

For temperature in general, in one small study (and we mean small, there were 5 fertile volunteers), wore special underwear that made the testes mildly toasty for around 15 hours a day, for 120 days. Overall, it was found that this mild temperature increase led to lower sperm count, plus increasing sperm carrying an abnormal number of chromosomes. Don’t worry, 6 months after the experiment the sperm were back to their normal swimming selves.

But what about the original question about hot baths?  

One small study in 2007 looked into hot tubs, jacuzzis, and hot baths in relation to fertility. The people were involved in a three-year study, and the participants took these hot water delights for at least 30 minutes per week. The people in the study were then told to stop exposing themselves to these heat sources, and nearly half of these patients (five out of eleven) found that their motile sperm count increased by 491 percent.

A 2016 study had the participants have a lovely soak in a 43°C (109.4°F) heated bath for 30 minutes per session, for 10 times. Taking these hot baths led to sperm DNA damage and sperm cell death. As you may have also thought, a hot bath every day caused more damage than a less frequent dip every three days.

There have also been a lot of studies on the effect of saunas and sperm quality. 

A 1983 study found that even one 20- minute sauna at 85°C (185°F) could affect sperm, that the sperm count decreased after one week before returning back to normal after five weeks. In 1998, one paper described how visiting the sauna for two weeks, decreased sperm movement. A 2013 study, sent volunteers to a steamy sauna session twice a week for 3 months, each lasting 80-90°C (176-194°F) for 15 minutes. This study saw an increase in elevated testicle temperature that caused a drop in motility and sperm concentration.

A more recent 2020 study examined 1,311 participants and found that going to the sauna (along with wearing tight underwear) was related to lower semen concentration and lowers motility and morphology.

Overall, if you want a bubbly bath, laze around in a hot tub, or get the "boys" out during a sauna session while trying to conceive, you may want to put the spa session on hold at the moment. Current research suggests that there are short-term implications for sperm quality, but some studies indicate that if you put these habits on hold for a few months, they should go back to your normal sperm quality levels.

Beccy is a custom content producer who holds a PhD in Biological Science, a Master’s in Parasites and Disease Vectors, and a Bachelor’s in Human Biology and Forensic Science.

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