Written by Jenny Wordsworth. Reviewed by Dr Phoebe Howells. 

Male fertility is shaped by much more than your genetics. Behavioural and lifestyle changes have daily impacts on your fertility, and with sperm taking roughly 90 days to be produced, the months leading up to trying to conceive can play a crucial role in your journey. Here we discuss how everyday habits such as hot tub use, cold plunges, alcohol, weed and nicotine can all interact to affect your reproductive health.

How hot is ‘too hot’? 

The testes sit outside of the body and are 3°C cooler than the rest of the body. This cooler environment is thought to be essential for the production of healthy sperm. The testes regulate their own temperature, contracting closer to the body when it’s cold and relaxing when it’s warm. The movement is controlled by the cremasteric muscle, which constantly works to regulate the temperature of the testes to be optimal for sperm production.

Saunas, baths, hot tubs, jacuzzis and steam rooms change that. The worst of these is anything that involves submerging the testicles underwater; they’re essentially in the hot water themselves, and therefore directly exposed to that temperature. Typically, a hot tub is 38-40°C, and within a short period of time, your testes will assume that temperature.

A 2007 study on wet heat exposure in the Brazilian Journal of Urology took 35-year-old infertile men with low sperm counts and stopped them from having hot baths ‒ semen quality went up 300%. Total MOT count (sperm motility) went up 300% in 3 to 4 months and 600% in 6 months. The main takeaway from this study is that time is needed here; that’s the recovery curve.

Therefore, let’s look into what the lethal dose to male fertility is when it comes to heat. When evaluating this, we usually refer to the LD50, which is the amount required to kill roughly 50% of the sperm present. For heat, this appears to be 20 minutes at 40°C, which approximates to the average temperature of a hot bath or jacuzzi. As a rule of thumb, it's best to avoid these if you're trying to optimise your sperm health.

We should also consider saunas and their impact. As the testes aren’t underwater whilst in a sauna, there’s no submersion to consider, but being in a hot room is going to affect them. We estimate the effect is one quarter to a third of that of a hot bath (or other form of submersion). When it comes to steam rooms and showers, these are likely fine, although for steam rooms, it likely depends on how much time you spend in one. The key takeaway is to avoid hot tubs and hot baths.

What about the cold? 

While many have stressed the benefits of cold plunges for health, there is limited research on their actual impacts on male fertility. A 2024 study analysed over 75,000 semen samples from over 30,000 donors to investigate the effects of temperature extremes on sperm quality. The findings concluded that both hot and cold temperature extremes resulted in reduced sperm quality. While these did not investigate the specific effects of brief cold plunges, it would be sensible to treat these with caution when trying to optimise male fertility. As always, balance is key.

‘Scrotal Cooling’ is the process of slightly lowering the temperature of the testes using methods such as cooling packs. This is less of a drastic change in temperature than ice baths or cold plunges. However, there is still a lack of rigorous evidence on the impact of scrotal cooling: a 2013 systematic review analysed the research available and its effects on male fertility. However, the researchers concluded that while there were positive trends in the data, these were insufficient to draw a conclusive argument supporting scrotal cooling for male fertility.  

Therefore, the jury remains out on both cooling in general and the impacts of extreme cooling on male fertility. For those trying to optimise fertility, it would be wise to avoid cold plunges and, at the very least, err on the side of caution until further research is conducted. 

This is not something you have to stop forever, but with sperm production taking roughly 90 days, we would recommend avoiding these for a few months before and whilst trying to conceive. 

How alcohol, marijuana, and nicotine affect male fertility 

Now let’s talk specifically about the effects of alcohol on fertility. For men, government guidelines recommend that adults should drink no more than 14 units of alcohol per week, ideally spread over no more than 2 to 3 units per day, with several alcohol-free days each week.

From the evidence, we know there’s a direct effect of alcohol on sperm morphology, motility, and sperm count. Alcohol is one of the few things that gets ‘into’ the testicles, as such, and it’s an important point to note as you consider whether to lower your alcohol intake when preparing to try and conceive. We also know there’s a hormonal effect of alcohol: it tends to cause the liver to ‘rev up’ oestrogenisation, so you tend to get lower testosterone as a result.

Given we know alcohol has both a hormonal effect and a direct effect, it’s best to limit alcohol intake in the 90 days leading up to first trying to conceive, and ideally on an ongoing basis too. It’s worth trialling all the alcohol-free options available today, as there’s a vast selection. 

Marijuana, specifically THC, is the worst player when it comes to impacting sperm health, where your sperm count, motility, and morphology all take a hit. We know it affects fragmentation, too, which is a quality measure of sperm. There’s evidence that it probably has an epigenetic effect too, which means there’s a heritable change in gene expression that doesn't alter the underlying DNA sequence, but instead regulates whether genes are turned on or off.

Some of the early studies on sperm epigenetics showed alterations with nicotine and with marijuana. Another issue with marijuana is that it remains in your fat deposits after consumption. So it’s not the case that you ingest it, smoke it, get the ‘buzz’, and it disappears. It remains in fat deposits for 3 weeks to a month, continuing to give out a low level of toxicity long after the initial consumption. 

For nicotine, whether in synthetic or tobacco form, it’s a bad actor at high doses when it comes to impact on sperm health. The impact doesn’t last as long as THC, but it does have effects on sperm count, motility and fertility. If you can, it’s an idea to seek support from your GP to help you give up smoking in any form.

Key Takeaways

• The impact of extreme temperatures, particularly hot extremes, is a cause of concern for sperm health and should be avoided before and while trying to conceive.

• Legal drugs, including alcohol, marijuana and nicotine, should also be avoided during this period, as they have been proven to have a lasting negative impact.

• Sperm health reflects overall wellness. Since sperm take around 90 days to mature, consistent healthy habits in the months before conception (including balanced temperature exposure, diet, sleep, and stress management) can meaningfully improve fertility outcomes.