Testicle Temperature: How Heat Impacts Fertility

heat damaging sperm

Is heat killing your sperm? Well, maybe! The optimal temperature for sperm production is actually 2–4°C below the general body temperature and our bodies are pretty well adapted for keeping things cool. Ever wondered why your testicles hang low outside of your body and have the ability to hang lower when too warm and retreat back up when things get chilly? Well, that’s why! The tissue surrounding the testicles (the blood vessels, fat, skin) also regulates the temperature in the scrotal sack to keep your swimmers happy.

But what happens when your testicles can’t chill out? Well, this is when heat damage can occur and your fertility can be impacted. So, what can you do to make sure your sperm survives the Summer? Here we’ll break down the science behind heat damage and fertility and give tips on keeping your balls cool! 

Heat and sperm health 

Firstly, let’s understand exactly how hot under the collar we should get about heat and sperm health. Several experimental studies show that an artificial increase in scrotum or testicle temperature can reduce both sperm count and quality. This has sparked interest from researchers to understand the negative impact of factors that may increase the temperature of our testicles. 

Some studies show that men in certain occupations that involve being in hotter conditions (from bakers to drivers) have a higher risk of decreased sperm quality. This is most likely because of the increased testicular temperature they experience on a daily basis. Along the same lines, a study from 2014 with 336 men revealed an association between self-reported occupational heat exposure and sperm DNA quality. The main finding was that guys who were exposed to high temperatures and sat for more than six hours during their workday showed increased sperm DNA damage. 

What does heat do to sperm concentration and motility?

In a 2015 study researchers investigated how high testicular temperatures of 40-43°C affect semen parameters. The experiment included 40 minutes of heating for two days during a 3-month period for 19 healthy men. Researchers found that increased temperature reduced sperm concentration (from 73M/ml to 42M/ml) and sperm motility (71% to 25%) to about half of the initial values. Now, these are obviously pretty dramatic figures (and in intense conditions) but it highlights that there is definitely a link between heat and sperm health. The good news is that in the study, removing the heat stimulation improved the sperm parameters – so it also shows that heat damage may be reversible.

In a similar study, five men wore specially designed underwear forcing the testicles to be pushed up for 15 hours a day for 120 days. The estimated increase on scrotal temperature for each participant was about 2°C. Sperm parameters (motility and total sperm count) decreased after three weeks and remained low until the end of the experiment. These parameters returned to normal levels 73 days after the end of the experiment – check out the figure below to see all the results of the study! 

Again, the conditions in this study may sound extreme – and the study sample small – but it does indicate something we have known for a long time – that tight underwear is not good for your fertility!

Figure 1

Figure 1 shows a decline in sperm count during heat exposure in a group of men who wore tight underwear which meant the testicles weren’t able to hang freely. Sperm count increased again after the participants stopped wearing the underwear on day 120. 

How to keep testicles cool 

These studies make it clear that our sperm cannot handle the heat! Almost all sperm parameters – from count and motility to DNA damage – are impacted when testicles are not able to stay cool. But does this mean that our fertility is at risk every time there’s a heatwave? Not exactly. 

As the studies indicate, prolonged exposure to heat is where real damage occurs. Men whose job involves either lots of hot temperatures or lots of sitting down are most at risk. But that doesn’t mean the rest of us don’t need to try and keep our crotches cool. 

Top Tips for Keeping Testicles Cool 

Go loose on the underwear
It’s clear that tight underwear is a big culprit of turning up the testicle heat. Swap tight briefs for loose boxers so your balls can hang freely. 

Keep tech away from your testicles
You must have felt the heat coming off of your laptop and phone – especially on a hot day. Keep your phone out of your front pocket and use a tray – or better yet a table – when using a laptop.

Get moving
When we sit down for a long time, the crotch area gets pretty hot! If your job involves sitting down for a long time, make sure to get up for regular walks – it will keep your balls cool and is great for your overall health too.  

But watch out for certain exercises
You know how everyone says cycling is bad for sperm health? Well it’s the heat created from working out (usually in tight lycra) in a seated position that is the problem. That doesn’t mean you can’t ever ride your bike, but if you are concerned about your fertility, maybe give endurance racing a break. You can find more info on exercise for male fertility here. 

Say no to saunas
… and hot tubs, and hot baths. We don’t want to kill your spa day vibe, but the extreme temperatures of saunas and hot tubs are no good for your sperm health. Instead try swimming in the pool or the sea – a great form of exercise and a nice, cool environment for your swimmers! 

If concerned, get your sperm tested!
Our at-home sperm test makes it easier than ever to get informed about how your swimmers are doing. The test is performed entirely at home, and you’ll be able to test for important male fertility metrics like concentration, motility and volume – check it out here.

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