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Testicle Temperature: How Heat Impacts Fertility

Is heat killing your sperm? In humans, sperm production is temperature dependent with normal testicular function requiring a temperature of 2–4°C below the general body temperature. The testicles’ ability to hang lower when too warm and retreat when too cold regulates the scrotal temperature. The tissue surrounding the testicles (blood network, fat, skin) also regulates the temperature in the scrotal sack.

Numerous external factors – such as posture, clothing, lifestyle, fever and season of the year – can affect the temperature of the scrotum and may have an impact on sperm quality if prolonged.


Heat is killing your sperm

Several experimental studies show that an artificial increase in scrotum or testicle temperature can reduce both sperm count and quality [1]. This has increased the focus of researchers to understand the adverse effects of factors that may increase the scrotal temperature.

Some studies show that males in certain occupations (bakers, mechanics, drivers) have a higher risk of decreased sperm quality. This is most likely because of increased testicular temperature. Along the same lines, a study from 2014 with 336 males revealed an association between self-reported occupational heat exposure and sperm DNA quality. The main finding was that males who were exposed to high temperatures and sat for more than six hours during work showed an increased sperm DNA damage [2].


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 [3]. Importantly, removing the heat stimulation improved the sperm parameters.

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 (see figure below) [4].

Figure 1

Figure 1 shows a decline in sperm count during heat exposure in a group of men who wore a type of underwear that forced the testicles to be pushed up so they were not able to hang freely. Sperm count increased again after the participants stopped wearing the underwear on day 120 [4].

This finding is similar to a study which showed that men who wore tight underwear had a lower semen quality compared to those who wore loose underwear [5].

Keep your testicles cool

Going through the scientific literature on heat and sperm we can conclude that heat exposure is a significant risk factor for male infertility. Induced heat to the testicles can affect sperm count, motility, and even genetic material. Especially occupational work where men are repeatedly subjected to abnormal situations may, in time, lower sperm motility and concentration. A lifestyle with tight underwear, exposure to heat from hot baths or cell phones, may also pose a risk factor for male infertility. The good thing is that it seems the negative effects are reversible!

Don’t let the heat kill your sperm! To allow for proper temperature control of the scrotal area, you should avoid:

  • tight underwear and pants – swap these for looser ones.
  • sitting down for several hours at a time. Get up and get some air to the region – let your balls hang.
  • having laptops or other hot objects near the genital area for a prolonged time.
  • long spinning classes or too long bike rides.
  • long warm baths, hot tubs, and saunas.
  • storing your mobile phone in your front pants pocket near your genital area


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