The summer is all about backyard grilling, relaxing on the beach and steamy summer sex. But it turns out that heat can kill sperm.
The ideal temperature for sperm production is 2-4 degrees lower than body temperature. This is why a lot of men who have jobs where they are exposed to high temperatures, like bakers and ceramic oven workers, experience infertility.
Optimal Temperature for Sperm Production
In order for men to produce healthy sperm, the testicles must remain cooler than body temperature. The human body is well-adapted to this, with a special network of blood tubes that eliminate excess heat and the scrotal sac, which contracts when temperatures are low to draw the testicles closer to the body. However, the body’s natural cooling mechanisms are not enough to prevent high temperatures from adversely affecting sperm production.
Researchers in Wuhan, China, recently analyzed semen samples from 792 men with a range of fertility issues. The team found that the quality of sperm deteriorates significantly as air temperatures rise.
This was particularly true at the key stages of sperm development, with a higher decline in concentration and a lower percentage of normal sperm morphology seen at elevated temperatures. The team also found that there was a significant interactive effect between ambient temperature and PM2.5, with higher levels of the particle being associated with more severe declines in sperm quality.
The team also noted that some men were more resilient to the effects of ambient temperature than others. In fact, they found that around 40% of the variation in the rate of decline in sperm count as temperatures increase was explained by differences between individual males. The results suggest that a personalised approach to managing the impact of climate change on sperm quality may be necessary for men who are having difficulty trying to conceive.
Temperature in the Scrotum
Testicles are located outside the body and hang in a pouch-like structure called the scrotal sac (pronounced: kr-tol-uhm). The scrotal sac helps to keep the testicles at an optimal temperature for sperm production. This is because the scrotal sac has a network of blood tubes that eliminate excess heat. The scrotal sac also moves up and down depending on the surrounding environment. This allows the testicles to hang lower in cold temperatures and higher in warm temperatures to protect sperm.
The scrotal sac has another smart feature to prevent testicular overheating. A muscle called the cremaster (pronounced: -mohrst) contracts in cold conditions to move the scrotal sac closer to the body. In hot conditions the cremaster muscle relaxes to allow the scrotal sac to hang freely away from the body to avoid overheating.
Although a short period of high testicular temperature does not affect sperm quality, long-term exposure to high temperatures may lead to a decrease in sperm production and motility. This is because repeated exposure to high testicular temperatures can cause the sperm cells to die or become abnormally shaped, leading to infertility. Therefore, men should limit the amount of time they spend in hot tubs or taking hot showers. It is also recommended that men wear loose-fitting clothing and sit with their thighs apart when possible to keep the temperature of the testicles and scrotal sac low.
Temperature in the Scrotal Bag
The scrotal bag is the home to the testicles, two small, oval-shaped male sex glands that produce testosterone and sperm. They need a temperature around 2 degrees cooler than the body, which is why the testicles are stored outside of the body in the scrotal sac.
The sac draws the testicles closer to the body for warmth when it gets cold, and moves them away from the body to lower their temperature when it’s warm. This smart adaptation helps maintain the ideal temperature for sperm production, Scientific American reported.
It’s important to keep your scrotal bag cool, since heat can affect sperm count and motility. When the scrotal bag becomes too warm, sperm may be unable to develop properly and will struggle to fertilize an egg, leading to infertility.
One of the main causes of high scrotal temperatures is sitting for long periods of time, especially in an office chair or in a car seat. Researchers found that the scrotal temperature rises by 1 degree per hour of sitting, and sperm concentration drops 40% for each scrotal temperature increment.
To keep your scrotal bag cool, avoid wearing tight underwear and spend as little time sitting as possible, especially when in a chair. Instead, try standing or walking for short periods of time. Also, be sure to wear loose pants and make an effort to sit with your legs spread when at work or while on a road trip.
Temperature in the Sperm Bank
At RMA of NY, sperm is collected via masturbation in a specialized collection device and then cryopreserved in our laboratory for storage. The sperm is stored at a temperature of -196 degrees Celsius which maintains the ability to fertilize an egg. Cryopreservation of semen can be done for a variety of reasons; a man may wish to store his sperm to use in a future IVF cycle, or he may simply choose to have a sample preserved to allow him to start a family when he is ready.
In one study, exposure to ambient air temperature was found to be negatively associated with sperm concentration, total motility, and progressive motility. Sperm concentration was found to decrease by about 5% for every degree of lower temperature exposure, while progressive motility was found to decrease by about 17% for each degree of higher temperature exposure.
A similar negative correlation between air temperature and sperm concentration was reported in another study. Similarly, the number of sperm that were normal in morphology also decreased with the increase in environmental temperature.
Individual differences in fertility traits were found to be highly significant. For example, differences in how resilient females are to changes in temperature explain 24% of variation in the rate of decline in egg laying during hot periods and 18% during colder periods. Likewise, variations between males in how resilient they are to the effects of temperature change explain around 57% of variation in the rate of decline in sperm count during hot periods and 47% during colder temperatures (Supplementary Table 1).
