Are Sperm Counts Really Lower in the Summer?

A lot changes with the seasons: the weather, your clothing choices, the foods you eat, maybe even your mood. What you might not know, however, is that your reproductive system may also display fluctuations. Most notably, men produce less sperm in the summer months.

What happens in the summer?

Part of optimizing your fertility levels involves taking steps to make sure that your reproductive system stays happy and healthy. While eating a healthy diet and exercising regularly are important, many people don’t realize that the testicles also need to stay a few degrees cooler than the rest of the body. Regular exposure to heat is a factor in decreasing overall fertility levels. In fact, when the testicles are exposed to even mildly increased temperatures, there is a significant drop in the amount of sperm ejaculated after just two to three weeks. (But don’t worry, you shouldn’t have any issues after a couple days’ vacation in a tropical location!)


Regular exposure to heat causes lower sperm counts. Make sure to take a few minutes to cool down if you’re working outside more than four hours a day.

Not only does sperm concentration decrease throughout the summer months, sperm motility, or the ability to move spontaneously and independently, also decreases during the same time period.

According to a 2016 study performed in San Antonio, Texas, men who worked at least four hours daily in the heat found that their sperm counts were 32% lower in the summer compared to the winter, on average. Thirteen men out of the 130 tested were found to have low enough sperm concentrations to put them at risk of being infertile in the summer, whereas none of them reached these levels in the winter (Levine).

The Case for Circadian Rhythms

Why is this the case? There is no doubt that semen quality varies with the seasons. Besides the summer heat, other research has suggested that these changes might be driven by our own biological clocks, reset by the length of daylight. Even after four years of living in controlled conditions, some study participants continued to display annual patterns of testicular function (Levine). The University Hospital in Zürich, Switzerland, also studied the effect of daily circadian rhythms on sperm counts and proved that semen samples collected in the early morning before 7:30 a.m. showed the highest levels of sperm concentration (Xie). Having sex in the early morning can be used to improve natural fertility. Maybe it’s time to think about it!


Continue to nurture your loving relationship throughout the summer…we promise it will be worth it!

While there are many important steps you can take to improve your fertility, it is important to remember that many there are many biological factors that are out of your control. In fact, a disproportionately lower number of children are born in the spring months around the world compared to the fall due to problems conceiving during the previous summer. Continuing to maintain your overall health, building a loving relationship with your partner, and listening to the advice of your doctor are the biggest steps you can take in your journey to become a father.



Xie, Min, et al. “Diurnal and Seasonal  Changes in Semen Quality of Men in Subfertile Partnerships.” Taylor & Francis.

Levine, Richard J. “Seasonal Variation of Semen Quality and Fertility.” Scand J Work Environ Health , vol. 25, no. 1, 1999, pp. 34–37.

Levitas, Eliahu, et al. “Seasonal Variations of Human Sperm Cells among 6455 Semen Samples: a Plausible Explanation of a Seasonal Birth Pattern.” American Journal of Obstetrics and Gynecology, vol. 208, no. 5, 2013, doi:10.1016/j.ajog.2013.02.010.

“Men Produce Less Sperm in Summer.” UPI, UPI, 5 July 1990. 

Sirucek, Stefan. “Sperm Works Best in the Winter, Study Finds.” National Geographic Society Newsroom, 14 Dec. 2017.