Saunas may be great for your circulation, but not so much for your sperm count. A new study finds that heat from frequent sauna visits can lower men's sperm production, though the effect is probably temporary.

Researchers recruited a sample of 10 healthy Finnish men in their 30s, all of whom had normal sperm counts and no history of sauna use in the past year. The participants completed a three-month sauna regimen, with 15-minute sessions twice every week. Participants provided blood and semen samples at each point in the study, and scrotal temperature was recorded before and after each session.

The results showed that participants' sperm counts and concentration were lower at the end of the three-month sauna regimen, and the numbers remained low three months after the men stopped visiting the sauna. After six months, however, sperm production was restored to normal levels.

Higher temperatures interfere with sperm production, so it makes sense that regular exposure to sauna heat would lead to reduced sperm count. The participants' scrotal temperatures increased an average of 5 degrees Fahrenheit by the end of each sauna session.

"The testicles hang down from the body in men to cool them," said Dr. Andrew Kramer, a urologist at the University of Maryland Medical Center, to Livescience. If the testicles are heated by even several degrees, sperm production declines.

That explains why sperm count may also be temporarily reduced when men wear tight pants, use hot tubs frequently, or keep laptops on their laps for prolonged periods. Recent research also shows that sperm production is highest in winter, possibly due to lower temperatures.

Though the study found lower sperm production after sauna use, it's unclear how saunas affected the men's fertility. According to Livescience, a man's sperm count does not necessarily correspond to his fertility, which is measured by the shape and speed of the sperm's movement (motility). In other words, quality may be more important than quality.

Since the study was so small, and only included healthy men, it's also unclear how generalizable the findings are to all men. Dr. Kramer told Livescience that the study does not provide enough evidence to keep healthy men away from the sauna.

According to study researcher Carlo Foresta of the University of Padova in Italy, future studies could investigate the effects of saunas on men with low baseline fertility, or on sperm development in boys who have not yet gone through puberty.

The study was published in the journal Human Reproduction in February.

The takeaway: If you're a man worried about sperm health, consider keeping your testicles away from saunas (and other heated environments) for a few months.