Heat and sperm: what the studies actually say

If you use the sauna often, you have probably heard that heat affects sperm production. That is true, and it is not controversial. What is less known is how thin the evidence gets when you move from the principle to the sauna specifically.

The most cited study followed ten healthy men who sat for 15 minutes, twice a week, for three months. Sperm count and motility dropped measurably during the period and normalised only after about six months.

Ten people is few. The study was not blinded, and it did not measure outcomes like pregnancies. It shows a direction, not an effect size you can plan around.

Our conclusion: the question deserves to be taken seriously without being dramatised. We still use the sauna every day. We just keep one area cooler while we do.