There is a grain of truth in the myth about hot tubs preventing pregnancy. Men who are trying to become dads should probably avoid frequent dips in the hot tub because the testes are very sensitive to heat. Men’s testes are outside the body for a reason — they need to be in a cooler environment to produce healthy sperm.

“Wet heat” isn’t good for the testes and, according to a study published in 2007, even 30 minutes in a Jacuzzi or hot tub can temporarily decrease sperm production.  Also, the hot water can affect the immature, developing sperm and create an incomplete genetic code, leading potentially to birth defects.

However, this study also showed that the negative effects of wet heat on sperm may be reversible. Wet heat exposure can impact a man’s sperm for a surprisingly long time. Because sperm takes so long to mature, any interventions (to reduce exposure) will usually take at least three, if not six to nine, months to show any benefit.

So a trip to the hot tub in January can impact developing sperm that’s released as late as March, even April.