Tight clothes, too many hot tubs, and a computer on your lap really can harm fertility. "The testes don't like heat. That's why they're out of the body," says Dr. Thomas J. Walsh. Exposing the testicles to too much heat has been shown to temporarily reduce sperm count. So, if you are looking to have a kid, cut back on sauna time. No need to switch underwear type though – it has also been shown that this change is unlikely to make a difference.