Are you wearing briefs or find it sexy to wear a tight underwear? Well if you value male fertility it is time to change to a natual men fertility treatment: Nature designed to have the testicles hang out of the body for some very good reason: normal sperm production depends on a certain temperature lower than the body temperature. Tight underwear brings the testis closer to the body, which as mentioned, not favorable for the male fertility. A warm environment slows down the production of sperm. Same thing goes to hot tubs, saunas, prolonged sitting, laying your laptop on your lap and any other things that may increase the temperature within the sperm making machine area.