Under normal circumstances, the testicles' position outside of the body makes sure they stay a few degrees cooler than the inside of the body, which is necessary for sperm production.
Clothes should not significantly change scrotal temperature, because you are moving around.
To hold a laptop on your knees, however, you need to sit still with your legs closed. After one hour in this position, the researchers found that men's testicle temperature had risen by up to 2.5 C.
Dr. James F. Smith, a urologist at the University of California, San Francisco, cautioned that a clear impact of laptop use on fertility had still not been shown, and that it probably didn't play a big role.
Still, he added in an e-mail to Reuters Health, heating up the scrotum is likely to be bad for sperm production. He often asks patients that he sees for infertility if they use a laptop and, if so, suggests that they spread their legs periodically or place the computer on a desk.
Dr. Smith said the consequences of continued overheating of the testicles -- so-called scrotal hyperthermia -- probably weren't permanent, but might take months to go away.
