According to the medical journal Fertility and Sterility, men who use a
laptop can experience negative effects due to the heat put off by the
computer. The condition is called scrotal hyperthermia. Even if the laptop is placed on a lap pad that is supposed to cool the personal computer, the effect of scrotal hyperthermia is still a problem. Men can prevent overheating of the scrotum if they use their laptops on a desk instead of resting it on the lap. Other means of prevention include using the laptop with legs open for 28 minutes at most. Using the laptop with legs together is not suggested for optimal reproductive health.
A study was led by Yelim Sheynkin, MD. He, along with his team, focused on 29 men who were healthy and presented with no reproductive problems before the study. The men were told to use a laptop on three separate occasions. Each session was 60 minutes in length. The first session involved using the laptop with legs closed and computer resting on the lap. The second session involved legs closed with a laptop pad between the computer and lap. The final session involved legs open at 70 degree angle with a laptop pad between the computer and lap.
Temperature of the scrotal sac was measured in each case. The first scenario caused an increase in scrotal temperature in just 11 minutes. The second in just 14 minutes and the open leg scenario in 28 minutes. The lap pad seemed to reduce heating time by just 3 minutes between scenario one and two.
Source: Yefim Sheynkin, M.D., Robert Welliver, M.D., Andrew Winer, M.D., Farshid Hajimirzaee, M.D., Hongshik Ahn, Ph.D., Kyewon Lee, M.S. Fertility and Sterility. 08 November, 2010