Teenagers and young men should keep their laptops off their laps because they could damage fertility, an expert said Thursday.

Laptops, which reach high internal operating temperatures, can heat up the scrotum, which could affect the quality and quantity of men’s sperm.

“The increase in scrotal temperature is significant enough to cause changes in sperm parameters,” said Dr. Yefim Sheynkin, an associate professor of urology at the State University of New York at Stony Brook.

“It is very difficult to predict how long the computer can be used safely,” he told Reuters. “It may not be at all, if the testicular temperature goes up high within a very short period of time.”

Adolescents and young men who use laptops several times a day over many years face the greatest risk. Sheynkin fears that if laptop use is not curtailed, in 15-20 years when they want to start a family the men could face problems.

“Long-term use may have a detrimental effect on their reproductive health,” he said.

Sheynkin and his team studied the impact of using a laptop on 29 healthy volunteers between the age of 21-35 by measuring scrotal temperature before and after they used a computer on their lap.

The research is reported in the journal Human Reproduction.

Even without turning the laptop on, the scrotal temperature rose by 2.1 degrees Centigrade when the young men sat with their thighs together to balance the computer on their lap.

When they switched it on the temperature rose - by 2.8 degrees C on the right side and 2.6 degrees C on the left.

“It shows that scrotal hyperthermia is produced by both special body posture and the local heating effect of laptop computers,” Sheynkin said.

A serious case of laptop burn was reported in a letter published in a medical journal two years ago after a 50-year-old man burned his penis while using a laptop balanced on his legs for an hour, despite wearing trousers and underpants.

The researchers used two different brands of computers in the study.

“All laptop computers generate significant heat due to the increasing power requirements of computer chips. New laptops with higher power requirements may produce even more heat,” Sheynkin added.

SOURCE: Human Reproduction, 2004.