Is your laptop cooking your testicles?

Whoever invented the 'laptop' probably didn't worry too much about male reproductive health.

Turns out, unsurprisingly, that sitting with a computer on your lap will crank up the temperature of your nether regions, which could affect sperm quality.

And there is little you can do about it, according to the authors of a study out today in the journal Fertility and Sterility, short of putting your laptop on a desk.

The researchers hooked thermometers to the scrotums of 29 young men who were balancing a laptop on their knees. They found that even with a lap pad under the computer, the men's scrotums overheated quickly.

"Millions and millions of men are using laptops now, especially those in the reproductive age range," said Dr. Yefim Sheynkin, a urologist at the State University of New York at Stony Brook, who led the new study.

"Within 10 or 15 minutes their scrotal temperature is already above what we consider safe, but they don't feel it," he added.

So far, no studies have actually tested how laptops impact men's fertility, said Sheynkin, and there is no bulletproof evidence that it would. But earlier research has shown that warming the scrotum more than one degree Celsius (1.8 degrees Fahrenheit) is enough to damage sperm.

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.

"I wouldn't say that if someone starts to use laptops they will become infertile," Sheynkin told Reuters Health. But frequent use might contribute to reproductive problems, he said, because "the scrotum doesn't have time to cool down."

According to the American Urological Association, nearly one in six couples in the US have trouble conceiving a baby, and about half the time the man is at the root of the problem.

Both general health and lifestyle factors such as nutrition and drug use can influence reproductive health.

However, Sheynkin said tight jeans and briefs are generally not considered a risk factor.

"Clothes should not significantly change scrotal temperature, because you are moving around," he said.

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.

A lap pad kept the computer cool and also made sure less heat was transmitted to the skin. But it didn't do much to cool the testicles, and might give "a false sense of security," according to Sheynkin.

"It doesn't matter what pad you use," he said. "You can put a pillow beneath your computer and it still won't protect you."