Laptop WiFi signals send off radiation that may be killing off sperm, according to a new study.

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en could be jeopardizing their future children every time they rest a WiFi-equipped laptop on their lap. New research, published in the journal Fertility and Sterility, suggests that prolonged exposure to wireless internet signals may have the nasty side effect of killing sperm. Here's what scientists found:

How was the test conducted?
Researchers placed semen samples from 29 healthy men under a laptop connected to the Internet via WiFi, then hit download. To make sure that any changes weren't the result of the heat generated by the computer, they also put a control group of sperm samples under a laptop that was on, but not wirelessly connected.

And what happened?
After four hours, 25 percent of the sperm exposed to WiFi stopped moving, and 9 percent showed DNA damage. In contrast, the control group had 14 percent stop moving, with only 3 percent of cells showing evidence of DNA damage.

Why did WiFi kill the semen?
The culprit is likely electromagnetic radiation from the WiFi signal, although we should be "cautious to infer" a direct link, says one fertility expert. While the experiment was "well conducted," sperm that's already been ejaculated is "particularly sensitive to many factors" because "they don't have the protection of other cells" once outside the body.

So what should men do?
For now, it's best to exercise caution and keep computers off the lap — last year, similar research demonstrated that the hot underside of laptops also killed off sperm cells. "So between the heat and the radiation from today's electronic devices," says Frederik Joelving at Reuters, "testicles would seem to be hard-pressed."

Sources: BBC News, Medical News Today, Reuters