Men who keep their mobile phones in their front pants’ pockets may be messing with their fertility, says a new study. Laboratory research in Cleveland has tentatively found that men who use cell phones frequently have lower-quality sperm cells. It’s possible, researchers say, that the heat or electromagnetic radiation emitted by cell phones caused the effect. The men most likely to experience infertility are those who use Bluetooth or headsets to talk while the phones are in their pockets. “To get an effect, I think you’ve got to have the phone very close to the sperm,” British infertility specialist Iwan Lewis-Jones tells USA Today. Researchers found that sperm start to degrade after sitting next to an active phone for just an hour.