Previous studies suggested several ways that the magnetic fields might be wreaking havoc on sperm — they could be generating DNA damage by promoting more unstable oxygen compounds, or because most men carry their phones in their pants pockets, the fields, which can cause up to a 2.3°C temperature increase on the skin, could be raising the temperature of the testes enough to suppress and interfere with normal sperm production.

Exactly how much the cell phones are contributing to lower-quality sperm isn’t clear yet — the researchers note that how long the phones are kept in pockets, as well as how much EMR the phones emit (most are legally required to stay below 2.0 W/kg) are also important things to consider when figuring out an individual’s risk. But the lab-dish studies do show that sperm are affected by the exposure, and that provides enough reason to investigate the possibility that cell phones may be contributing to lower-quality sperm and potentially some cases of infertility. More good reason to keep cell phones away from your body when you’re not using them — easier in theory than in practice, however.