Your hands pick up germs from door handles, lift buttons, currency notes and railings, and then they go straight to your phone. From there, those germs travel back to your hands and, eventually, your face. Even if you wash your hands carefully, picking up an unclean phone undoes the effort. Once a week is a good baseline for most people. If you share your devices, use them in public places or around someone who’s unwell, it’s worth cleaning them more often.