This photo is proof that although your cellphone’s screen might look clean, it’s likely crawling with germs. A group of biology students at the University of Surrey in England wanted to find out what microbes were living on their devices, so they pressed their phones onto petri dishes. After a few days, the dishes bloomed with bacteria, and in some cases, the abundant growth resembled the outline of a phone. Believe it or not, most of the bacteria on our phones are actually good for us, says James Meadow, an ecologist in California. But the researchers did find some pathogens, or harmful germs. One, Staphylococcus aureus, doesn’t usually hurt people (in fact, it could be on your skin right now), but the bacteria can sometimes cause skin infections or respiratory illness. Still, Meadow says, there’s no need to clean your phone every day. We naturally have a collection of microbes living on our bodies all the time, and although the image looks gross, the organisms probably won’t harm us. “The bacteria on our phones show where we’ve been,” he says. “[The project] really just shows that, for better or worse, your smartphone is like your own personal signature.”