Your cellphone’s screen might look clean, but it’s likely crawling with germs. And this photo is proof! It was taken by a group of biology students at the University of Surrey in England. They wanted to find out what microbes were living on their devices. So they pressed the phones onto petri dishes—plates filled with nutrients that promote bacterial growth. After a few days, the dishes were blooming with bacteria. In some cases, the growth was so abundant you could clearly see the outline of a phone (left).
When you touch something, your hands pick up microbes. You transfer these organisms to other surfaces. “The bacteria on our phones show where we’ve been,” says James Meadow, an ecologist in California. “The photo seems kind of gross,” he says, “but most of the bacteria are good bacteria.”
Still, the students did find some pathogens, or harmful germs. One was Staphylococcus aureus, which is on your skin right now. While S. aureus doesn’t normally cause problems for people, the bacteria can enter cuts and cause skin infections. They can also cause respiratory illness if a person with a weakened disease-fighting immune system inhales them into their lungs.
Meadow says that there’s probably no need to clean your phone every day. We naturally have a collection of microbes living on our bodies all the time. “[The project] really just shows that, for better or worse, your smartphone is like your own personal signature,” he says.