The bad news: in all likelihood they're absolutely covered in tiny bugs, which could potentially include bacteria and viruses such as parainfluenza, E. coli, C. difficile and drug-resistant MRSA. If you share the device, or commonly let others use it, the danger of it harbouring some scary germs is even higher.
The good news: there's no real reason for concern, especially if you've developed good hand-washing habits. The odds of getting sick from the bacteria and viruses that linger on computers and gadgets — even those stationed in the public and used by many grubby-handed people — are about as miniscule as the tiny organisms themselves, says Dr. Alison McGeer, an infectious disease specialist at Toronto's Mount Sinai Hospital.
When asked about the chances of getting sick from using a computer keyboard in a public library, she said: "Zero. Very close to non-existent."
Still, learning about what lingers on our digital toys and tools can be plenty unnerving.
According to a 2008 study co-authored by Charles Gerba at the University of Arizona, viruses and bacteria on computer equipment typically thrive in high numbers, even though people have been conditioned to regularly use sanitizing wipes and sprays.
Computers at home were found to be far germier than the equipment at offices.
"Particularly the keyboard keys you touch the most — the E, S, T — are the heavily most contaminated, and of course the return and space bar," Gerba says.
Last year, the London School of Hygiene reported that 92 per cent of the phones they tested in an experiment were contaminated with bacteria, and 18 per cent came back positive for fecal bacteria.
Gerba has done similar research on digital touchscreens in hospitals and supermarket self-service checkout lanes. Despite the presence of so many sick people, hospitals fared relatively well, largely because of rigorous infection control policies. But the supermarket screens were found to be filthy.
"I don't think anyone really ever disinfects a touchscreen in supermarkets because you might as well stick your hand in a toilet, you'd probably get fewer bacteria on it," says Gerba.
Still, there's no need to completely avoid the self-checkout section, says McGeer. There's nothing to fear about touching those dirty surfaces — as long as you wash your hands diligently.
Bacteria and viruses are omnipresent, always within reach, so avoiding them entirely is impossible. Getting germs on your hands isn't necessarily a problem, as long as they don't find their way in your body.
"The bacteria or viruses on your fingers don't do any harm at all, it's only if they get into your mouth or around your eyes or through cuts that they pose a risk. So when you kind of multiply that out, the risk of transmission from the environment around you is really low, the big risk of transmission is other people," says McGeer, adding that you're better off trying to avoid running into someone's sneeze or cough.
"Pretty much all infection, any pathogenic bacteria or virus comes from somebody."
McGeer's advice even applies to the dirty surfaces people have long feared touching, including elevator buttons.
"If I had a nickel for everybody who said to me that we could fix infections in hospitals if we cleaned elevator buttons I would be a rich woman — the elevator buttons are not the problem," McGeer explained.
"It's not touching the elevator button, or the keyboard, or the subway poles. If you wash your hands regularly, if you don't touch your mouth with your hands, that's much more important than worrying about cleaning the environment."
Even if those germs aren't inherently hazardous to your health, it still makes sense to clean the surfaces you frequently touch. Keyboards and mice can be cleaned with a disinfecting wipe, while smartphone and tablet manufacturers recommend using a damp lint-free cloth on the glass surfaces.
And give your keyboard a good shake.
"Turn your keyboard over sometime, you'll be amazed at what comes out of it," Gerba says.
"If you turn a keyboard over in New York City you get a bagel flake snowstorm."