How Bad Is it to Go Weeks Without Washing Your Office Coffee Mug?

Even if you run your dishwasher nightly at home, it’s likely been a few weeks (if not months) since your office coffee mug received more than a casual rinse. But is this more than just a bad habit? According to The Wall Street Journal, your crusty cup isn't a breeding ground for harmful, disease-causing germs. In fact, washing it with a communal kitchen sponge is likely worse for you than letting your mug sit at your desk.

Organisms and bacteria can multiply inside your mug if you fill it with liquid and touch it with your lips and hands—but the good news is that these germs probably won’t make you ill. For one thing, most viruses can’t survive for more than an hour on a stationary object. Also, even if you are feeling under the weather, it’s hard to reinfect yourself with a virus you’ve already contracted.

And while sharing mugs with your coworkers likely won't make you sick, you'd be better off keeping your mug to yourself during cold and flu season.

In short, an unwashed mug probably won’t harm your health or anyone else's (unless it’s moldy, in which case you should scrub it out ASAP). But if you do decide your go-to cup is due for a wash, steer clear of the office kitchen sponge. It’s been used to clean countless dirty surfaces, and it stays wet for hours, allowing germs to thrive and multiply. “The sponge in the break room probably has the highest bacteria count of anything in the office,” Jeffrey Starke, former director of infection control at Texas Children’s Hospital, told The Wall Street Journal. Instead, wash the mug by hand using hot water and liquid soap, and dry it with a paper towel. (Or bring it home and run it through the dishwasher.)