Here's something we've all done before: finish a cup of coffee at the end of your work day, come in the next morning, realize you never washed said mug, shrug and quickly make a new one without taking a trip to the sink. Well, while you may have shamed yourself for your gross habits, according to scientists, it's actually not all that bad. Infectious-disease expert Jeffrey Starke, told the Wall Street Journal, "if you leave cream or sugar in your mug over the weekend, that can certainly cause mold to grow." But if you're just drinking black coffee you're good. He continued “If I went and cultured the average unwashed coffee cup, of course, I’m going to find germs,” Starke said, “but remember the vast majority came from the person who used the cup.” If this still grosses you out, feel free to wash your mug as often as you'd like, just don't use the office/communal sponge at work which as he points out, is probably the grossest thing you could do.
If you ARE going to go ahead and not wash things, make sure your coffee maker isn't one of them. Not only is a dirty coffee maker a recipe for bacteria, it can also make your coffee taste really bad.