In fact, Charles Gerba, Ph.D., a professor of environmental microbiology at the University of Arizona, told Mens Health that twenty percent of mugs carry fecal bacteria, according to the Huffington Post.
"Colonies of germs are living in your favorite cup," he told the magazine.
So, cleaning your office cup is very important, said Gerba.
He suggests bringing your favorite cup home daily to be washed in a dishwasher on the hottest temperature possible.
If you don't have a dishwasher, then first fill the cup with hot water and put a teaspoon of baking soda in it, letting it sit overnight. And then, finally wash it in hot water as you normally would, said one user on Mamapedia.