There’s probably no need to wash out that stained mug. According to infectious disease experts it’s perfectly safe to refill your dirty cup provided you’re not sharing it with others. But, as you read on, you’ll see that if you wash the cup at work you probably are indirectly sharing it with others. The only caveat is if you leave cream or sugar in your mug over the weekend, that can certainly cause mold to grow.
Of course there are germs crawling all over your dirty coffee cup, but they are yours, so there’s no danger you’re going to infect yourself from the cup. And, if it’s your coffee cup at work, washing it in the office sink with a communal sponge is not a good idea because the sponge in the break room probably has the highest bacteria count of anything in the office.
What about fecal bacteria? A study published in The Journal of Dairy, Food, and Environmental Sanitation noted that 90 percent of office coffee mugs were coated with germs and 20 percent actually had fecal matter on them. Your chance of coming into contact with E. coli actually increases if your mug has been wiped down with the office dishcloth or sponge.
It’s probably not surprising that a 2012 study led by Dr. Scott Kelley of the University of California found men’s offices had significantly more bacteria than women’s. The bacteria they discovered came from skin, nasal, oral and intestinal cavities.
But, nasty fecal bacteria is found everywhere...office furniture, phones, fast food chains, public places, gym weights and even money. As one clinical professor of microbiology and pathology put it, “We are bathed, as a society, in human feces.” Usually after going to the toilet we have around 200 million bacteria per square inch on each hand and can transfer them to five more surfaces or 14 other subjects.
Bottom line...at work you’re safer not washing your cup.