There are two types of people in this world: those who regularly wash their office coffee mug, and those who only take it off their desk to cover up the crusted coffee stain at the bottom with a fresh pour, chasing away their shame with the reasoning that the heat must kill the germs or something.
Depending on which type of person you are, this will be either mildly annoying or more-than-mildly exciting: As Heidi Mitchell wrote in a recent Wall Street Journal column, it’s fine to never wash your mug, as long as you’re not sharing it with anybody else. Better than fine, in fact: It may actually be the most sanitary option.
There are two caveats to that statement, infectious-disease expert Jeffrey Starke, a pediatrics professor at Baylor College of Medicine, told Mitchell: One, it only applies if you’re not sharing the mug with anybody else. And two, “if you leave cream or sugar in your mug over the weekend, that can certainly cause mold to grow” — in which case, wash it out.
Otherwise, though, there’s not really much to worry about: “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.” Even if you drink from it while sick, it’s pretty hard to re-infect yourself with the same mug; most viruses don’t live long outside the body.
Which means that just letting your mug live in its own filth may be a safer bet than the alternative: scrubbing it with the disgusting communal sponge in the office kitchen. “The sponge in the break room probably has the highest bacteria count of anything in the office,” Starke said. If the idea of not washing horrifies you, just stick the sponge in the microwave before using. Otherwise, though, feel free to continue your lazy ways without guilt.