This is how often you should wash your sheets, according to science Your bed is a stinking mess, In fact, it’s mind-bogglingly disgusting in there, according to Philip Tierno of the New York University School of Medicine. Here’s an edited list of what you’re sleeping on: fungi, bacteria, soil, sweat, sputum, vaginal juice, poo, urine, skin. Oh, and around 100 litres of sweat a year. Plus bits of all the snacks you’ve eaten. Hence, you’re basically sitting on top of a mega-city of bacteria and dust mites, thriving in all your horrible secretions. How often do you wash your sheets? To avoid allergies, you should be washing the filth off your sheets around once a week, Tierno says. Tierno says, ‘Stuff like that accumulates to become significant usually between one or two weeks. ‘Bottom line, they should be washed probably on the average of once a week.’