Even if you wash your sheets, your bed is dirtier than you think: the overlooked part almost no one cleansYou strip the bed on Sunday. A year: hundreds of gallons of moisture and pounds of skin cells cycled through the same square footage of your bedroom. Dust mites are microscopic, they thrive in warm humid fabric, and they feed on the skin cells humans shed constantly. Dust mites are microscopic, they thrive in warm humid fabric, and they feed on the skin cells humans shed constantly. Sheets, mattress pad, everything.