Wash your cotton printed bed sheets once a week to keep them in good condition. Body oils and fluids, skin cells, dust, and dirt all put strain on the fibers of your sheets. Dust mites feed on skin flakes that our bodies naturally shed, which can cause allergic reactions in people who are allergic to mites. If you have acne-prone skin, wash your bed sheets, particularly your pillowcases, more frequently. Dirt, sweat, and bacteria buildup can aggravate your skin condition.