With normal usage, bed linens should be washed once per week. However, many people fall short of that, with some going as long as four weeks without washing their sheets.
Washing sheets once per week helps ensure they remain relatively germ-, dirt-, and dust-free. People with oily skin or those who sweat at night may need to wash their sheets more often. Sheets should always be changed immediately after the occupant of the bed has been sick. Washing sheets too often, however, may result in premature breakdown of the fibers. Unless circumstances, such as bed wetting, exist, bed linens should not be changed more than once per week.
Sheets and pillowcases should be washed in warm water. Those with lace and other delicate fabrics should be washed according to the manufacturer's instructions.