Since you rest your head on your pillow every night, you want to make sure that it's as clean and germ-free as possible. And no, we're not just talking about the pillowcase itself. In addition to regularly cleaning your sheets and comforter, you should also be caring for your pillows, mattress, and mattress topper. Pillows, especially, should be washed at least two to three times a year (say, every four months) to prevent odor and get rid of dust mites.