Whether your pillows are natural or synthetic, they will certainly attract tiny allergy-causing dust mites, which feed on dead skin and thrive in warm, humid environments. That's a good enough reason to launder pillowcases regularly in hot water. However, you might want to take an additional precautionary step and consider getting a "pillow protector" designed to create a sealed barrier between your scalp and your pillow. Many sleep experts also remind us that pillows lose their qualities over time. So, if your pillows clump or bunch up or need constant fluffing or reshaping, they probably should be replaced or cleaned. Most pillows are washable (feathers included), but they must be fully dried to avoid mold or mildew.