Your pillow is far dirtier than your pillowcase: the 2-minute test your pillow probably won’t passYou wash your sheets. The Asthma and Allergy Foundation of America goes a step further for anyone with allergies, suggesting a swap every 6 months to a year. It’s dead dust mites and their droppings that have built up inside. The Mayo Clinic and the American Academy of Allergy, Asthma & Immunology both point to this temperature. ; (2) Asthma and Allergy Foundation of America, Dust Mite Allergy; (3) Live Science, Does Your Mattress Really Gain Weight Over Time?