If your pillow comes with cleaning instructions that include how often you should wash the removable cover, you should follow those instructions—but if it doesn’t, you should plan to wash your cover as often as you would your regular pillowcases or sheets. Per the Sleep Foundation, this may need to be as frequent as once a week. “Maintaining proper hygiene [and cleaning of your pillowcase] is important,” explains Dr. Brown, “to minimize the development of harmful bacteria or germs that can lead to skin irritation or other harmful conditions.”