Heads up: The dirtiest thing on your bed is your pillow.

Indeed, more than your sheets, your comforter, or your dog—no matter how ancient and grime-crusted any of those may be—your cushy midnight crown is a veritable minefield of bacteria. In fact, researchers at the University of Manchester have found that the average pillow can contain up to 16 different species of fungal spores, including aspergillus fumigatus, a common fungi that can cause serious respiratory infections in folks with immunodeficiency. Even more frightening: The researchers revealed that each pillow can contain a million individual spores—or more.

So, with all that in mind, the obvious first-step solution is to wash your pillow. Frequently. And in between washes, to keep your pillow relatively fungus-free, you should consider picking up a set of pillow protectors. Amazon sells a machine-washable four-pack for $20, but everyone from Bed Bath & Beyond to your local mattress store stocks them, too.

But the most surefire way to banish fungal pathogens for good is to banish their home: Your pillow.

In fact, the National Sleep Foundation recommends that you swap your pillow out every two years. In addition to keeping you safe from fungi and disease, picking up a new pillow will work wonders on any neck or back problems you may have. By the two-year mark, your pillow—even if it’s constructed from the world’s firmest memory foam—has certainly gone flat. A flat pillow means, no matter what your sleep position, that your spine is curved into an unnatural position, night after night after night. You can imagine all the issues that may cause.