Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. By signing up, you confirm you are 16+, will receive newsletters and promotional content and agree to our Terms of Use and acknowledge the data practices in our Privacy Policy. You may unsubscribe at any time. Between 20 and 30 percent of Americans bite their nails, according to The Cleveland Clinic. Why? Among other reasons, nail biting “often has a self-soothing quality—in fact, it provides a sense of calm—so people may use it as a coping mechanism.” It’s also common to bite nails while bored or stressed.  Whatever the reason, you may be wondering if biting your nails is scientifically gross, so let’s explore its health impacts. (Short answer: 1000xYes, it’s gross.) Turns out your hands are dirty You know how you’re supposed to wash your hands before eating? There’s a reason for that: hands are filthy, mostly because they’re always touching everything. Biting your fingernails is worse than eating without washing your hands—you’re sticking your fingers directly into …