Even if your scrub you house from top to bottom every day, there might be a jungle of germs waiting just outside. In a recent study, researchers from the University of Houston found that 40 percent of doorsteps samples were contaminated with C. difficile bacteria, and so were 39 percent of shoe soles. 

Why’s that a problem? As its name suggests, C. difficile, often known as C. diff, isn’t easy to treat—several strains are resistant to antibiotics. An infection with this bug can leave you with watery diarrhea, and in some cases it even progresses to dangerous colon inflammation. 

Recent research published in the New England Journal of Medicine suggests that nearly half a million people are infected with C. diff per year, and while it’s most notorious for infecting hospital patients, about 35 percent of cases start elsewhere. 

Related: 6 Disgusting Things that Are on Your Body RIGHT NOW!

So how does C. diff end up on your porch? “Shoes are contaminated from diverse sources, and we are regularly contaminating our doorsteps by shoes,” says study author M. Jahangir Alam, Ph.D.  

Poop from various animals, including birds, is one example of the grossness your shoes lug around. That scat can carry C. diff spores, Alam says. 

Once those spores land on a surface, they can live for months. When people accidentally ingest C. diff spores, they run the risk of getting sick. 

Want to avoid tracking germs into your house—and spending way more time on the toilet than you could possibly want? The solution is simple: Take off your shoes at the door, Alam suggests.

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