It’s the end of a long day, and all you want to do is prop your feet up and do a little binge-watching. Before you do, make sure to take off your shoes. Read on, because this is about way more than keeping dirt off of your clean carpet.

We know that dirt is, well, dirty. Considering all that our shoes come into contact with, it’s no surprise that we track a lot of it into our homes. When dirt winds up on our floors, it can leave stains and spread onto everything else. So sure, that’s reason number one to remove your shoes when you come indoors.

Dirt is an obvious, visible problem. But you can’t even see the scariest stuff that your shoes track in! According to a study done by researchers at the University of Arizona, there’s an astounding 421,000 different bacteria on the average pair of shoes.

Some of those types, like E. coli, are ones that can make us very sick, so this is definitely something for us to think about. If you associate E. coli and other harmful bacteria with things like improperly cooked food, you might be wondering how they wind up on our shoes, and eventually on our floor. After all, it’s not like we walk through raw hamburger!

That may be true, but think about all the things your shoes could come into contact with everyday: bird droppings, pet waste, someone’s spit, and countless other nasty things! Even if you don’t actually walk through these things, you might walk on a spot where they were. Any bacteria they carried could have been transferred to the sidewalk or street, then picked up by your shoes.

All that bacteria can really linger, this study shows. Once they’re on your shoes, the germs can be carried long distances. Bacteria from that unidentifiable goo you stepped in outside the bank can easily wind up on your living room floor, for instance, even if you wipe your feet so your shoes look clean.

Would you want to play on a carpet covered in E. coli? No way! So what can we do to stop this problem? One easy thing is to get in the habit of removing your shoes once you walk in the door. Leave them on a mat or carry them to another storage spot to keep them off of your floor.

Cleaning your floor regularly — even if it’s not obviously dirty — is also key to getting rid of any bacteria that still might find their way in. This goes for both carpets and other types of floors. Use a disinfectant floor cleaner, for instance, or steam clean your carpet every 6 months or so. Experts say that steam cleaning reduces bacteria, and can even extend the life of your carpet.

By the way, there’s a similar problem with smartphones. Anything you touch with your hands — and the bacteria you pick up in the process — can be passed to a touchscreen. So make sure to wash your hands and clean your screens regularly, too.

Check out the video below for more information on what the researchers found lurking on our shoes, as well as some tips for taking care of the bacteria problem. One thing’s for sure: We’ll think twice about wearing our shoes inside now!