Some of it would be there anyway of course, but it's because of shoe wearing that it's so high. That's what I've read on this anyway. The interesting comparison for me is how your shoes are worse than bathroom floors. So you walk into a community bathroom, and you're still carrying that stuff hours later when you go home.

YMMV if you never walk anywhere. But for those who use communal bathrooms, walk outdoors, that kind of thing, you can pick up a lot more than mud.

Is it something to go crazy over? No, and I'm not over the top about it. I don't worry at all if guests don't take their shoes off. But after reading this research, we did change our own habits as a family about taking our own shoes off.