An excellent post.
"Many people assume walking over lobby carpeting or the door mat
in front of your apartment would have wiped any residual
poop particles off your shoe. But think about this: if you
step in poop and take a towel and wipe it off vigorously,
is it really off? Even if it’s a wet towel, can you be
truly certain that your shoes are truly free of all fecal
This situation doesn’t just apply to dog poop. This also
applies to human phlegm, gum, dog urine, bird poop,
chemicals, car oil, pollutants, bacteria and molds and
whatever else you might find on the sidewalks of New York
City at any time of the day. How many different kinds of
germs or chemicals, organic or non-organic, are still stuck
to the bottom of your shoe when you enter your apartment?"
This post also explains why the Hygeine Hypothesis (the theory that too much cleanliness causes allergies) is not relevant when it comes to dirt on your shoes.