I've been aware of this idea for many years, specifically with regards to asthma. My son is 10 months old, and for his whole life, we've been pretty careful to keep him as clean as possible. It's easy to believe something in theory, but harder to make yourself do it in practice.

Growing up on a cattle ranch, I remember all my neighbor ranch kids were all as healthy as I was. Any sickly kids, that I was aware of, tended to be town kids. But, there were a lot more town kids than ranch kids, so statistically, that would have happened anyway.

It's going to be hard to even find good clean dirt and cow pies and dead deer to poke with sticks, and frogs to catch, and all the wonderful things I had to get dirty with, for my son, now that we are city slickers. We'll hike and fish, but those events don't happen every day.