Long ago, I used to feel a teensy bit of shame when I was out in the garden and I'd pull up a carrot, wipe it on my pants, and then eat it even though there were remaining clumps of soil in the little grooves of the root. I felt a bit uncivilized. I've long since abandoned that shame for the not-to-be-duplicated experience of grazing straight from the garden. Turns out there may be some very good reasons not to be afraid of a little dirt.
I recently heard a brief story on "The Environment Report" about recent studies that suggest that certain bacteria found in soil not only improve immune system function, but may also be reducing anxiety and making people smarter! (Minus typos, like the one in the article's title.) There's also a Discover magazine article that gives a brief explanation of the findings.