Not so much the body but I read somewhere that our infatuation with ablutions and cleansiness have resulted in the rise of conditions such as asthma etc. The reason being a child builds up little or no "natural" resistance to pollutants, bacteria and infections.
I know when I was a child I bathed once a week whether I needed it or not. If I went out to play I wore dirty clothes and can not recall wearing deodourant until at least puberty.
The family dogs licked my face and I recall not washing my hands obligatory before every meal. To the best of my memory, I have never been ill in my life. I get one maybe two colds a year, if that, and have never had a stomach virus in my life.