Well, actually, I was told by a podiatrist once that what it is, is your body weight isn't exactly symetrical and in order for you to balance correctly your feet build up a thicker skin where needed. Over time the thick skin gets too thick and dries out, that's what callouses are, very thick skin. And because it has no blood supply it gets dried out. I have a hip displasia from birth that makes me walk unbalanced. Plus my right leg is bowed a bit more than my left. I'm ALL out of wack here. :o