Urea helps break down dead skin . . . like the skin along the side of cracks, etc.
On a crazy note, my great grandmother always told people to pee on their hands and let it dry--another way of getting/using urea. Grandma Kramer was German, lived on a farm, died in about 1975 at the age of 94. She swore by this method of making hands soft. I've never tried it, but knowing how urea works, I have no doubt it would work.