I have the worst case of dry skin on my feet.Im actually starting to think that it isnt dry skin but something else because nothing seems to work and I dont have a problem with dry skin on any other part of my body.It is mostly on my heels and the sides of my big toe.Its like a thick layer of dry hard skin and every once in a while it will all of a sudden get like,the only way I can describe it is that its like the skin tears off in pieces and when I try to rip the pieces off,they just pull off more skin in a line.The skin on my heels also gets so dry that if I scratch them hard they will get all pokey and I can use them as a scratching board,its gross.Ive tried using one of thoe foot sander things by witchcraft and they make my skin a bit smoother but the dead skin is always there.Its gross because in the summer I dont wear shoes sometimes and so the black from the ground stays on my feet because its all just dead skin.

What causes this and what can I do?