Corns and calluses are the most common conditions on the skin of the foot. A corn which is a thickening of the outer layer of skin usually occurs on the tops of the toes. Calluses which are the same condition on the bottom of the feet are caused by sheering pressures. A severe form of callus is considered an IPK (Intractable Plantar Keratosis). These conditions are usually painful and can respond to conservative care.