A callus is simply a build up of dead skin, usually distributed over a large area. Corns are also a build up of dead skin, but they are smaller and tend to be shaped like a cone, with the point facing down into the healthy skin beneath. This makes them more painful as the point digs into the foot like a thorn.
Callus is formed by pressure and friction. Footwear and the way that we walk are major contributing factors.
Corns are also caused by pressure and friction but usually develp over a bony prominence such as a spur of bone. They are more commonly found on the toes and ball of the foot.
Corns and callus should be removed by a podiatrist under sterile conditions. The process is not painful as the dead skin being removed has no nerves or blood vessels in it. A poorly skilled operator can easily go too deep, cutting the foot and potentially causing an infection.
If possible the cause of the pressure should also be removed through changes to footwear, padding, orthotic inserts, or surgery. Your podiatrist can guide you through the best course of treatment for you.