A callus is an area of skin that has been subject to degree friction and is protecting itself by a build-up of dry dead skin cells. A callus is most commonly found on the heels of the foot, the ‘ball’ of the foot, the side of the big and little toes, and at the side wall of some fingers. It can be carefully and gently removed using an abrasive or an alkaline product that breaks the bonds between the dead skin cells.