A callus is thickened skin on the outer layer of your skin and is generally painless. Calluses form as a defensive measure of your body to protect sensitive skin. Calluses can occur anywhere on the body from repeated friction - hands, feet, etc. (Some examples are: a violinist who develops a callus on their chin, a guitarist or weightlifter developing calluses on the hands or fingertips, a gymnast may have calluses on their feet and hands, etc.). There are discrete nucleated and diffuse-shearing calluses.