Calluses are thick and hardened areas of skin that develop as a result of repeated friction, pressure or irritation on the skin. This protective response is the skin's way of preventing injury or damage to the underlying tissue. Calluses may develop on the hands from manual labor, on the feet from walking or running, or even on the fingers from playing musical instruments or video games. Certain medical conditions such as foot deformities, poor circulation, or diabetes may also increase the risk of callus development. Wearing ill-fitting shoes or participating in repetitive activities that place pressure on certain areas of the body can also cause calluses to form.