Calluses are areas of thick, hardened, dead skin. They form to protect the skin and structures under the skin from pressure, friction, and injury. They may look grayish or yellowish, be less sensitive to the touch than surrounding skin, and feel rough.

Calluses on the feet generally form on the ball of the foot, the heel, and the underside of the big toe. They often form where the foot and the beginning of a toe meet.