Corns and calluses are thick, hardened layers of skin that develop when your skin tries to protect itself against friction and pressure. They most often develop on the feet and toes or hands and fingers. Corns can be painful when pressed. Calluses are rarely painful. They usually develop on the soles of your feet, especially under the heels or balls, on your palms, or on your knees. Calluses vary in size and shape and are often larger than corns. Corns are smaller than calluses and have a hard center surrounded by inflamed skin.