A corn or callus is an area of hard, thickened skin on the foot that is formed in response to pressure or friction. They are part of the body's defence system to protect the underlying tissues. If the cause of pressure is not relieved, calluses can become painful. If pressure becomes concentrated in a small area, a 'hard' corn may develop. A corn has a central core.
Common sites of corn and callus formation are the ball of the foot, under the big toe, the tips and the tops of toes. 'Soft' corns may develop between the toes, where the skin is moist from sweat or inadequate drying. Sometimes, the pressure of the corn or callus may produce inflammation, which can result in acute pain, swelling and redness.
Corns and calluses may be a sign that you have an underlying foot disorder, such as a joint that is out of alignment. This is why it is important to seek professional advice rather than attempt to treat calluses or corns yourself.