A corn or a callus is a growth of hard or thick skin, usually over a prominent area on the foot or on the bottom of the foot as a result of excessive pressures or weight in a specific area. Corns are usually found on the top of or in between the toes, whereas calluses are generally found on the sole of the foot.
A corn is usually caused by shoe pressure against a portion of a toe and usually appears on the top of the toe knuckle. It can also appear in between toes due to tight-fitting shoes and pressure irritation to the skin. Calluses are on the bottom of the feet due to excessive pressures or weight in a specific area. Faulty foot biomechanics can often be a cause in callus formation.
Wear a (non-medicated) pad over the corn to reduce friction on the inside of your shoes. If you think over-pronation is the cause, try a custom orthotic, which will reduce the excessive pronation and minimize the future growth, or return of the callus. Shoes with a deep toe box and proper cushioning will often help relieve symptoms. Severely painful corns often require surgical correction.
The most important measure that you can take is to make sure that your shoes fit properly and provide adequate room, support and cushioning for your feet.
None, unless they have become too painful.