These corns are greyish-white and soft to palpation and have a slightly sour odor. They are caused by the overriding of adjacent phalanges or by the apposition of phalangeal condyles by narrow shoes. Like calluses, corns form as a response to friction and pressure. Unlike calluses, corns have no papillary ridges, and the surface is burnished smooth because the skin responds to pinpoint pressure against a bony prominence by a rapid increase in cell production. This causes the development of layers of immature cells that never form a competent dead-skin layer as in a callus.
Corns are tender on direct pressure.
Factors that contribute to corn formation include structural problems such as osteoarthritis, hammertoe, pes cavus, and hallux valgus. Corns on the dorsa of the toes and on the lateral side of the fifth toe are aggravated by tight-fitting shoes. The treatment of most corns consists of decreasing the size of the hyperkeratotic growth and relieving or eliminating pressure on the affected area of the foot. Once or twice a week, the white, dead superficial tissue should be pared away with a pumice stone, nail file, or other debriding instrument. Patients should be carefully instructed to stop applying the keratolytic agent in the event of irritation or tenderness and to scrape away only nonsensitive tissue.