corn

A corn or clavus (plural clavi or clavuses) is an often painful, cone-shaped, inwardly directed callus of dead skin that forms at a pressure point near a bone, or on a weight-bearing part of the body. When on the feet, corns can be so painful as to interfere with walking. The visible portion of the corn tends to be more-or-less round, but corns are defined by having a hard tapering root that is directed inward, and pressure on the corn pushes this root deeper into the flesh (thus the Latin meaning "nail".) Pressure corns usually occur on thin or glabrous (hairless and smooth) skin surfaces, especially on the dorsal surface of toes or fingers, but corns triggered by an acute injury (such as a thorn) may occur on the thicker skin of the palms (palmar corns) or bottom of the feet (plantar corns). Pressure corns form when chronic pressure on the skin against an underlying bone traces a usually elliptical path during the rubbing motion. The corn forms at the center of the pressure point and gradually widens and deepens. Corns from an acute injury, such as a from a thorn in the sole of the foot, may form due to the weight of the body, when the process that creates the usually evenly developing plantar callus is concentrated at the point of the healing injury, as an internal callus may be triggered by pressure on the transitional scar tissue. Once formed, the corn itself becomes the pressure point that generates the callus. Plantar corns have appearance superficially similar to plantar warts, but the cause and treatment are very different. Names The modern medical word for a corn is Greek heloma (plural helomas or helomata); Latin "clavus" is somewhat dated. Another term is tyloma 'callus' (plural tylomas or tylomata), which tends to be more common in the United States. A hard corn is called a heloma durum or clavus durus, while a soft corn is called a heloma molle or clavus mollis.