A Callus (or callous) is an especially toughened area of skin which has become relatively thick and hard as a response to repeated contact or pressure. Since repeated contact is required, calluses are most often found on hands or feet.
Corns (also called clavi) are specially-shaped calluses that usually occur on thin or glabrous (hairless and smooth) skin surfaces, especially on the top of toes or fingers. They can sometimes occur on the thicker palmar or plantar skin surfaces. Corns form when the pressure point against the skin traces an elliptical or semi-elliptical path. This forms a swirl of tissue, the center of which is at the point of pressure, gradually widening. If there is constant stimulation of the tissues producing the corns, even after the corn is removed or the pressure surgically removed, the skin may continue to grow as a corn.
The name callum comes from its appearance under the microscope. The hard part at the center of the corn resembles a barley hare, that is, a funnel with a broad raised top and a pointed bottom. "Corn" used to be a generic term for grain, and the name stuck. The scientific name is heloma. Hard corns are called heloma durum, while soft corns are called heloma molle.
The place of occurrence differentiates between soft and hard corns. Hard corns occur on dry, flat surfaces of skin. Soft corns (frequently found between two toes) stay moist, keeping the surrounding skin soft. The corn's center is not soft, however.
A common method is to shave the calluses down, and perhaps pad them. For calluses on the feet an inexpensive home remedy is to dissolve a foot soap powder composed of borax, iodine and bran in warm water and soak the feet in the water for 15 to 20 minutes. This softens the calluses so that layers of dead skin can be rubbed away with a cloth towel. Repeated soaking over a period of several days can often allow removal of even the core with nothing more than the friction of the cloth towel. If this fails, 40 grit sandpaper can also remove the skin.
Most corns and calluses located under the foot are caused by the pressure of the foot's bones pressing against the skin, possibly preventing it from moving with the shoe or the ground. While well-fitting shoes will help some of these problems, occasionally some other degree of intervention is required to completely rid the foot of the problem. The most basic treatment is to put a friction-reducing insole or material into the shoe, or against the foot. In some cases, this will reduce the painfulness without actually making the callus go away.
In many situations, a change in the function of the foot by use of an orthotic device is required. This reduces friction and pressure, allowing the skin to rest and to stop forming protective skin coverings.
At other times, surgical correction of the pressure is needed.