A corn is a specially shaped callus

Callus

A callus is an especially toughened area of skin which has become relatively thick and hard in response to repeated friction, pressure, or other irritation. Rubbing that is too frequent or forceful will cause blisters rather than allow calluses to form. Since repeated contact is required, calluses...

 of dead skin that usually occurs on thin or glabrous (hairless and smooth) skin surfaces, especially on the dorsal surface of toes or fingers. They can sometimes occur on the thicker palmar

Palmar

Palmar may refer to:* a directional anatomical term of location* El Palmar de Troya, a small village near Utrera, in Andalusia, Spain* Palmar Sur , a town the Osa region, Puntarenas province, Costa Rica...

 or plantar skin surfaces. Corns form when the pressure point against the skin traces an elliptical

Ellipse

In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...

 or semi-elliptical path during the rubbing motion, the center of which is at the point of pressure, gradually widening. If there is constant stimulation of the tissue producing the corns, even after the corn is surgically removed, the skin may continue to grow as a corn.

Presentations

The hard part at the center of the corn resembles a barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

 hare, that is, a funnel with a broad raised top and a pointed bottom. Because of their shape, corns intensify the pressure at the tip and can cause deep tissue damage and ulceration. Hard corns are especially problematic for people with insensitive skin due to diabetes etc. The scientific name for a corn is heloma (plural helomata). A hard corn is called a heloma durum, while a soft corn is called a heloma molle.

The location of soft corns tends to differ from that of hard corns. Hard corns occur on dry, flat surfaces of skin. Soft corns (frequently found between adjacent toes) stay moist, keeping the surrounding skin soft. The corn's center is not soft, however, but indurated.

Diagnosis and workup

To exclude other differential diagnoses, a skin biopsy

Skin biopsy

Skin biopsy is a biopsy technique in which a skin lesion is removed and sent to the pathologist to render a microscopic diagnosis. It is usually done under local anesthetic in a physician's office, and results are often available in 4 to 10 days. It is commonly performed by dermatologists. Skin...

 may be taken. Imaging studies can be used in order to detect any underlying bony abnormalities that cause abnormal pressure on the overlying skin. For this purpose, a plain radiograph usually suffices, but, occasionally, CT scanning is used.

Treatment

Treatment of corns include paring of the lesions, which immediately reduces pain. However, if an abnormal pressure source remains, the corn generally returns. If the source of any abnormal pressure is detected, this may be avoided, such as with orthotics

Orthotics

Orthotics is a specialty within the medical field concerned with the design, manufacture and application of orthoses. An orthosis is an orthopedic device that supports or corrects the function of a limb or the torso...

and conservative footwear with extra toe space. If no other treatment is effective, surgery may be performed.