Callosities

Callus
Examples of callus found on the toe
Classification and external resources
Specialty	Dermatology
ICD-10	L84
ICD-9-CM	700
MeSH	D002145
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A callus (or callosity) is a 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 are most often found on feet because of frequent walking. Calluses are generally not harmful, but may sometimes lead to other problems, such as skin ulceration or infection.

Normally, a callus will form on any part of the skin exposed to friction over a long period of time. For example, people often develop calluses on the middle finger of their dominant hand due to writing with a pen or pencil. Another cause is from playing string instruments like the guitar or the violin; calluses will develop on the four fingers of the hand used in holding the strings down to the fingerboard, and sometimes on the fingers of the hand used for pizzicato or strumming.

Calluses are also very common on the fingers of bass guitar and double bass players who use both the pizzicato and slapping techniques. This also applies to rock climbers on almost all of their fingers. There are many activities that can result in the formation of a callus, which may even be viewed as a badge of experience and commitment to the activity. On the feet, calluses may form on the small toes due to the compression applied by tightly fitting shoes. Activities that are notorious for causing calluses include (but are not limited to) construction work, many sports, wood carving, playing musical instruments, use of a chef's knife, rock climbing, hiking, martial arts, weight training, rowing, BMXing, dancing (especially ballet), chopping wood, monkey bars and wearing high heels. Tenpin bowlers will often develop calluses on their thumbs and occasionally their middle fingers from frequent bowling. Although often found on the foot (where the most pressure and friction are applied), calluses can occur anywhere on the body as a reaction to moderate, constant "grinding" pressure. It is the natural reaction of the palmar or plantar skin. Too much friction occurring too fast for the skin to develop a protective callus will cause a blister or abrasion instead.

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Wikipedia