Understanding the relationship between friction and skin helps one understand how similar calluses, corns and ulcers are and what their relationships are to one another. To better understand this connection, one first has to understand the function of the human body’s largest organ – the integumentary system, a.k.a. your skin.

Depending on your source of information, the cellular turnover of the outermost layer of your body is between 40,000 cells an hour to well over a million. And irrespective of the precise number is the sense that this is an ongoing attempt to repair and renew our outermost armor.

To give a little more depth to our topic matter, I will include the dreaded blister. It may not be widely known but 15 minutes of sustained friction will most often result in a blister which is not only in acute form of a callus but at times its precursor. Take for instance the neophyte guitarist: after the first lesson, in an hour or two of practicing, the tips of her fingers become sore and after several days they form a blister. After long enough time at her craft, calluses will appear to replace the blisters.

Calluses are most often diffuse and located under softly rounded bones (think of a marble) and corns are often punctate and located over smaller bony projections (think coral reef). And soft corns are the same as ‘regular’ corns except they’re located between two contiguous bony projections, like toes and have an element of moisture.

In essence, the rate of cellular death or destruction should equal the rate of cellular birth. When there is an excess of friction sensed by your body, and overproduction of cells in the area of friction is a protective mechanism to prevent a wound from occurring. So stated another way a callus is the results of more cells being produced then being sloughed off in a very localized area.

A soft tissue ulcer is the results of a higher rate of cellular death than of its regeneration. While friction can create an area of ulceration, there are other common causes including but not limited to decreased blood supply, inadequate return and increased pressure over a bony or none bony area. And unlike most calluses or corns, ulcers are often painless. To diminish adequate perfusion of blood, which is required for normal cellular turnover, a combination of excessive pressure or inadequate blood supply can result in an ulceration just as easy as from chronic friction. Ulcers are graded, not only by their progression but by their depth.

To illustrate the influence and ease of compromised blood flow to a body part, press your index finger over an area for a few seconds and release. No matter what your blood flow or blood pressure to that body part, the pressure exerted by your finger will push all blood out of the area creating a white spot. When your finger is lifted, the blood quickly returns to the white area. This demonstrates capillary and sometimes arterial refill capability. If you were to keep your finger in place for a prolonged period of time, the area of tissue beneath your finger will be starved of blood supply and perhaps within several hours there may be signs of profound tissue death. This is what makes a tourniquet so valuable and so dangerous.

In review, a blister is an acute lesion caused by excessive friction in a short span of time. A callus is an area of an excessive amount of skin cells laid down as a result of a low-level but chronic friction mechanism most often over a diffuse area. A corn results from the same mechanism of injury but occurs over a sharp bony prominence. And finally, an ulcer occurs when more cells die than are renewed thus creating a soft tissue defect.
01.15.11
Dr. Andrew E. Schwartz
Medical/Surgical Podiatry
51 Hospital Hill Road
Sharon, CT 06069
860.364.5944

88 Elm Street
Winsted, CT 06098
860.379.3100