A callus is an overgrowth of keratin, the same protein as in fingernails. Constant rubbing or pressure stimulates the growths to protect the underlying skin from further irritation. A callus is typically less sensitive to touch than the normal skin surrounding it but can be painful if it becomes infected.
There are two major types of calluses: discrete nucleated and diffuse-shearing. The first is a localized lesion with a central keratin plug. It is typically sensitive to touch and may be mistaken for a wart. Diffuse-shearing calluses usually measure over 1 centimeter across with no keratin plug and are usually painless.
Both calluses and corns appear as thick, rough areas of skin or raised, hardened bumps. Calluses develop from repeated friction, while corns arise due to bone pressure against the skin. Corns tend to be painful when pressed; calluses may or may not be. Calluses are also usually larger, flatter, and more spread out than corns.
Calluses most often develop on the bottom of the feet, on the weight-bearing, bony areas like the big toe, heel, ball, and side of the foot. They also develop on the hands where there is repeated rubbing or friction, such as the tips of fingers or hands of craftsmen, musicians, athletes, and writers.
People are more likely to develop calluses if they have structural foot deformities or medical conditions that alter the alignment of the bones in the feet, including hammertoes, arthritis, or bunions. Walking barefoot and wearing shoes without socks or ill-fitting footwear increases the likelihood of calluses. Improper posture while walking can exert excess pressure on the inner or outer edge of the foot and cause calluses, as well. Calluses are more common in people with diabetes and systemic sclerosis.
Research confirms that cigarette smoking can spur calluses. Scientists believe that nicotine causes peripheral blood vessels to constrict, decreasing blood supply to the extremities and leading to atrophy of tissue under the skin, which causes calluses. Cigarette smoke also breaks down skin elasticity, which makes the skin wrinkled, coarse, and vulnerable to keratin buildup.
Humans have walked barefoot for most of our existence, and many people around the world never don a pair of shoes. Without shoes or sandals, the soles of the feet develop thickened skin that can protect from cold, heat, and abrasion. While shoes help protect the feet and absorb impact, they can also increase the pressure and wear on leg joints. Research suggests that going without shoes or shoe padding may be better for balance because it increases sensitivity to ground conditions. Evolutionary biologists have found that callused feet can transmit tactile sensation about as well as soft skin does.
Complications from calluses are rare and usually short-lived. Untreated calluses or those that do not respond to treatment might continue to grow, causing weight redistribution or obstructing work with the hands. They could crack and become infected, especially among people with impeded blood flow who are susceptible to infections and ulcers.
Dermatologists recommend the following treatments for calluses:
Doctors recommend a variety of approaches to prevent calluses. Coverings such as felt pads, moleskin, or bandages can protect areas that rub in footwear. Some people find success with toe separators or lamb’s wool placed between the toes. Avoid tight shoes: if the toes cannot wiggle, they are likely to rub and develop calluses. Wear padded gloves or pad tool handles.
Most calluses eventually go away once the friction or pressure that created them is removed. If the cause is unclear, or if intense pain develops, consult a dermatologist or physician. Some cases may require keratolytic therapy, orthotic therapy, injection therapy, or surgery. Individuals with poor blood flow or diabetes should call a doctor before self-treating because a callus could lead to an infected open sore.
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