Calluses

Causes

A wide variety of factors may lead to the development of a callus.

• Extrinsic factors include poorly fitting footwear (such as shoes that are too tight or have a small toe box), walking barefoot, thin-soled shoes, high heels, thick socks or socks with seams by the toes, prolonged standing, and repetitive activity (i.e., athletics, manual labor). Athletes develop calluses due to repetitive motion and recurrent pressure on the same spot. For instance, cyclists develop calluses on their palms from holding the handlebar grips. Rowers form calluses on several areas of the hand due to friction between the oar and the hand. Runners develop foot calluses from repetitive pounding on hard road surfaces. Dancers and gymnasts develop calluses on their feet from distinctive weight-bearing positions. Wrestlers can have knee calluses from pressure exerted on the mat. Surfers who paddle on their knees develop large, calcified calluses (“surf knots”) on their knees.
• Intrinsic factors include foot deformities (high-arched feet, claw toe, hammer toe, mallet toe, short first metatarsal, bunions, malalignment of the metatarsal bones, flat feet, loss of fat pad on the underside of the foot, malunion of fracture), poor foot mechanics or abnormal gait, and obesity.

Presentation

A callus presents as a broad-based, diffuse area of hard growth with relatively even thickness, usually at the ball of the foot. It lacks a distinct border. The affected skin is rough and discolored and can vary in color from white to gray-yellow or brown. Calluses are more common in women than in men.

Calluses are often painless and can actually be advantageous to some athletes. Boxers and martial artists build up calluses on their hands to become more resistant to pain from impact. Dancers develop calluses from dancing barefoot, and yet the calluses can facilitate performing turns. Although typically benign, pressure or friction can precipitate pain. Discomfort, for foot calluses specifically, is amplified by thin-soled and high-heeled shoes. Relief comes with rest.

Some calluses develop a deep-seated core known as a nucleation, and patients will complain of pain when pressure is applied. This type of callus is referred to as intractable plantar keratosis.

Making the Diagnosis

Calluses are diagnosed based on findings on clinical exam. The location and characteristics of lesions are noted, and the affected area is palpated to feel for a prominent bone underneath the skin surface. X-rays may be done to look at the underlying bony structures that may be the cause of calluses.

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