Calluses

Overview

Calluses, also called keratomas or tylomas, are areas of thickened skin caused by repeated friction and pressure. They form to protect the skin and the structures beneath it from injury or damage and can develop on any part of the body. People who work with their hands often develop calluses that help protect the fingers and palms, and musicians often develop callused fingertips from playing stringed instruments.

On the feet, calluses usually develop on the sole (plantar surface), either on the heel or under the metatarsal heads (i.e., the area where the long inner bones of the toes extend into the foot). These areas typically bear most of the pressure from standing and walking. As calluses thicken, additional pressure against the skin may cause pain. Calluses on the feet can develop into foot corns.

Calluses may form on the sole of the foot, on the heel, or under the five metatarsal heads (i.e., the area where the long inner bones of the toes extend into the foot). These areas typically bear most of the pressure and friction from standing and walking. As the callus thickens, it causes additional pressure against the skin inside the shoe, resulting in pain.

Causes and Risk Factors

People who seldom wear shoes often develop a thick layer of callus along the bottom (plantar) surface of the feet. In areas of the world where people wear shoes most of the time, calluses usually indicate a structural problem (e.g., flat feet, bunions) that causes excessive pressure and friction between the skin and underlying bone.

Calluses develop under the metatarsal heads for two reasons. In some cases, one or more of the metatarsal heads (usually the first or fifth) is too low, causing it to bear more pressure than the others.

In other cases, one of the metatarsals shifts weight to those adjacent to it during walking. This often occurs in people with flat feet (pes planus) because the arch is too low and the foot is unstable. For example, the first metatarsal (connected to the big toe) may drift upward when weight is applied, causing the second metatarsal to accept extra weight. A callus may form to protect the second metatarsal, which is not capable of supporting this extra weight.

This process can occur with the other metatarsals as well, and more than one callus often forms on the foot at the same time. In some cases, a single large callus develops across the entire metatarsal pad on both feet.

Calluses also may form when an irregularity in the shoes causes friction against the skin. Narrow-toed or high-heeled shoes can cause many painful foot conditions, including calluses.

Wearing shoes with extra width and depth, soft soles, and lower heels may help to prevent calluses.

Bunions increase the risk for developing calluses on the feet. Wearing ill-fitting shoes or socks and participating in athletic events such as running also increase the risk.

Signs and Symptoms

Calluses are thickened areas of skin without distinct borders. They may be painless or may throb or burn. Complications that may indicate an infection that requires antibiotics include pus-like drainage from the callus, increased pain and swelling, and fever. People who have diabetes should seek medical treatment for all foot abnormalities, including calluses.

Diagnosis

Diagnosis is usually based on physical examination. X-rays may be used to detect abnormalities in the underlying bony structures of the feet that may be the cause of the calluses. In some cases, skin cells are removed and examined under a microscope (called a biopsy).