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 also can form nucleated skin lesions underneath bony prominences on the plantar surface of the foot. These areas also can be very painful.
Causes & Risk Factors for Calluses
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., plantar flexed metatarsal bones) 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 bones (usually the second, third, or fourth) is longer and therefore, more prominent to the ground, causing it to bear more weight and pressure than the first and fifth metatarsal bones. During normal walking, the first and fifth metatarsal bones shift and the pressure is localized to the heads of the second, third, and fourth metatarsal bones.
This often occurs in people who have flatfeet (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 underneath the head of the second metatarsal bone because it is bearing most of the body 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 ill-fitting shoes or socks and participating in athletic events such as running also increase the risk. Wearing shoes with extra width and depth, soft soles, and lower heels may help to prevent calluses.
Signs & Symptoms of Calluses
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. Due to an inability to heal properly, people who have diabetes should seek medical treatment for all foot abnormalities, including calluses.
Diagnosis of Calluses
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.