When there is excessive pressure or friction on the skin, calluses and corns form to protect the skin and the structures beneath it. Calluses on the feet can develop into corns.
Calluses usually develop on the soles of the feet, on the parts that bear most of the pressure when you walk and stand. A callus, when it thickens, can cause added pressure inside a shoe against the skin.
Walking barefoot can cause thick calluses under the soles, but if someone develops calluses even if they wear shoes most of the time, it is a sign that there is an underlying problem (such as bunions or flat feet) which is causing pressure between the skin and the bone underneath it.
Shoes with high heels or narrow toes can also cause calluses – the former because the shape of the shoe shifts the body weight onto the front metatarsal bones and the latter because the narrow shape of the shoe leave little space for the toes, which are then squeezed together, causing friction.
Calluses can sometimes become infected, which may require antibiotic treatment. An X-ray can detect whether there may be an underlying bony foot structure which may be causing the problems.
Conditions for corns may be ripe when bones of the foot press against the shoe or when two feet bones press together. Often corns develop a core, which is often referred to as the "root" by patients. Corns can be very painful, especially if there is inflammation and swelling around the corn.
Common sites for corns and calluses are on the big toe and the fifth toe. There are two types of corns - hard corns and soft corns.
Soft corns can occur between the toes, especially when the ends of the toes are wider than the middle of the toes. Shoes with narrow tapering toes can also cause or aggravate these corns. Sometimes, it is sufficient for people with soft corns, to switch to wider shoes with more room between the toes. But surgery is often necessary, in which the podiatrist makes a small incision, and removes the piece of bone that is causing the problem and stitches up the toe again.
Hard corns are the most common type of corns and they are mostly formed by shoes that don't fit properly (most toes curl downward and tight-fitting shoes chafe against the the toe joints of the fourth and fifth toes) and by toe deformities. These are usually found on the tops of the toes on the outsides of the feet. This constant pressure on the toe makes the skin thicken as a protective measure – and in most instances, this actually worsens the problem.
Hard corns can sometimes be treated by changing footwear, but often, the underlying bone problem needs to be sorted out by means of surgery. Loosening the soft tissue around the bones may also allow the toe to straighten. Sometimes acid is used to burn off hard corns, but this may not be a permanent solution.
South African Podiatry Association (SAPA)