Corns are calluses that form on the toes because the bones push up against the shoe and put pressure on the skin. The surface layer of the skin thickens and builds up, irritating the tissues underneath. Hard corns are usually located on the top of the toe or on the side of the small toe. Soft corns resemble open sores and develop between the toes as they rub against each other. Improperly fitting shoes are a leading cause of corns. Toe deformities, such as hammertoe or claw toe, also can lead to corns.