Corns and calluses
Corns and calluses are areas of hard skin on the feet caused by excessive pressure or shoes rubbing.
Corns are usually small and circular. Hard corns tend to develop on the bumpiest parts of the foot and soft corns develop between the toes where sweat keeps them moist. Calluses are wider and less well-defined and will often develop on the parts of the foot that take the most weight, such as the ball of the foot.
If they cause discomfort, corns and calluses can be treated by a podiatrist, who can cut away thickened skin. Choosing insoles or more comfortable shoes may also help.
Source: NHS choices