This is the uppermost layer of the skin which protects it from external injury. For corns and calluses, this production is the result of intermittent pressure, from shoes or weight bearing. The skin responds to this pressure by thickening. Increased mass of the lesion results in increased pressure and discomfort. A vicious cycle develops which is only broken by relieving the pressure or reducing the lesion.
Corns usually are on the toes, and result from shoe pressure.
Both terms are expressions of the same type of lesion, which is medically termed a hyperkeratosis . Both corns and calluses may have a deeper central core, known to the podiatrist as a nucleation . This can be the site of exquisite tenderness. It is simply the area of greatest pressure, often corresponding to a prominence of the underlining bone. Reducing this with sharp instruments and applying accommodative pads and tape, the podiatrist relieves discomfort and dissipates pressure.