Corns and calluses result from thickening of the skin in areas of high pressure and friction. The medical term for the thickened skin that forms corns and calluses is hyperkeratosis. A callus refers to a more diffuse, flattened area of thick skin, while a corn is a localized area that usually has a conical or circular shape and tends to cause more pain.
The formation of hyperkeratosis strengthens the skin in areas of friction or pressure. Abnormal anatomy of the feet, such as bunions or hammer toes, can lead to corn or callus formation, as can bony prominences in the feet. Footwear that is too tight or that exerts friction at specific points can also cause skin to thicken. Abnormalities in gait or movement that result in increased pressure to specific areas can also be the cause.