Causes of Calluses and Corns
Hyperkeratosis simply means thickening of the skin. This thickening occurs as a natural defense mechanism that strengthens the skin in areas of friction or excessive pressure. Abnormal anatomy of the feet, including foot deformities such as hammertoe or other toe deformities, can lead to corn or callus formation, as can bony prominences in the feet. Footwear that is too short or too tight or that exerts friction at specific points are also a common cause of skin thickening that leads to corns and calluses. Abnormalities in gait or movement that result in increased pressure to specific areas can also be the cause.

It can be hard to know why finger corns develop since they often don't appear at sites of obvious pressure or rubbing. Finger calluses may develop in response to using tools, playing musical instruments such as the guitar, or using work equipment that exerts pressure at specific sites.