Corns or calluses are hardened and thickened skin that develops in a small area which receives continuous pressure or friction. The skin hardening occurs in response to this continuous pressure or friction to protect the lower softer layers. A small area of tissue underneath the hardened portion of the skin called the bursa remains inflamed and increases the lifespan of the corn. Corns usually develop on the hands and feet, including fingers and toes, mostly in people who do a lot of walking and/or manual labor, and in those wearing ill-fitted shoes.
The most prominent cause of corn formation is ill-fitted, or old and worn out shoes. When the entire foot is encased by a shoe, pressure develops against bone formations on the foot and toes. Improper support in ill-fitting or worn out shoes causes this pressure to harden the skin to corn. Corns also develop in those who regularly walk long distances or stand for a long time without breaks. Corns on the palms and fingers are very common in manual laborers who make heavy use of a number of tools like hammers, spades, scythes, etc. Friction from these tools causes the formation of corns. Corns may also develop in certain cases where a foreign body like a thorn, prickle, etc. goes in and gets stuck in the skin and the pressure from it causes corn to form.
Mostly, corns disappear slowly once the cause of the pressure is removed. So a change of shoes will usually cure the corn. Other treatment methods include ointments, medicated plasters, or surgery.