Corn - is a small area of callus with a hard centre created from callus which did not have place to grow outside so grew inside. Occurs between toes, on the joint of the toe, on sole, on metatarsal heads, can be also under the nail (subungal corn). Seed corns (multiple corns) can appear anywhere on the foot, their .The reson of this is unknown.
The reason of corn grow is a concentrated pressure. Appearance can vary deppending on the place of growh, type of pressure and strenth. Long lasting corn easily can come back, specially on the plantar aspect of the foot (bottom part) because of fibrosis. Fibrosis is an increase in fibrous tissue. Arises from repeated damage and chronicity of inflamation. Soft tissue becomes addapted to presence of leasion's crater (corn in this case) and rapidly fills it with hyperkeratotic skin (hard skin), after removal, leading to another corn or only small callus growth.
To avoid corns pressure from the foot should be removed without any delay, so should hard skin or created already corn.
Another growth on the foot which can be observed also under corn is bursae (small red hill built by the skin to reduce pressure and shearing). If pressure still is applied hard skin and next corn occurs. A bursae can appear commonly on toe's joint, tendo Achilles, under the first metatarsal (hallux abductovalgus).