The formation of calluses is caused by an accumulation of dead skin cells that harden and thicken over an area of the foot. This callus formation isthe body's defense mechanism to protect the foot against excessive pressure and friction. Calluses are normally found on the ball-of-the-foot, the heel, and/or the inside of the big toe. Some calluses have a deep seated core known as a nucleation. This particular type of callus can be especially painful to pressure. This condition is often referred to as Intractable Plantar Keratosis.
Calluses develop because of excessive pressure at a specific area of the foot. Some common causes of callus formation are high-heeled dress shoes, shoes that are too small, obesity, abnormalities in the gait cycle (walking motion), flat feet, high arched feet, bony prominences, and the loss of the fat pad on the bottom of the foot.