Corns can range from a slight thickening of skin to a painful, hard bump. They often form on top of buckled toe joints (hammertoes). If your toes curl under, corns may grow on the tips of the toes. You may also get a corn on the end of a toe if it rubs against your shoe. Corns can also grow between toes, often between the first and second toes.
A callus may spread across the ball of your foot. This type of callus is usually due to a problem with a metatarsal (long bone at the base of a toe, near the ball of the foot). A pinch callus may grow along the outer edge of the heel or the big toe. Some calluses press up into the foot instead of spreading on the outside. A callus may form a central core or plug of tissue where pressure is greatest.