Corns more often develop because of irritation caused by tight shoes. Calluses generally consist of a broad area of thickened skin; corns may have a dense knot of skin in the center, indicating where most of the pressure is. "Hard" corns generally develop on the top or sides of toes and "soft" corns in between toes.
At first, you may not notice a corn or callus. But if whatever is causing the irritation continues, the corn or callus may become larger and cause discomfort and even pain. Corns tend to grow with time unless the pressure (such as a tight shoe) is removed. If the pressure continues, a corn may become painful and eventually interfere with walking.
Corns and calluses are often painless, but those that form because of some structural problem, such as a hammertoe (a deformity that develops when tendons and ligaments in the toe contract, causing the toe to bend over and curl up - resembling a hammer) or a bone misalignment, can progress to the point of causing pain and interfering with your ability to walk. The area around both corns and calluses can also become discolored, turning brown, red, or black.