Calluses are a collection of dead skin cells that have congealed over a section of your foot. While calluses can be painful with pressure caused by walking or the shoes we wear, they are actually a form of defense not unlike armor that the body creates to alleviate damage caused by constant friction or excessive weight placement.
Calluses can be found at one time or another on just about every one and vary in severity and location, but are common on the heel, ball of the foot and along the toes. Some may never hurt at all while others can cause consistent, noticeable pain because as they grow, the create additional irritation.
Calluses can form as a result of weight being distributed unequally along the foot, as well as by the friction caused by shoes that are either unreasonably tight or allowed to move or shift while being worn. Calluses tend to also form on the feet of people who have arch problems or have gained significant weight in a short period of time.