Corns and calluses are patches of thick skin caused by continual pressure or friction on the area. The irritation causes the skin to die and gradually build up into a hard, protective surface.
Calluses can be just about any size, and are often irregularly shaped and either white or yellowish in color. Due to their thickness, they are usually less sensitive to touch than the rest of the skin. They often form on the bottom of the foot, which takes the most pressure when walking.
Corns are usually smaller with a clearly-defined, round shape. They tend to form on upper portions of the foot that bear less weight. Hard corns have a distinct hard center, which might be surrounded by inflamed skin. They may be grayish with a yellowed center. Soft corns are formed when a hard corn is exposed to moisture (usually sweat) for long enough to soften. They tend to be whitish in color and rubbery in texture, or may even look like an open sore. They often form between the toes.
Foot corns and calluses are usually caused by pressure from improperly-fitted footwear (whether too tight or too loose), by repeated friction or pressure from sports (runners, for instance, often develop calluses on the bottom of their feet), or from frequently walking about barefooted.
They can also form due to irregularities on the feet, such as bunions, hammertoes, or the bumps caused by rheumatoid arthritis; by an irregularity in bone structure like flat feet or bone spurs; or from pressure caused by an odd pattern of walking (abnormal gait).
Corns and calluses are generally not painful, though an inflamed or soft corn might cause some pain if pressed. They may also cause discomfort if they cause your feet to no longer fit your shoe.
Most corns and calluses can be treated from home. Try soaking your feet in warm water for five to ten minutes and then scraping the affected area with a pumice stone to remove the buildup of extra skin. Using moisturizer on the feet regularly can also help. Make sure your shoes are properly fitted to your feet and are properly designed for your activities (running shoes for running, etc.). Be sure to wear socks with your shoes. If the affected area is between your toes, a foam or silicone wedge between your toes might relieve the pressure.
If the corn or callus is very painful, or if you have diabetes, fragile skin, or circulatory problems, it is best to consult your podiatrist, who may recommend further treatment.