A callus is a thickening of the skin that occurs in response to repeated shear or friction forces. Calluses are similar to corns, but calluses occur when abnormal forces are exerted over a larger area. Certain deformities of the feet, such as crookedness of the toes, may predispose one to the development of calluses. Calluses may cause pain, typically a burning sensation. Excessive weight-bearing and certain types of shoes are often contributing factors.

An epidemiological study performed at Johns Hopkins University looked at 784 elderly individuals to closely identify such afflictions of the foot. They found that over half had corns or calluses. Thickened toenails, cracks and fissures, maceration, and ulcers or lacerations were more common in men, whereas corns and calluses were more common in women. Women's footwear is often suggested as the reason. Increasing height of heels increases the pressure placed on the balls of the feet. Bunions are reported to have been undetected in Japan before the introduction of Western footwear. Individuals of African descent had a significantly higher prevalence of corns and calluses followed by non-Hispanic white individuals, and finally Puerto Rican individuals. This could be secondary to different rates of chronic conditions such as vascular disease, diabetes (diabetic neuropathy), obesity, and footwear styles.