Any simple thickening of skin on the top or the bottom of the foot is known medically as a hyperkeratosis. Callouses and corns fit this definition, but the wart (veruca) does not. As mentioned above in the section on warts, this lesion is caused by a virus. Corns occur on the tops of toes and callouses occur on the bottoms of the feet. Small callouses may occur where a sweat gland dies, causing a "porokeratosis."

A podiatrist will frequently rebalance the foot, advise shoe gear changes, and debride or shave the thickened skin lesions. Acid treatment should be avoided by consumers, despite the overwhelming number of products, as adjacent tissues may become injured by the chemical. Callouses and corns occur over areas of friction and pressure at bony prominences.