Warts: Warts are abnormal growths on the skin caused by a common virus. A wart found on the bottom of the foot is called a plantar wart. Warts may appear as a solitary bump on the skin (much like a small callus) or in a cluster covering large areas. Warts may or may not be painful, but without treatment may increase in size or spread. Many treatments are available including painless topical acids, oral medications, and laser or surgical removal. Over-the-counter acid medications should be avoided.