This Publication Is Searchable The Merck Manual of Diagnosis and Therapy Section 10. Dermatologic Disorders Chapter 121. Calluses and corns are caused by pressure or friction, usually over a bony prominence.
Corns are pea-sized or slightly larger.
Corns may be painful or tender on pressure. Diagnosis A callus may be differentiated from a plantar wart or corn by trimming away the horny skin. A corn, when pared, shows a sharply outlined yellowish to tan translucent core that interrupts the normal architecture of the papillary dermis. Although difficult to eliminate, pressure on the affected surface should be reduced and redistributed, when possible. Surgery is rarely necessary.