Pyogenic infection of the skin characterized by the formation of adherent crusts, beneath which ulceration occurs, most commonly localized on the buttocks, thighs, and legs. The initial lesion is a vesicle or vesiculopustule with an erythematous base which is soon surmounted by a hard crust. Removal of the crust reveals an underlying saucer-shaped ulcer with raised margin. It is caused by an infection with streptococci or staphylococci, or both. Minor injuries may determine the site of the lesions.