Erysipelas is a bacterial skin infection involving the upper dermis that characteristically extends into the superficial cutaneous lymphatics. It is a tender, intensely erythematous, indurated plaque with a sharply demarcated border. Its well-defined margin can help differentiate it from other skin infections (eg, cellulitis). See the image below.
Erysipelas has been traced back to the Middle Ages, where it was referred to as St. Anthony’s fire, named after the Christian saint to whom those afflicted would appeal for healing. Around 1095, the Order of St. Anthony, a Roman Catholic congregation, was formed in France to care for those with the ailment. At the time, several diseases were likely grouped under this eponym, including ergotism and herpes zoster (shingles).
Historically, erysipelas occurred on the face, but cases today most often involve the legs. The group A streptococcal bacterium Streptococcus pyogenes causes most of the facial infections; although it can also cause erysipelas on the legs, an increasing percentage of lower extremity infections are now being caused by non–group A streptococci. (See Pathophysiology and Etiology.)