Erysipelas, also known as St. Anthony's fire, is a skin infection, usually affecting the face, caused by certain types of streptococcus. Erysipelas is common in infancy and middle age. Erythema and swelling spread with a clear margin and cause blistering. It is a short illness with fever; if it affects the trunk it may however cause prostration and can prove fatal. Penicillin is the antibiotic of choice.