Streptococcus pyogenes (beta-hemolytic group A streptococci) is the most common causative organism. Other bacteria less commonly associated with erysipelas are non–group A streptococci (groups G, C, and B) and, rarely, staphylococci. The infection enters a break in the skin barrier, such as with a surgical incision, psoriatic lesions, trauma, stasis ulcer, insect bites, or eczema. Risk factors include an impaired immune system or lymphatic system, diabetes, alcoholism, nephritic syndrome, recent streptococcal pharyngitis, and arteriovenous insufficiency.

Infection may spread to other areas of the body via the lymphatic system within the dermis, causing septic arthritis, endocarditis, and septic shock. Recurrence may cause disfigurement, and lymphatic destruction may cause elephantiasis. Other complications include abscess, thrombophlebitis, and gangrene. Acute glomerulonephritis, endocarditis, and toxic shock syndrome may also occur, but these are rare. Untreated lesions on the trunk, arms, or legs may involve large body areas and lead to death.