Cellulitis. View of swelling and inflammation on the lower leg (calf) due to cellulitis. The skin is red, taut & papery. Cellulitis is a bacterial infection of the skin & the tissues beneath it. Cellulitis is often due to infection by Streptoco- ccus bacteria entering through a wound or break in the skin. The face, neck or legs are the most common sites. Untreated cellulitis may result in septicaemia or gangrene. Cellulitis is usually treated with penicillin or erythromycin antibiotic drugs, that may have to be taken for 2 weeks. People with immunodeficiency disorders or diabetes are more vulnerable to this type of infection.