Cellulitis is a skin infection characterized by redness, swelling, and pain. It is an infection of the deeper layers of the skin that is usually caused by a group A streptococcus and S. aureus in adults and Haemophilus influenzae type B in children less than 3 years of age.

The most reliable way of making a diagnosis of cellulitis is by recognizing the physical signs and symptoms, which include redness, warmth, swelling, and pain. Identifying the causative bacterial agent is difficult in most adult cases and is usually not attempted. Fever may be present. Patients with cellulitis usually have a preexisting lesion or wound.

Due to the predictability of the involved organisms, empiric treatment with antibiotics aimed at staphylococcal and streptococcal organisms is appropriate in adults. Some choices of antibiotics include penicillin, cephalosporin or erythromycin. For more severe infections, intravenous antibiotics may be necessary.

In individuals with recurrent infections, prolonged antimicrobial prophylaxis is effective and safe. This therapy may be continued for months or years. An antimicrobial agent with activity against both streptococci and staphylococci is recommended.