Cellulitis is a common bacterial infection affecting the deeper layers of the skin and subcutaneous tissue.

What causes it?

Similar to impetigo, cellulitis is usually caused by Staphylococcus aureus and Streptococcus pyogenes. However, the infection occurs deeper than impetigo which is a superficial infection. As with impetigo, it usually starts at sites of trauma or where the skin is broken down (e.g. due to fungal infection).  

What does it look like?

Cellulitis is characterized by redness, swelling, warmth and pain. It can occur anywhere, but the extremities are the most common site and it is nearly always unilateral. The area of redness is usually poorly defined and expands while the disease is active. There may be systemic symptoms such as fever/chills and malaise; white blood cells are often elevated.   

How is it treated?

Oral antibiotics targeting S. aureus and S. pyogenes are the treatment of choice (cephalexin, erythromycin, cloxacillin, etc.). If patients have systemic symptoms or there is concern about sepsis, IV antibiotics may be necessary. If MRSA is a concern, appropriate antibiotics should be utilized as above.