Skin bacterial infections come in many different forms and are a common childhood complaint.  Cellulitis is an infection of the cells of the skin most often caused by bacteria entering the skin through a cut or scratch.  Cellulitis may progress to cause an abscess, or a collection of pus under the skin.  Most cases of cellulitis are mild and respond quickly to a course of antibiotics.  Abscesses may require incision and drainage to improve healing.  In some cases, skin infections can spread to other parts of the body, either directly or through the blood stream causing severe illness.  Some cases of cellulitis deserve special attention because swelling or extension of the infection may cause significant problems (such as in the airway, eye socket or on the face).

What are the common types of skin bacterial infections?

Cellulitis - infection of the cells of the skin.  A local area of red, swollen, painful, warm skin.  Often starts at the site of a scratch, cut or other wound in the skin. 

Skin abscess - (a.k.a. - boil, furuncle) a collection of pus (blood cells, bacteria, and debris) under the skin. The area often will feel "bumped up" or mushy to the touch.  Pus may be visible draining from the area. 

Erysipelas - commonly caused by Streptococcus pyogenes.  The area is similar to cellulitis, but the edges of the wound are typically sharply delineated and slightly raised.

Impetigo - may be a yellow, crusty lesion or a shallow, open ulcer with delayed healing or even gradual enlargement.

Folliculitis - an infection of a hair follicle that may expand into cellulitis or a skin abscess.

Carbuncle - a grouping of several skin abscesses with connecting tunnels of pus under the skin.

What causes skin bacterial infections?

The most common bacterial causes of cellulitis and skin abscesses include Staphylococcus aureus and Streptococcus pyogenes.  Many other bacteria types are less common causes of skin infections.

How are skin infections diagnosed?

Most skin infections are obvious.  If an abscess is suspected, a needle or a small blade can be used to drain the area.  In some cases an ultrasound of the area can help determine if an abscess is present.  A sample of the discharge from a lesion can be tested (by bacterial culture) to determine what type of bacteria is present and also to determine which antibiotics will be effective.

How are skin bacterial infections treated?

Uncomplicated infections are treated with antibiotics such as a cephalosporin (cephalexin or Keflex).  When a resistant bacteria is suspected, another antibiotic may be required.

What is MRSA?

MRSA is methacillin resistant Staphylococcus aureus.  Once only acquired in hospitals, this resistant bacteria type is now commonly acquired outside of hospitals and is a frequent cause of skin abscesses.  In most cases, MRSA can be treated with the antibiotics clindamycin, bactrim or vancomycin.  There is concern that bacteria will become resistant to these antibiotics also (especially if antibiotics are overused or if the full course of antibiotics is not taken).

Photo 1 - CDC/ Janice Haney Carr/ Jeff Hageman, M.H.S.  2005.  Used with permission.

Photo 2 - CDC/ Bruno Coignard, M.D.; Jeff Hageman, M.H.S. 2005.  Used with permission.