Cellulitis is an acute inflammation of the connective tissue of the skin, caused by infection with staphylococcus, streptococcus or other bacteria (see also Erysipelas).

The skin normally has many types of bacteria living on it, but intact skin is an effective barrier that keeps these bacteria from entering and growing within the body. When there is a break in the skin, however, bacteria can enter the body and grow there, causing infection and inflammation. The skin tissues in the infected area become red, hot, irritated and painful.

Cellulitis is most common on the lower legs and the arms or hands, although other areas of the body may sometimes be involved. If it involves the face (erysipelas), medical attention is urgent. People with fungal infections of the feet, who have skin cracks in the webspaces between the toes, may have cellulitis that keeps coming back, because the cracks in the skin offer an opening for bacteria.

Risk factors for cellulitis include:

• Insect bites and stings, animal bite, or human bite
• Injury or trauma with a break in the skin (skin wounds)
• History of peripheral vascular disease
• Diabetes -related or ischemic ulcers
• Cracks or peeling skin between the toes
• Use of immunosuppressive or corticosteroid medications

• Localized skin redness or inflammation that increases in size as the infection spreads
• Tight, glossy, "stretched" appearance of the skin
• Pain or tenderness of the area
• Skin lesion or rash (macule):
  • Sudden onset
  • Usually with sharp borders
  • Rapid growth within the first 24 hours
• Warmth over the area of redness
• Fever
• Other signs of infection:
  • Chills, shaking
  • Warm skin, sweating
  • Fatigue
  • Muscle aches, pains (myalgias)
  • General ill feeling (malaise)

• Nausea and vomiting
• Joint stiffness caused by swelling of the tissue over the joint
• Hair loss at the site of infection

During a physical examination, the doctor may find localized swelling. Occasionally, swollen glands (lymph nodes) can be detected near the cellulitis. Your health care provider may mark the edges of the redness with a pen, to see if the redness extends beyond the marked border over the next several days.

Tests that may be used:

• A CBC may show an elevated white blood cell count, and indicates a bacterial infection.
• A blood culture may be performed if generalized infection is suspected.