Cellulitis is a spreading bacterial infection of the skin and the tissues immediately beneath the skin.
This infection is most often caused by streptococci or staphylococci.
Redness, pain, and tenderness are felt over an area of skin, the skin often feels warm to the touch, and some people have a fever, chills, and other more serious symptoms.
The diagnosis is based on a doctor's evaluation and sometimes laboratory tests.
Antibiotics are needed to treat the infection.
(See also Overview of Bacterial Skin Infections.)
Causes of Cellulitis
Cellulitis is most commonly caused by Streptococcus and Staphylococcus bacteria. Streptococci spread rapidly in the skin because they produce enzymes that hinder the ability of the tissue to confine the infection. Cellulitis that is caused by staphylococci usually occurs around open wounds and pus-filled pockets (skin abscesses).
Many other bacteria can cause cellulitis. A strain of Staphylococcus that is resistant to previously effective antibiotics has become a more common cause of cellulitis. This strain is called methicillin-resistant Staphylococcus aureus (MRSA). People who are exposed in a hospital or nursing facility commonly acquire a particular strain of MRSA that may respond differently to antibiotics than other strains of MRSA that are more common outside health care facilities.
Bacteria usually enter through small breaks in the skin that result from scrapes, punctures, surgery, burns, fungal infections (such as athlete's foot), animal bites, and skin disorders. Areas of the skin that become swollen with fluid (edema) are especially vulnerable. However, cellulitis can also occur in skin that is not obviously injured.
Certain types of bacteria can cause cellulitis when skin damaged by injuries (such as cuts) is immersed in water. The type of bacteria may depend on the type of water, for example, fresh-water ponds or small lakes, hot tubs, or sea water.
People whose immune system is weakened may be susceptible to bacteria that do not usually cause infections.
Symptoms of Cellulitis
Cellulitis most commonly develops on the legs but may occur anywhere. Cellulitis usually only affects one side of the body, such as one hand or one leg.
The first symptoms of cellulitis are redness, pain, and tenderness over an area of skin. These symptoms are caused both by the bacteria themselves and by the body’s attempts to fight the infection. The infected skin becomes hot and swollen and may look slightly pitted, like an orange peel. Fluid-filled blisters, which may be small (vesicles) or large (bullae), sometimes appear on the infected skin. The borders of the affected area are not distinct, except in a form of cellulitis called erysipelas.
Most people with cellulitis feel only mildly ill. Some may have a fever, chills, rapid heart rate, headache, low blood pressure, and confusion, which usually indicate a severe infection.
As the bacterial infection spreads, nearby lymph nodes may become enlarged and tender (lymphadenitis), and the lymphatic vessels may become inflamed (lymphangitis).
Diagnosis of Cellulitis
A doctor's evaluation
Sometimes blood and tissue cultures
A doctor usually diagnoses cellulitis based on its appearance and the person's symptoms.
Laboratory identification of the bacteria from skin, blood, pus, or tissue specimens (called a culture) usually is not necessary unless a person is seriously ill or has a weakened immune system or the infection is not responding to antibiotics.
Sometimes, doctors need to do tests to differentiate cellulitis from a blood clot in the deep veins of the leg (deep vein thrombosis) because the symptoms of these disorders are similar.
Treatment of Cellulitis
Antibiotics
Treatment of disorders that would make cellulitis worse
Drainage of any abscesses
If doctors suspect methicillin-resistant Staphylococcus aureus
People with mild cellulitis may take antibiotics by mouth.
People with rapidly spreading cellulitis, high fever, or other evidence of serious infection or who have not been helped by the antibiotics taken by mouth are hospitalized and given antibiotics by vein. Also, the affected part of the body is kept immobile and elevated to help reduce swelling. Cool, wet dressings applied to the infected area may relieve discomfort.
Disorders that increase a person's risk of developing cellulitis again (for example, athlete's foot) are treated.
Symptoms of cellulitis usually disappear after a few days of antibiotic therapy. When this release occurs, the body continues to react even though the bacteria are dead. Antibiotics may be continued for up to 10 days or sometimes longer for more severe infections.
Abscesses are cut open and drained.
Compression stockings can help prevent repeat episodes of cellulitis in the legs.
Prognosis for Cellulitis
Most cellulitis resolves quickly with antibiotic therapy. Occasionally, people develop skin abscesses. Serious but rare complications include severe skin infections that rapidly destroy tissue (called necrotizing skin infections) and spread of bacteria through the blood (bacteremia).
When cellulitis affects the same site repeatedly, especially the leg, lymphatic vessels may be damaged, causing permanent swelling of the affected tissue.
Cellulitis can develop again in people who have risk factors such as athlete's foot, obesity, damage to leg veins that prevents blood from flowing normally (venous insufficiency), swelling (edema), and atopic dermatitis (eczema). These disorders should be identified and treated to decrease the likelihood of cellulitis developing again.
