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Wingfield E. Rehmus

, MD, MPH, University of British Columbia

Last full review/revision Apr 2021| Content last modified Apr 2021

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. Recently, 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.

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 indicates 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 drug therapy.

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.

Prognosis of 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.

Treatment of Cellulitis

  • Antibiotics
  • Treatment of disorders that would make cellulitis worse
  • Drainage of any abscesses

Prompt treatment with antibiotics can prevent the bacterial infection from spreading rapidly and reaching the blood and internal organs. Antibiotics that are effective against both streptococci and staphylococci (such as dicloxacillin or cephalexin) are used.

If doctors suspect methicillin-resistant Staphylococcus aureus (MRSA) infection, such as when pus is draining from under the skin or when other serious symptoms develop, treatment may include antibiotics such as trimethoprim with sulfamethoxazole, clindamycin, or doxycycline by mouth.

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 drugs 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 risk of developing cellulitis in the future (for example, athlete's foot) are treated.

Symptoms of cellulitis usually disappear after a few days of antibiotic therapy. However, cellulitis symptoms often get worse before they get better, probably because, with the death of the bacteria, substances that cause tissue damage are released. When this release occurs, the body continues to react even though the bacteria are dead. Antibiotics are continued for 10 days or longer even though the symptoms may disappear earlier.

Abscesses are cut open and drained.

Compression stockings can help prevent episodes of recurrent cellulitis of one or both legs.

FAQs for Cellulitis

What is cellulitis?

Cellulitis is a spreading bacterial infection of the skin and the tissues immediately under the skin.

Is cellulitis contagious?

Cellulitis involving the soft tissues under the skin is generally not contagious, but it can be somewhat contagious depending on what bacteria is causing the cellulitis and whether there are any blisters, fluid, or pus oozing out, which make it easier to spread.

Does cellulitis itch?

Cellulitis may itch a bit, but most people usually describe it as uncomfortable or slightly painful.

What does cellulitis look like?

Cellulitis in the skin most typically appears red, feels warm, and is tender to the touch. The skin may be slightly swollen and pitted like the skin of an orange. Sometimes there are blisters.

Is cellulitis painful?

Cellulitis is uncomfortable, but most people do not describe severe pain.

How dangerous is cellulitis infection?

The danger of cellulitis varies depending on what type of bacteria are involved, how deep the infection goes, how large the affected area is, and whether the person has any immune system disorder or other serious health problem. Generally, a small patch of cellulitis in a healthy person is not dangerous. Cellulitis that spreads widely or deeply can be life threatening.

How long does cellulitis last?

With treatment, a small patch of cellulitis in a healthy person can resolve in 5 days or so. The more severe the cellulitis and the more medical problems the person has, the longer it can take to resolve. Very severe cellulitis may last 2 weeks or more, even with treatment in the hospital.

Is cellulitis a staph infection?

Cellulitis can be a staph infection. Staph and strep (streptococcus) are the two most common causes of cellulitis.

Can cellulitis spread?

Yes, cellulitis can spread rapidly within the soft tissues under the skin depending on factors such as the type of bacteria causing it and the person's immune system.

Drugs Mentioned In This Article

Generic Name Select Brand Names
dicloxacillin No US brand name
clindamycin CLEOCIN
cephalexin KEFLEX

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