Merck Manual

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Wingfield E. Rehmus

, MD, MPH, University of British Columbia

Reviewed/Revised Jun 2023
Topic Resources

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.

Causes of Cellulitis

Many other bacteria can cause cellulitis. A strain of Staphylococcus that is resistant to previously effective antibiotics Antibiotic resistance Bacteria are microscopic, single-celled organisms. They are among the earliest known life forms on earth. There are thousands of different kinds of bacteria, and they live in every conceivable... read more has become a more common cause of cellulitis. This strain is called methicillin-resistant Staphylococcus aureus (MRSA Methicillin-resistant Staphylococcus aureus (MRSA) Staphylococcus aureus is the most dangerous of all of the many common staphylococcal bacteria. These gram-positive, sphere-shaped (coccal) bacteria (see figure ) often cause skin infections... read more Methicillin-resistant <i > Staphylococcus aureus </i> (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 Athlete's Foot (Tinea Pedis) Athlete’s foot is a dermatophyte (fungal) infection of the skin of the feet. Symptoms of tinea pedis include a build up of scale on the feet and sometimes redness and itching. Doctors base the... read more Athlete's Foot (Tinea Pedis) ), 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 Erysipelas Erysipelas is a superficial form of skin infection ( cellulitis) typically caused by streptococci. (See also Overview of Bacterial Skin Infections.) Erysipelas is most commonly caused by Streptococcus... read more 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.

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.

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, when other serious symptoms develop, or if MRSA is a common cause of cellulitis in the community, 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 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.

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.

Compression stockings can help prevent repeat episodes of cellulitis in the legs.

Prognosis for Cellulitis

When cellulitis affects the same site repeatedly, especially the leg, lymphatic vessels may be damaged, causing permanent swelling of the affected tissue.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Biocef, Daxbia , Keflex, Keftab, Panixine
Primsol, Proloprim, TRIMPEX
Cleocin, Cleocin Ovules, Cleocin Pediatric, Cleocin T, CLIN, Clindacin ETZ, Clindacin-P, Clinda-Derm , Clindagel, ClindaMax, ClindaReach, Clindesse, Clindets, Evoclin, PledgaClin, XACIATO
Acticlate, Adoxa, Adoxa Pak, Avidoxy, Doryx, Doxal, Doxy 100, LYMEPAK, Mondoxyne NL, Monodox, Morgidox 1x, Morgidox 2x , Okebo, Oracea, Oraxyl, Periostat, TARGADOX, Vibramycin, Vibra-Tabs
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