Cellulitis

Cellulitis is most commonly caused by Streptococcus and Staphylococcus bacteria. Streptococci Streptococcal Infections Streptococcal infections are caused by any one of several species of Streptococcus. These gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up) cause many... read more 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 Staphylococcus aureus Infections Staphylococcus aureus is the most dangerous of all of the many common staphylococcal bacteria. These gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up)... read more usually occurs around open wounds and pus-filled pockets ( skin abscesses Skin abscesses Folliculitis and skin abscesses are pus-filled pockets in the skin resulting from bacterial infection. They may be superficial or deep, affecting just hair follicles or deeper structures within... read more ).

Many other bacteria can cause cellulitis. Recently, 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 How Bacteria Shape Up)... read more ). 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 ), 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.

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 .

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 Lymphadenitis Lymphadenitis is infection of one or more lymph nodes, which usually become swollen and tender. (See also Overview of Bacterial Skin Infections.) Lymph is a fluid that oozes out of the body's... read more ), and the lymphatic vessels may become inflamed ( lymphangitis Lymphangitis Lymphangitis is infection of one or more lymphatic vessels, usually caused by streptococci. (See also Overview of Bacterial Skin Infections.) Lymph is a fluid that oozes out of the body's tiniest... read more ).

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 Deep Vein Thrombosis (DVT) Thrombosis is when a blood clot (called a thrombus) blocks a blood vessel. Deep vein thrombosis (DVT) is when a blood clot forms inside a large vein. Usually the vein is deep in your leg, but... read more ) because the symptoms of these disorders are similar.

Most cellulitis resolves quickly with antibiotic therapy. Occasionally, people develop skin abscesses Skin abscesses Folliculitis and skin abscesses are pus-filled pockets in the skin resulting from bacterial infection. They may be superficial or deep, affecting just hair follicles or deeper structures within... read more . Serious but rare complications include severe skin infections that rapidly destroy tissue (called necrotizing skin infections Necrotizing Skin Infections Necrotizing skin infections, including necrotizing cellulitis and necrotizing fasciitis, are severe forms of cellulitis characterized by death of infected skin and tissues (necrosis). The infected... read more ) and spread of bacteria through the blood ( bacteremia Bacteremia Bacteremia is the presence of bacteria in the bloodstream. Bacteremia may result from ordinary activities (such as vigorous toothbrushing), dental or medical procedures, or from infections ... read more ).

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 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 , obesity, damage to leg veins that prevents blood from flowing normally ( venous insufficiency Chronic Venous Insufficiency and Postphlebitic Syndrome Chronic venous insufficiency is damage to leg veins that prevents blood from flowing normally. Postphlebitic syndrome is chronic venous insufficiency that results from a blood clot in the veins... read more ), swelling Swelling Swelling is due to excess fluid in the tissues. The fluid is predominantly water. Swelling may be widespread or confined to a single limb or part of a limb. Swelling is often in the feet and... read more (edema), and atopic dermatitis Atopic Dermatitis (Eczema) Atopic dermatitis (commonly referred to as eczema) is chronic, itchy inflammation of the upper layers of the skin that often develops in people who have hay fever or asthma and in people who... read more (eczema). These disorders should be identified and treated to decrease the likelihood of cellulitis developing again.

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 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 ) 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 Skin abscesses Folliculitis and skin abscesses are pus-filled pockets in the skin resulting from bacterial infection. They may be superficial or deep, affecting just hair follicles or deeper structures within... read more are cut open and drained.

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