Cellulitis (sel-u-LIE-tis) is a common, potentially serious bacterial skin infection. The affected skin appears swollen and red and is typically painful and warm to the touch.
Some bacteria are naturally present on the skin and do not usually cause harm. However, if they enter the skin, an infection can result. Bacteria can enter through cuts, grazes, or bites.
Cellulitis can develop anywhere on the body, but in adults it most commonly affects the skin of the lower legs. In children, cellulitis often affects the face and neck, according to the American Academy of Dermatology (AAD).
Cellulitis can affect almost any part of the body. Most commonly, it occurs on the lower legs and in areas where the skin is damaged or inflamed. Anyone, at any age, can develop cellulitis. However, you are at increased risk if you smoke, have diabetes or poor circulation.
“Cellulitis literally refers to inflammation of the skin,” says Tsippora Shainhouse, MD, a board-certified dermatologist and a clinical instructor at the University of Southern California in Los Angeles.
Cellulitis is not the same as cellulite, a harmless “orange peel” effect that can appear on the upper arms and thighs.
Cellulitis can start with any break in the skin, including a minor scratch or insect bite that allows bacteria to penetrate to the deeper layers of skin. It’s rare in healthy young adults. Cellulitis is more common among elderly people and in people with weakened immune systems, chronic skin conditions that cause breaks in the skin, chronically high blood sugar levels, or obesity.
Systemic antibiotics — oral antibiotics or, in severe cases, intravenous antibiotics — are needed to treat cellulitis. Because cellulitis affects the deeper layers of skin and tissue, topical antibiotic ointments are not effective at treating cellulitis.
What Is Cellulitis?
Cellulitis is a bacterial infection of the skin and tissues beneath the skin. Unlike impetigo, which is a very superficial skin infection, cellulitis is a bacterial skin infection that also involves the skin’s deeper layers: the dermis and subcutaneous tissue.
The main bacteria responsible for cellulitis are Streptococcus and Staphylococcus (“staph”), the same bacteria that can cause impetigo and other diseases. MRSA (methicillin-resistant Staph aureus) can also cause cellulitis. Sometimes, other bacteria (for example, Hemophilus influenzae, Pneumococcus, and Clostridium species) may cause cellulitis as well.
Cellulitis is fairly common and affects people of all races and ages. Men and women appear to be equally affected. Although cellulitis can occur in people of any age, it is most common in middle-aged and elderly people. Cellulitis is not contagious.
There are different types of cellulitis, depending on where the infection occurs.
Some types include:
- periorbital cellulitis, which develops around the eyes
- facial cellulitis, which develops around the eyes, nose, and cheeks
- breast cellulitis
- perianal cellulitis, which develops around the anal orifice
Cellulitis can occur anywhere on the body, including the hands and feet. Adults tend to develop cellulitis in the lower leg, while children tend to develop it on the face or neck.
Cellulitis occurs most often on the lower leg, but other parts of the body may be affected as well. Periorbital cellulitis is cellulitis by the eye. Cellulitis may also occur on the arm, breast, abdomen, and other areas. Cellulitis symptoms may include:
Each person may experience symptoms differently. Common symptoms include:
- Redness of the skin
- Swelling of the skin
- Warm skin
- Red streaks from the original site of the cellulitis
Some cases of cellulitis are an emergency. Always talk with your healthcare provider immediately if you notice any of the following symptoms:
- A very large area of red, inflamed skin
- If the area affected is causing numbness, tingling, or other changes in a hand, arm, leg, or foot
- If the skin appears black
- If the area that is red and swollen is around your eye(s) or behind the ear(s)
- If you have diabetes or have a weakened immune system and develop cellulitis
The symptoms of cellulitis may look like other skin conditions. Always talk with your healthcare provider for a diagnosis.
The majority of cellulitis infections are caused by infection with either strep (Streptococcus) or staph (Staphylococcus) bacteria.
The most common bacteria that cause cellulitis are beta-hemolytic streptococci (groups A, B, C, G, and F). A form of rather superficial cellulitis caused by strep is called erysipelas and is characterized by spreading hot, bright red circumscribed area on the skin with a sharp, raised border. Erysipelas is more common in young children. The so-called “flesh-eating bacteria” are, in fact, also a strain of strep bacteria that can sometimes rapidly destroy deeper tissues underneath the skin.
Fasciitis is the term used to refer to inflammation of the very deep lining tissues called fascia. The streptococcal infection known as flesh-eating bacterial infection is an example of fasciitis. Cellulitis, when untreated, may rarely spread to the deeper tissues and cause serious fasciitis.
Staph (Staphylococcus aureus), including methicillin-resistant strains (MRSA), is another common type of bacteria that causes cellulitis. There is a growing incidence of community-acquired infections due to methicillin-resistant S. aureus (MRSA), a particularly dangerous type of staph infection that is resistant to many antibiotics, including methicillin, and is therefore more difficult to treat.
Cellulitis can be caused by many other types of bacteria. In children under 6 years of age, H. flu (Hemophilus influenzae) bacteria can cause cellulitis, especially on the face, arms, and upper torso. Cellulitis from a dog or cat bite or scratch may be caused by the Pasteurella multocida bacteria, which has a very short incubation period of only four to 24 hours. Aeromonas hydrophilia, Vibrio vulnificus, and other bacteria are causes of cellulitis that develops after exposure to freshwater or seawater. Pseudomonas aeruginosa is another type of bacteria that can cause cellulitis, typically after a puncture wound.
Cellulitis is not contagious because it is a soft tissue infection of the skin’s deeper layers (the dermis and subcutaneous tissue), and the skin’s top layer (the epidermis) provides a cover over the infection. In this regard, cellulitis is different from impetigo, in which there is a very superficial skin infection that can be contagious.
“Cellulitis is usually caused by a variety of bacteria, most predominantly staphylococcus (‘staph’) and streptococcal (‘strep’) species that live on the skin. These bacteria invade below the skin through abrasions and cuts, and infect the tissues beneath the skin, causing an inflammatory response,” says Amesh A. Adalja, MD, a board-certified infectious disease physician in Pittsburgh and a senior scholar at the Johns Hopkins University Center for Health Security.
While staph and strep can live harmlessly on your intact skin, any type of open sore on your body — including a burn, a surgical wound, or even a pimple — can allow the bacteria in and put you at risk of developing cellulitis, says Shainhouse.
Of course, many people sustain many minor skin wounds over the course of their lives and never develop cellulitis. But certain conditions place people at increased risk for cellulitis. Such conditions include:
- Advanced age, which is associated with a weaker immune system
- A disease that weakens the immune system, such as an autoimmune disease, diabetes, cancer, and HIV or AIDS
- Use of a medication that suppresses the immune system
- Injection of illicit drugs
- Impaired lymphatic drainage
- Obesity or being overweight
There’s also the risk of cellulitis if you have a skin condition like eczema or athlete’s foot that can cause dryness and itchiness and breaks in the skin, providing an entry point for bacteria.
Having had cellulitis once also puts you at higher risk of developing it again, according to the Mayo Clinic
Most cases of cellulitis are mild and a doctor can easily identify what is causing your skin condition. No tests are needed to diagnose mild cases of cellulitis. Sometimes doctors may order blood culture tests or tissue culture tests to identify the type of bacteria responsible for the infection. These tests may be ordered for those who suffer from severe cases of cellulitis or those who have underlying health problems.
We don’t have a medical test that can diagnose cellulitis. Doctors diagnose it by examining the infected skin and asking questions.
Be sure to tell your doctor about:
A recent injury to your skin
All medical conditions you have
All medications you take
This information can help make sure you get the treatment you need and prevent problems.
To get an accurate diagnosis, some patients need:
Medical tests: While a test cannot tell whether you have cellulitis, testing can tell what germs are causing an infection.
A referral to a dermatologist: If you are seeing a doctor other than a dermatologist, you may be sent to a dermatologist. Cellulitis can look like other skin conditions and infections.
Dermatologists have extensive training in diagnosing the many conditions that can look like cellulitis. An accurate diagnosis is essential to clear your skin condition.
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.
It’s rare, but severe cases may need surgery. For example, doctors may need to open and drain an abscess or pus that has collected in the tissue. They may also need to cut away dead tissue to allow healing.
If your cellulitis recurs, your doctor may recommend preventive antibiotics. To help prevent cellulitis and other infections, take these precautions when you have a skin wound:
- Wash your wound daily with soap and water. Do this gently as part of your normal bathing.
- Apply a protective cream or ointment. For most surface wounds, an over-the-counter ointment (Vaseline, Polysporin, others) provides adequate protection.
- Cover your wound with a bandage. Change bandages at least daily.
- Watch for signs of infection. Redness, pain and drainage all signal possible infection and the need for medical evaluation.
People with diabetes and those with poor circulation need to take extra precautions to prevent skin injury. Good skin care measures include the following:
- Inspect your feet daily. Regularly check your feet for signs of injury so you can catch infections early.
- Moisturize your skin regularly. Lubricating your skin helps prevent cracking and peeling. Do not apply moisturizer to open sores.
- Trim your fingernails and toenails carefully. Take care not to injure the surrounding skin.
- Protect your hands and feet. Wear appropriate footwear and gloves.
- Promptly treat infections on the skin’s surface (superficial), such as athlete’s foot. Superficial skin infections can easily spread from person to person. Don’t wait to start treatment.