What Is Cellulitis?

Cellulitis is a common bacterial infection of the deeper layers of the skin, specifically the dermis and subcutaneous tissue. In addition to skin redness, swelling, and warmth, which often spread quickly, a person may also experience fever and/or chills, especially if the infection is severe. Any break in the skin can leave you vulnerable to this infection. And while often effectively treated with antibiotics, certain cases can be life-threatening.

Cellulitis Symptoms

Cellulitis causes your skin to be red, swollen, tender, and warm to the touch. In addition, sometimes the texture of the infected skin will be described as "cobblestone" in appearance.

Red streaks radiating from the area and swollen lymph nodes are also common features of cellulitis. Fever, chills, and/or fatigue may be present as well, especially if the infection is severe.

Causes

Cellulitis is almost always caused by a bacterial infection. Bacteria are able to enter the body through breaks in the skin, such as from a cut, scrape, ulcer, spider bite, tattoo, or surgical wound. Skin conditions, like eczema, athlete's foot, or very dry skin, can also lead to skin cracks that provide an opening for bacteria.

In adults and children, cellulitis is most often caused by Streptococcus and Staphylococcus aureus bacteria. Another type of bacteria, Haemophilus influenzae type B, can cause cellulitis in children younger than 3 years of age, but this has become less common since vaccinations against this bacteria have become routine.

Animal bites, such as a from a dog or cat, may lead to an infection with Pasteurella multocida. Dog bites may rarely cause an infection with Capnocytophaga, which can be fatal in those with alcoholism, without spleens, or who have underlying liver disease.

Exposing a wound to warm salt water may lead to cellulitis from Vibrio vulnificus. While the cellulitis is generally mild, in high-risk individuals—those with liver or alcohol problems, or a chronic illness like diabetes—the infection may spread rapidly and become life-threatening.

This can be caused by any number of things, including:

• Prior cellulitis infection
• Surgical removal of lymph nodes, which may lead to lymphedema
• Removal of veins for vein grafts elsewhere in the body
• Prior or current radiation therapy to the area in question

Other factors that increase a person's chance for developing cellulitis include:

• Being overweight or obese
• Increasing age
• Having diabetes, HIV, or AIDs
• Taking a medication that suppresses your immune system (e.g., a corticosteroid or chemotherapy)
• Leg swelling from venous insufficiency, congestive heart failure, or liver/kidney disease

Diagnosis

Cellulitis is usually diagnosed based on its appearance. Sometimes doctors will check a person’s blood count to see if the white blood cells are elevated (meaning that the immune system is fighting an infection). That said, an elevated white blood cell count may not occur in the early stages of an infection.

In people who are very ill, blood cultures may be performed to see if the bacteria has spread into the bloodstream. Unfortunately, cultures are only positive in less than 10 percent of cases, making a definitive diagnosis difficult.

Less commonly, a doctor may opt to perform an aspiration, which involves the injection of sterile fluid into the infected tissue, after which fluids are drawn out in the hopes of capturing some of the bacteria. This is usually done only in extreme cases since aspirations may return inconclusive results.

Also less commonly, a skin biopsy culture—where a small sample of the affected skin is removed and placed in a Petri dish to see if bacteria grow—may be performed if the diagnosis is uncertain and/or to rule out diagnoses that can mimic cellulitis, like or a drug reaction or vasculitis.

Finally, imaging tests, such as an ultrasound or magnetic resonance imaging (MRI), may be used to distinguish cellulitis from another diagnosis, like a deep venous thrombosis (DVT) or osteomyelitis (a bone infection).

Treatment

Cellulitis is treated with antibiotics, which are medications that target bacteria. Most cellulitis infections require a 10-day course of an oral antibiotic, although the precise duration will ultimately depend on the severity of the infection.

Most people will note symptom improvement within 24 to 48 hours of starting their antibiotic.

Besides taking an antibiotic as prescribed by your doctor, if the infection is on an arm or leg, elevating the extremity can speed healing. Rest is also important for the healing process. Additionally, your doctor may recommend a special dressing to keep the infected skin covered.

For more severe cases of cellulitis, hospitalization and intravenous antibiotics may be required. Examples of such cases include:

• Cellulitis of the face
• Persons who are seriously ill
• People who are immune compromised

In addition, infections that don't improve or get worse with oral antibiotics require immediate medical attention.

Serious complications may arise from untreated cellulitis including sepsis (when the bacteria enters your bloodstream), necrotizing fasciitis (when the infection reaches deeper tissues), and abscess formation.

Prevention

The best prevention of cellulitis is to take care of any break in the skin, which includes:

• Washing the wound daily with soap and water
• Applying a topical antibiotic to the wound
• Keeping the wound covered with a bandage
• Changing the bandage daily (or more often if it gets dirty or wet)

It's also important to address with your doctor any underlying health condition that is increasing your risk for developing cellulitis, such as poorly controlled diabetes, obesity, or extremely dry skin.

A Word From Verywell

Never hesitate to see a doctor if a wound you are nursing suddenly gets redder, becomes painful, or starts draining. This is especially true if you have diabetes, are experiencing poor circulation, or are taking immune-suppressing drugs.

Waiting is rarely a good idea. A persistent rash or skin that is deep red and inflamed may signal a more serious infection of the dermis (the inner layer of skin). As with all skin disorders, earlier detection allows for more effective treatment.