Cellulitis (sel-u-LI-tis) is a common, potentially serious bacterial skin infection. Cellulitis appears as a swollen, red area of skin that feels hot and tender, and it may spread rapidly.

Skin on lower legs is most commonly affected, though cellulitis can occur anywhere on your body or face. Infections on the face are more common in children and older adults. Cellulitis may affect only your skin's surface — or, cellulitis may also affect tissues underlying your skin and can spread to your lymph nodes and bloodstream.

Left untreated, the spreading infection may rapidly turn life-threatening. That's why it's important to seek immediate medical attention if cellulitis symptoms occur.

Click to Enlarge

Cellulitis

Cellulitis symptoms may mean that your skin is:

• Red
• Swollen
• Tender
• Warm

The changes in your skin may be accompanied by a fever. Over time, the area of redness tends to expand. Small red spots may appear on top of the reddened skin, and less commonly, small blisters may form and burst.

Cellulitis occurs when one or more types of bacteria enter through a crack or break in your skin. The two most common types of bacteria that are causes of cellulitis are streptococcus and staphylococcus. The incidence of a more serious staphylococcus infection called methicillin-resistant Staphylococcus aureus (MRSA) is increasing.

Although cellulitis can occur anywhere on your body, the most common location is the legs, especially near your shins and ankles. Disrupted areas of skin, such as where you've had recent surgery, cuts, puncture wounds, an ulcer, athlete's foot or dermatitis, serve as the most likely areas for bacteria to enter.

Certain types of insect or spider bites also can transmit the bacteria that start the infection. Areas of dry, flaky skin also can be an entry point for bacteria, as can swollen skin.

Several factors can place you at greater risk of developing cellulitis:

• Age. As you age, your circulatory system becomes less effective at delivering blood — with its infection-fighting white blood cells — to some areas of your body. As a result, skin abrasions may lead to infections where your circulation is poor.
• Weakened immune system. Illnesses that result in a weakening of your immune system leave you more susceptible to infections such as cellulitis. Examples of these illnesses include chronic lymphocytic leukemia and HIV infection. Taking immune-suppressing drugs, such as prednisone or cyclosporine, also can leave you more vulnerable to infections. Immune-suppressing drugs are used to treat a variety of illnesses and to help prevent rejection in people who receive organ transplants.
• Diabetes. Having diabetes not only increases your blood sugar level but also impairs your immune system and increases your risk of infection. Your skin is one of the many areas of your body that becomes more susceptible to infection. Diabetes may result in decreased circulation of blood to your lower extremities, potentially leading to chronic ulcers of your feet. These ulcers can serve as portals of entry for bacterial infections.
• Chickenpox and shingles. These common viral diseases typically cause broken blisters on the skin that can serve as potential entry points for bacterial invasion and infection.
• Chronic swelling of your arms or legs (lymphedema). Swollen tissue may crack, leaving your skin vulnerable to bacterial infection.
• Chronic fungal infection of your feet or toes. Recurrent fungal infection of your feet or toes can cause cracks in your skin, increasing your risk of bacterial infection.
• Intravenous drug use. People who inject illicit drugs have a higher risk of developing cellulitis.

If you have a rash that's red, swollen, tender and warm — and it's expanding — try to see your doctor the same day. If a fever or pain accompanies the rash, or the rash is changing rapidly, seek emergency care. It's important to identify and treat cellulitis early because the condition can cause a serious infection by spreading rapidly throughout your body.

The appearance of your skin will help your doctor make a diagnosis. Your doctor may also suggest blood tests, a wound culture or other tests to help rule out a blood clot deep in the veins of your legs. Cellulitis in the lower leg is characterized by signs and symptoms that may be similar to those of a clot occurring deep in the veins, such as warmth, pain and swelling.

This reddened skin or rash may signal a deeper, more serious infection of the inner layers of skin. Once below your skin, the bacteria can spread rapidly, entering your lymph nodes and your bloodstream and spreading throughout your body.

In rare cases, the infection can spread to the deep layer of tissue called the fascial lining. Flesh-eating strep, also called necrotizing fasciitis, is an example of a deep-layer infection. It represents an extreme emergency.

Cellulitis treatment may involve a prescription oral antibiotic. You'll likely recheck with your doctor one to two days after starting an antibiotic to ensure that the infection is responding to treatment. You'll need to take the antibiotic for 10 to 14 days. In most cases, signs and symptoms of cellulitis disappear after a few days. If they don't clear up, if they're extensive or if you have a high fever, you may need to be hospitalized and receive antibiotics through your veins (intravenously).

Usually, doctors prescribe a drug that's effective against both streptococci and staphylococci. An example is cephalexin (Keflex). Your doctor will choose an antibiotic based on your circumstances.

No matter what type of antibiotic your doctor prescribes, it's important that you take the medication as directed and that you finish the entire course of medication, even if you start feeling better.

To help prevent cellulitis and other infections, follow these measures anytime you have a skin wound:

• Wash your wound daily with soap and water. Do this gently as part of your normal bathing.
• Apply an antibiotic cream or ointment. For most surface wounds, a single- or double-antibiotic ointment provides adequate protection.
• Cover your wound with a bandage. This helps keep the wound clean and bacteria out. If you have draining blisters, keep them covered until a scab forms.
• Change bandages often. Change them at least daily or whenever the bandage becomes wet or dirty.
• 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 wounds and treat any cuts or cracks in the skin promptly. Good skin-care measures include the following:

• Moisturize your skin regularly. Lubricating your skin helps prevent cracking and peeling.
• 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 any superficial skin infections, such as athlete's foot. Infections on the surface of the skin (superficial) can easily spread from person to person. Don't wait to start treatment.