John L. Brodhead Jr., USC associate professor of internal medicine, describes the skin problem that is especially common in children or immunocompromised adults.

What is cellulitis?

Cellulitis is an infection of the skin that may affect any part of the body, but usually appears on the lower legs or face.

What causes it?

Lots of different bacteria can cause cellulitis. Some might come from dog or cat bites, others from farm animals, still others from simple scratches and scrapes. Cellulitis also can come from fungal infections, such as athlete's foot.

What are its symptoms?

An area of tenderness, swelling and redness appears under the skin-oftentimes where skin has been broken with a cut or scratch. Sometimes fever, sweating and swollen glands may accompany the spreading area of redness. Sometimes people with diabetes or immune problems get cellulitis without a break in the skin.

How is it treated?

Doctors look at the affected area and sometimes ask for a blood test to check for infection. If cellulitis is the answer, doctors give patients antibiotics, which help the body get rid of bacteria. In the case of a fungal infection, doctors can give patients anti-fungal medications.

Are there any herbal medicines that work?

There are no good scientific studies showing beneficial herbal treatments, and no evidence any other methods may help. In fact, if an infection is the cause, not treating it with antibiotics could allow the infection to spread. If bacteria enter the bloodstream, they can cause a more serious and potentially life-threatening condition called sepsis. The infections can also result in large boils, filled with pus, which a doctor must remove.

Can it be prevented?

Anything that protects skin from cuts and scratches, like protective equipment during exercise, helps. After a scrape or wound, a good tip is to wash the area with soap and water, dry it lightly, treat it with an antibiotic ointment and cover it with an adhesive strip or bandage.