Cellulitis is a life-threatening skin infection that often strikes the arms and legs but can appear anywhere on the body.

By Amanda MacMillan
Updated February 26, 2021

You know how important it is to thoroughly clean a cut or wound before bandaging it up in order to avoid infection. One type of infection that can develop is cellulitis, which occurs when bacteria gets past the skin’s top layer—called the epidermis—and infects the layer underneath, called the dermis.

Cellulitis causes redness, swelling, and pain in the area around the infection, and if it’s not treated early, it can lead to a systemic infection throughout the body. And while proper wound cleaning is one way to guard against the condition, cellulitis isn't always caused by an obvious injury. Here are the basics on how it happens, and how to protect yourself.

How do you get cellulitis?

Cellulitis is caused by bacteria—usually Streptococcus or Staphylococcus. These bacteria are everywhere, Arash Mostaghimi, MD, director of dermatology inpatient service at the Brigham and Women’s Hospital in Boston, tells Health; they even live on the surface of the skin. They’re usually harmless, until they make their way into the body through some opening in the skin.

Sometimes that opening is caused by an insect bite, a splinter, or some form of cut or scrape. “It’s super common for people to get a cut on their skin, say they cut themselves shaving, and then they develop cellulitis,” says Dr. Mostaghimi.

Other times, people develop cellulitis for no obvious reason. “We know there was some breach in the skin—some tiny microscopic crack, maybe—but it’s not something we can see with the naked eye or that the patient remembers happening," he adds.

Once this bacteria gets inside the body, the immune system recognizes it as a foreign object and prepares to fight it off. That’s where the symptoms of cellulitis come in: The body sends blood cells and inflammatory proteins to the affected area, which causes the skin to become red, warm to the touch, and itchy or painful.

The most common place for cellulitis to occur in adults is on the lower leg, according to the American Academy of Dermatology. But cellulitis is also common on the arms, and it can happen anywhere on the body. It can even affect the face and eyes, a condition called periorbital cellulitis.

Because the bacteria that causes cellulitis is so common—and so are cuts, scrapes, and breaks in the skin—it’s not clear to doctors why some people develop cellulitis while others never do. But there are some things that put certain people more at risk for the condition than others.

How can you protect yourself?

People who have a chronic illness or are taking drugs that suppress the immune system (for an autoimmune disease or after an organ transplant, for example) are at increased risk for developing cellulitis, as well as more serious complications from it. “If you have a compromised immune system, your body isn’t going to be able to fight the bacteria as effectively,” says Dr. Mostaghimi.

Conditions that cause circulation issues and reduced blood flow throughout the body also raise the risk of cellulitis. That includes people with diabetes and lymphadema, a condition that causes swelling in the arms or legs. Being overweight has also been linked to an increased likelihood of developing cellulitis.

Practicing proper wound cleaning—washing cuts and wounds with soap and water as soon as possible, and applying an antibacterial ointment like Neosporin—is one big way people can protect themselves from cellulitis, says Dr. Mostaghimi. This is important for everyone, he adds, but is especially important if you fall into any of the categories above.

Keeping skin moisturized can also be helpful, since it can help prevent tiny cracks in the epidermis. And because fingernails and toenails can harbor bacteria—which can be transferred when scratching insect bites and other wounds—keep them clean and trimmed, as well.