What Are the Key Factors That Lead to Cellulitis?

The most common causes of cellulitis are streptococcus and staphylococcus, though other bacterial strains, like methicillin-resistant Staph aureus (MRSA), can cause it as well. Many of these bacteria live on our skin all the time without causing a problem, but if the bacteria gets under the top surface of the skin, it can lead to a deep infection.

Anything that damages the integrity of the skin can allow bacteria to enter, including injuries and trauma. Though other factors will also affect the amount of risk, any cut, scratch, scrape, or puncture can lead to cellulitis, whether they occur accidentally or as the result of a surgical procedure. This includes burns and even fractures and sprains with a break in the skin.

Cellulitis can result from any bite, whether from an insect, animal, or human. It is a known complication of animal bites, and human bites get infected between ten and 30 percent of the time, often leading to cellulitis.

Insect bites are one of the most common causes of cellulitis around the eyes. There is some added risk with itchy insect bites, as scratching can further damage skin integrity, making it more likely for bacteria to enter.

Ulcers caused by diseases like diabetes and vascular disease increase the risk of developing cellulitis. About 25 percent of people with diabetes develop foot ulcers. Because diabetes can also cause nerve damage, people may not even realize the ulcers are there, leading to cellulitis and other infections.

Vascular disease can lead to open sores, usually in the legs, which are slow to heal, making them a significant risk for infection.

Any medication that suppresses the immune system, including corticosteroids and chemotherapy, increases the risk of infection. People take immunosuppressive drugs for many reasons, including to treat cancer and autoimmune diseases and after organ transplantation to prevent rejection. Their bodies cannot fight off infection effectively, meaning that even minor cuts and scrapes might lead to a cellulitis infection without proper treatment.

Surgical procedures account for a quarter of all hospital stays, and between two and four percent of patients undergoing inpatient surgeries get some kind of surgical site infection, one of which is cellulitis. Some common inpatient procedures that may lead to infection include cesarean section, hip and knee replacement, and hip fracture repair.

Peripheral vascular disease or peripheral artery disease is a systemic disorder that happens when the peripheral blood vessels narrow due to a buildup of plaque. Blood flow to the arms and legs is restricted, which can lead to tissue damage and pain.

Breaks in the skin and the lack of blood flow make people with peripheral vascular disease prone to infections, including cellulitis.

Cracks or peeling skin between the toes is commonly caused by athlete's foot, a fungal infection that can also cause redness, swelling, and itchiness. This infection generally does not go away on its own. A bacterial infection like cellulitis from athlete's foot is rare, but it can happen in severe cases.

Doctors usually diagnose cellulitis by taking a patient history and doing a physical examination. Generally, blood cultures and swabs of the infected area are not necessary; however, in cases of severe infection or for immunosuppressed patients, cultures can identify the specific bacteria causing the infection so they can receive more targeted treatment.

Erysipelas and cellulitis are both skin infections that develop from bacteria entering the skin. They even have similar symptoms, with both causing swelling, pain, and redness. The main difference between the two is that erysipelas usually only affects the top layers of the skin, while cellulitis goes deeper into the tendons and muscles.

On the surface of the skin, erysipelas appears shiny and well-defined, while cellulitis is less clearly defined and may look slightly purplish.