What Is It?
Cellulitis is a serious bacterial infection of the skin. In cellulitis, bacteria penetrate the skin's protective outer layer, typically at the site of an injury, such as a cut, puncture, sore, burn or bite. Cellulitis also can occur at the site of surgery, or where the skin was punctured for a small plastic tube (intravenous catheter) used to administer medications. Once inside the skin, the invading bacteria multiply and make chemicals that cause inflammation in the skin.
Cellulitis usually occurs on the legs and feet. However, it can develop on any part of the body, including the trunk, arms and face. It often develops near an area where there already is swelling, poor blood flow, or another skin condition such as a fungus infection between the toes (athlete's foot).
Many different types of bacteria can cause cellulitis. However, most cases are caused by Streptococcus pyogenes (strep) or Staphylococcus aureus (staph). Other types of bacteria can cause infection after certain types of skin injuries, such as animal bites, puncture wounds through wet shoes, and wounds exposed to freshwater lakes, aquariums, or swimming pools.
Cellulitis can take several specific forms, including:
Periorbital cellulitis, a skin infection around the eye sockets (orbits) - Often, this is caused by Haemophilus influenza, a type of bacterial infection that is common in children. Because infection around the eye can spread to the brain, periorbital cellulitis requires prompt medical attention.
Erysipelas, a form of skin infection that causes raised, firm, bright red patches of skin - Usually, it is caused by Streptococcus bacteria. Erysipelas occurs most often on an arm or leg that has been damaged by previous surgery or is chronically swollen due to poor lymph flow (lymphedema). Erysipelas also can develop on the face, typically across the bridge of the nose and upper cheeks.
Necrotizing fasciitis, also known as "flesh-eating strep" - This is an infection of the tissues below the skin, rather than the skin itself. Often, the skin in the area is discolored and extremely painful. Fasciitis is a life-threatening infection that requires prompt medical attention.