Cellulitis 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. 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.
Cellulitis appear on areas of trauma, where the skin has broken or open, such as the skin near ulcers or surgical wounds. Many times, however, cellulitis occurs where there has been no break in the skin at all. Patients who have diabetes or impairment of the immune system (for example, from HIV/AIDS or from drugs that suppress the immune system) are particularly prone to developing cellulitis.
Staphylococcus aureus is the most common bacteria that causes cellulitis. Streptococcus is the next most common bacteria that causes cellulitis. In children under age 6, H. flu (Hemophilus influenzae) bacteria can cause cellulitis, especially on the face, arms, and upper torso.
Cellulitis from a dog or cat bite or scratch may be caused by the Pasturella multocida bacteria, which has a very short incubation period of only four to 24 hours.
Cellulitis after an injury from a saltwater fish or shellfish (like a fish bite, a puncture from a fish spine, or a crab pinch) can be due to the Erysipelothrix rhusiopathiae bacteria. These same bacteria can also cause cellulitis after a skin injury on a farm, especially if it happened while working with pigs or poultry.