What Is Cellulitis? - Definition, Causes, Symptoms & Treatment

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  • 0:00 Definition
  • 0:33 Causes
  • 1:22 Symptoms
  • 1:49 Treatment
  • 2:16 Lesson Summary
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Lesson Transcript
Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Cellulitis is a bacterial skin infection that can be serious. Complete this lesson to learn how it develops, what causes it, what the symptoms are, and how to treat it. Then, test your understanding with a brief quiz.


Cellulitis (not to be confused with cellulite, which is fat found beneath the skin) is a bacterial skin infection that can be serious. It affects both the skin's surface and the tissues underneath, and it causes the affected area to turn red and become swollen, usually causing pain. This type of condition is relatively common and is not contagious. Once a person becomes infected with cellulitis, it can spread quickly to the rest of the body; it most commonly affects the lower extremities. If left untreated, it may also spread to the lymph nodes and circulatory system.


As stated earlier, cellulitis is caused by a bacterial infection of the skin. Usually, the bacterial strains streptococcus and staphylococcus are responsible for the infection. Any opening in the body, like a cut or wound, can provide a gateway for infection. Cellulitis can occur after surgery, as a result of long-term skin conditions, piercings or other foreign objects stuck in the skin, or as a result of bone infections. Insect bites and extreme dry skin may also provide entry points for bacteria, especially because these bacteria may linger on the skin. Though cellulitis can happen to anyone, there are identified risk factors increasing the probability of developing an infection. These include having a history of cellulitis, obesity, intravenous drug use, skin conditions, diabetes, and other diseases that weaken the immune system.


If cellulitis forms, there are several common symptoms. They include:

  • Swelling and redness
  • Skin sensitivity - it's sore and tender to the touch
  • Pain or warmth
  • Blisters
  • Red spots
  • Fever
  • Dimpling of the affected area
  • Appearance or leaking of pus

Immediate medical care is needed if the following serious symptoms develop:

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