Cellulitis occurs when one or more types of bacteria enter the body. The most common types of bacteria that cause cellulitis include streptococcus and staphylococcus.

There are many injuries and conditions that can cause bacteria to enter the body and lead to cellulitis. They include:

• Cuts or scrapes
  
  
• Puncture wounds (including body piercings)
  
  
• Burns
  
  
• Ischemic ulcers (non-healing sores on the hands and feet)
  
  
• Athlete’s foot (contagious infection of the feet caused by fungi)
  
  
• Skin disorders, such as dermatitis
  
  

  

• Surgery
  
  
• Certain types of insect and spider bites
  
  
• Animal or human bites
  
  
• Areas of dry, flaky skin
  
  
• Chickenpox and shingles (common viral diseases that cause blisters on the skin)

There is increased risk for cellulitis if there are breaks in the skin barrier when handling fish, shellfish, poultry, eggs or meat. The bacteria that reside normally on fish, poultry or livestock are not common to humans and can infect the skin through an open wound.

Other conditions and diseases that increase the risk of developing cellulitis include:

• Recent heart, lung, dental or other procedures
  
  
• Use of corticosteroids
  
  
• Alcoholism
  
  
• Diabetes
  
  
• Intravenous drug abuse
  
  
• Peripheral vascular disease (disease of the blood vessels outside the heart and brain)
  
  
• Poor circulation or heart failure
  
  
• Lymphedema (chronic swelling of the arms and legs)

Age also affects a person’s risk for developing cellulitis. As people age, their circulatory system becomes less efficient at delivering blood. Since blood contains infection-fighting white blood cells, poor circulation may lead to cellulitis, as well as other infections.

People with a compromised immune system are also more likely to develop the condition. This group includes AIDS patients, cancer patients and those taking certain immunosuppressants.