Impetigo is caused by common bacteria that may be naturally present on the skin. It usually affects children and can spread rapidly wherever groups of children are in close contact, such as in schools and childcare settings.

Risk factors for developing impetigo include:

• Direct skin-to-skin contact with a person who has the disease or with contaminated objects (e.g., towels, bedding, clothing). Blisters typically appear within four to 10 days after coming into contact with fluids from the lesions of an infected person.
  
  
• Minor cuts, wounds, burns and/or other trauma that causes a break in the skin.
  
  
• Weakened or underdeveloped immune system. People suffering from diseases that weaken the immune system, such as diabetes, may be more prone to becoming infected. Children have underdeveloped immune systems which put them at risk for infection. In addition, prolonged use of antibiotics may weaken the immune system.  
  
  
• Warm, humid weather. Impetigo occurs more often during the summer and early fall. High temperature causes a disruption in the skin’s natural flora (harmless bacteria) and may predispose it to infection from bacteria.
  
  
• Chronic skin diseases (e.g., eczema).
  
  
• Crowded conditions, especially places where there is poor hygiene.

Impetigo occurs when the toxins produced by either the Staphylococcus aureus (staph) or Streptococcus pyogenes (strep) bacteria, or a combination of the two, enter the skin. The staph and strep bacteria are often present in the nose or on the skin and are generally harmless in those locations. When they enter the skin, however, the bacteria attack a protein that helps bind skin cells together. After this protein is damaged, germs can spread quickly and infection begins.