There are two major types of impetigo:

• Nonbullous impetigo. This form of impetigo – also called impetigo contagiosa – is the most common form. It is usually caused by either the Staphylococcus aureus (staph) or Streptococcus pyogenes (strep) bacteria, or a mix of the two. Infection typically occurs at sites of trauma to the skin, such as a chickenpox sore, insect bite, cut or other laceration that results in a break in the skin. Specifically, these bacteria attack a protein that helps bind skin cells together. When this protein is damaged, the bacteria invade and establish infection in the skin. This form of impetigo usually occurs among children between 2 and 6 years of age, often during warmer months.
  
  Ecthyma is a rare form of nonbullous impetigo that penetrates deep into the skin’s second layer (dermis). The streptococcal bacterium is the most common infectious organism associated with ecthyma. The infection may begin at the site of an injury, such as a scratch or insect bite, and often affects the legs.
  
  
• Bullous impetigo. This form of impetigo is caused by the staph bacteria. In contrast to the nonbullous form, bullous impetigo results from invasion by only staph bacteria into either intact or broken skin. Infection usually occurs after the bacteria colonize the upper respiratory tract, usually the nostrils. Bullous impetigo is much less common than nonbullous impetigo and may occur in infants.