Impetigo is a highly contagious skin condition, and is the most common skin infection that affects children. It is caused by either the Staphylococcus aureus (staph) or Streptococcus pyogenes (strep) bacteria, and sometimes a combination of the two. Adults also get impetigo, frequently from contact with infected children.

The skin normally has many harmless types of bacteria living on it, known collectively as the skin flora. These bacteria live in the skin’s hair follicles and in sebaceous glands that moisten the skin. They also protect the body from more harmful bacteria. The skin itself also provides a major barrier to keep both the bacteria in the skin flora and other harmful organisms from entering the body. However, when there is a break in the skin (e.g., from a cut, bruise or other form of trauma), bacteria can enter the body and cause inflammation and infection. Other factors may also affect the skin flora and make it susceptible to infection, including high temperatures or humidity, pre-existing skin infections and prolonged use of antibiotics, which can lower a person’s ability to fight infection.   

When impetigo occurs, bacteria enter the skin’s outer layer (epidermis) and form skin lesions that may ooze and form crusts. These lesions are extremely contagious. Touching, rubbing or scratching them often leads to their spread to other parts of the body.

Typically, impetigo is acquired by direct skin-to-skin contact with an infected person. People can also become infected through contact with infected objects (e.g., utensils, clothes, toys, doorknobs). Children pass it during contact at school or while playing. Impetigo is more common in warmer weather and tropical climates. It occurs more readily in crowded conditions and in areas where there is inadequate hygiene.

Most cases of impetigo occur among children between 2 and 6 years old, although a less common form occurs among infants.

Impetigo is seldom serious, especially if treated early. The lesions clear up within a few weeks, although scarring can sometimes occur. In a few rare cases, impetigo can spread to other parts of the body and lead to complications. These may include:

• Cellulitis. An infection affecting the tissues underneath the skin that spreads to the lymph nodes and bloodstream.
  
  
• Post-streptococcal glomerulonephritis. A rare complication of impetigo resulting in inflammation of the kidneys, which may lead to kidney failure.