Causes of impetigo 

Impetigo occurs when the skin becomes infected with bacteria, usually either Staphylococcus aureus or Streptococcus pyogenes.

These bacteria can infect the skin in two ways:

  • through a break in otherwise healthy skin, such as a cut, insect bite or other injury – this is known as primary impetigo
  • through skin damaged by another underlying skin condition, such as head lice, scabies or eczema – this is known as secondary impetigo

The bacteria can be spread easily through close contact with someone who has the infection, such as through direct physical contact, or by sharing towels or flannels.

As the condition does not cause any symptoms until four to 10 days after initial exposure to the bacteria, it is often easily spread to others unintentionally.

Impetigo stops being infectious after 48 hours of treatment starting or after the sores have stopped blistering or crusting.

Increased risk

In addition to the situations mentioned above, there are a number of other factors that can increase your chances of developing impetigo. These include:

  • being a child – impetigo is thought to be more common in children because their immune system has not yet fully developed and because they tend to spend time in places where the infection can easily be spread, such as schools and nurseries
  • having diabetes
  • being a carrier of Staphylococcus aureus bacteria – these bacteria can live in the noses of some people without causing problems, but they can sometimes cause impetigo if they get into damaged skin nearby
  • warm and humid weather – impetigo tends to be more common during the summer months in the UK, possibly because the warm and moist weather is a better environment for the bacteria to grow and/or because the skin is more likely to be exposed to insect bites and cuts at this time of year
  • having a weakened immune system, either due to a condition such as HIV or a treatment such as chemotherapy

Page last reviewed: 17/07/2014

Next review due: 17/07/2016