What is impetigo?

Impetigo, commonly known as school sores, is a bacterial skin infection. It is characterised by itchy, red sores and/or blisters that may pop to produce a yellow-to-brown crust. Although impetigo can occur in anyone, it usually affects children between 2-6 years of age. It can develop anywhere on the body, but is most common around the mouth and nose. 

Causes

Impetigo is caused by infection of the skin due to Streptococcus pyogenes and/or Staphylococcus aureus bacteria. Sometimes, Streptococcus pyogenes bacteria is also known as Group A Streptococcus bacteria (GAS) or group A beta-haemolytic streptococcus (GABHS). In recent times, a strain of the bacteria called methicillin-resistant Staphylococcus aureus (MRSA) has become a common cause of impetigo. The term 'methicillin-resistant' means that these bacteria are no longer destroyed by penicillin-based antibiotics, which are a common therapy for bacterial skin infections. These bacteria can live on the skin and in the nose without causing any harm. Impetigo generally occurs when the bacteria get past the skin's natural barrier, usually through a break in the skin. Common causes for skin damage are insect bites, cuts and scratches, and other skin conditions, such as eczemahead lice or scabies. However, impetigo can also affect healthy skin that has no obvious signs of damage. 

Once the bacteria enter through skin breaks, it causes localised inflammation in the top layers of the skin. This leads to the characteristic symptoms of red sores, fluid-filled blisters, and crusting on the skin. 

Impetigo is easily spread through direct contact with an infected person. Sores and fluid from the nose and throat contain large numbers of Streptococcus pyogenes and/or Staphylococcus aureus bacteria. These can be spread to other areas of the body or another person by scratching and touching the sores.

A cross-section of healthy skin compared to a cross-section showing the characteristic crust, sores and inflammation of impetigo.Healthy skin compared to skin infected with impetigo. 

Risk factors

Risk factors that may increase the likelihood of developing impetigo include:

  • Age - most cases of impetigo occur in children aged between 2-6 years, (typically when starting pre-school or school);
  • Close contact with another person who has the condition;
  • Poor hygiene and lack of hand-washing habits;
  • Crowded living conditions;
  • Living in a hot, humid climate;
  • Another skin condition, such as eczema, head lice or scabies;
  • An existing skin injury, such as an insect bite, cut or scratch, and;
  • Certain other medical conditions that weaken the immune system, such as chickenpox or diabetes.

Diabetes

A metabolic disorder that is caused by problems with insulin secretion and regulation and which is characterised by high blood sugar levels. Also known as diabetes mellitus.

Immune system

The organs and cells involved in protecting the body against infection.

Types

There are two types of impetigo:

Non-bullous impetigo

Also known as vesiculopustular impetigo, this type of infection may be caused by either Streptococcus pyogenes or Staphylococcus aureus bacteria. Non-bullous impetigo is characterised by red sores that quickly form ulcers and then produce a yellow-to-brown crust a few days later. A red mark may also appear after crusting, which can take a few days or weeks to clear.

Bullous impetigo

Bullous impetigo is caused by Staphylococcus aureus bacteria. It is less common, but more contagious than the non-bullous type. The name originates from the medical word, 'bulla', which means a large, fluid-filled blister. These blisters usually occur under the nappy line in babies, or on the torso, arms or legs. After several days, the blisters usually burst and then form a yellow crust. There may be accompanying symptoms of fever, swollen lymph nodes and/or unwellness.

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Ulcers

An open sore in the skin or mucous membranes such as those of the stomach lining, intestine or mouth.

Signs and symptoms

Symptoms of impetigo usually develop about 4-10 days after coming into contact with an infected person. The condition often starts with a rash of just a few spots or blisters that can spread to other areas. It may also lead to infection in other people before the condition has been identified.

In general, the signs and symptoms of impetigo include:

  • Red, itchy patches of skin, often more than one centimetre across;
  • Blisters, most commonly around the mouth and nose;
  • Burst blisters that ooze a sticky, yellow fluid; and
  • Crusted sores.

Rarely, there can be accompanying symptoms of fever, swollen lymph nodes and feeling of unwellness.  

Young boy with impetigo sores around the mouth and nose.Impetigo sores around the mouth and nose. 

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Methods for diagnosis

Your doctor will most likely diagnose impetigo by looking closely at your skin and asking questions about symptoms.

If symptoms don't respond to treatment or keep coming back, your doctor may take a swab of the blisters or sores to see which bacteria are present. This can also help to determine the most appropriate antibiotics to treat the bacteria. 

Doctor swabbing broken skin.A swab of the infected skin to test for bacterial presence. 

Types of treatment

Impetigo is generally treated using good cleaning habits and antibiotics. Keeping children with impetigo home, is recommended to help prevent the spread of infection. It is generally advised, that they should be kept away from other children until the skin is completely healed. 

The treatment may vary with the severity of the symptoms. The doctor is likely to recommend the following: 

Self-care

To help prevent the spread of infection, it is important to practice regular hand-washing. Also, treating affected areas of skin with an antibacterial solution, such as chlorhexidine or povidone-iodine, can further reduce spread of the infection. Other skincare measures may include covering sores with a waterproof dressing and avoiding scratching. Soaking off any crusts with warm water can help the skin to better absorb antibacterial medications.

Medications

In mild cases of impetigo, your doctor may prescribe an antibiotic ointment. These are applied directly to the skin, usually three times per day for several days.

For more severe or widespread infection, an oral antibiotic may be prescribed. Some examples of oral antibiotics given for impetigo include flucloxacillin, dicloxacillin and cephalexin. These antibiotics will not be effective against methicillin-resistant Staphylococcus aureus (MRSA), which requires more tailored antibiotics. 

If impetigo keeps coming back, your doctor may prescribe oral antibiotics on a long-term basis, or to use at the earliest sign of infection. For all types of antibiotic treatment, taking the full course prescribed by your doctor is important to ensure that the infection is completely cleared. Sometimes the nostrils may be treated with an antibiotic ointment, if your doctor suspects the nose to be the source of recurrent infections.

Potential complications

Most cases of impetigo are successfully treated with antibiotics. While impetigo can sometimes look unsightly, long-term scarring and complications are not common. Rarely, a deeper form of impetigo can develop, usually on the legs or other areas. This condition, known as ecthyma, is characterised by ulcers beneath the typical crusted sores. This condition generally requires oral antibiotics, which is continued for a longer period of time. 

Impetigo can also be serious in newborn babies, as their immune systems may not be able to recognise and fight a bacterial infection effectively. If symptoms appear on your newborn baby, seek prompt medical attention.

Impetigo can occasionally recur, especially if not adequately treated. In rare cases, if left untreated, the infection can spread to other areas and result in: 

In very rare cases, impetigo can lead to scarring. However, this mainly occurs due to excessive scratching of the affected skin.

Immune systems

The organs and cells involved in protecting the body against infection.

Sepsis

An illness caused by inflammation throughout the body in response to an infection. It can be life-threatening if it leads to septic shock, a dramatic loss of blood pressure.

Ulcers

An open sore in the skin or mucous membranes such as those of the stomach lining, intestine or mouth.

Glomerulonephritis

A group of conditions in which the part of the kidneys that helps filter the blood is damaged.

Prognosis

The outlook for impetigo is good when it's treated early with good skin-care and antibiotics as required. Although the condition may be itchy and unsightly, it generally is not painful and is unlikely to cause long-term scarring. The cure rate is high, but impetigo may come back, especially in young children.

Prevention

Impetigo may be prevented by avoiding contact with people who have the condition. If contact can't be completely avoided, the likelihood of developing impetigo may be reduced by keeping the skin clean and limiting the sharing of food, drinks, bathwater, towels or other personal items. At present, there are no vaccinations to prevent this condition.