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Abscess - Causes of an abscess

NHS Choices Medical Reference

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Most abscesses are caused by a bacterial infection.

Bacteria

When bacteria enter your body, your immune system tries to fight the infection by sending white blood cells to the affected area. As the white blood cells attack the bacteria, it causes inflammation (swelling) and the death of nearby tissue, leading to the formation  of a cavity.

The cavity fills with pus to form the abscess. The pus contains a mixture of dead tissue, white blood cells and bacteria. The abscess may get larger and more painful as the infection continues and more pus is produced.

Staphylococcus aureus and streptococci are the most common types of bacteria that cause skin abscesses on the following areas of the body:

  • head and neck
  • limbs
  • underarms
  • torso

Read more information about Staphylococcal infections.

PVL Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a type of bacterium found on the surface of healthy skin, particularly in the nose and moist, damp areas such as armpits and groins. It can cause skin infections, such as skin abscesses and boils, and prefers to live in moist areas of the body such as the armpits and groin. 

Some S. aureus bacteria can produce a poisonous substance called Panton-Valentine leukocidin (PVL), which kills the white cells, causing the body to make more white cells to continue to fight the infection.

PVL-positive strains of bacteria are therefore more likely to cause skin infections and abscesses.

Both types of S. aureus can also cause more serious conditions such as:

  • septicaemia - blood poisoning caused by bacteria multiplying in the blood
  • pneumonia - swelling (inflammation) of the lungs caused by an infection

Skin abscesses

Bacteria can cause a skin abscess when they get under the surface of your skin. An abscess may occur if you have a minor skin wound, such as a small cut or graze, or if a sebaceous gland (oil gland) or a sweat gland in your skin becomes blocked.

Boils develop as the result of bacteria entering the root of a hair on your skin.

In most cases, skin abscesses are not a sign of an underlying health problem. However, you are more likely to develop a skin abscess if you have diabetes. Diabetes can cause nerve damage, which can mean you are unable to feel minor cuts and grazes to your skin.

Meticillin-resistant Staphylococcus aureus (MRSA) has been a common cause of skin abscesses in recent years. Read more about MRSA infection.

Internal abscesses

Abscesses that occur in the abdomen (tummy) can be caused by:

  • an infection
  • a tear (rupture) of the intestine
  • an injury
  • surgery to the abdomen

An abscess can develop inside your body when bacteria spread from an existing infection.

For example, a lung abscess can occur as a result of a bacterial infection in your lungs, such as pneumonia (inflammation of the lung tissue), that becomes isolated by the body's immune system. This then develops into a collection of pus (abscess). Bacteria can also spread from other areas of your body through your bloodstream.

Internal abscesses tend to develop in people who have an underlying health problem, such as a brain abscess that occurs after a head wound. Internal abscesses are also more common in people with weakened immune systems, such as those with HIV and AIDS or cancer.

Risk factors

Things that increase the likelihood of an abscess developing include:

  • trauma to a specific area of the body
  • a weakened immune system
  • any material getting into the body
  • a drainage system in the body becoming blocked
  • a build-up of fluid in the tissues of the body
  • a haematoma (collection of blood outside a blood vessel)
  • a PVL-positive strain of bacteria (see above)

Hidradenitis Suppurativa

Hidradenitis suppurativa is a rare inflammatory skin disease that can cause painful abscesses to appear in the armpits and groin.

It is a chronic (long-term) disease that often begins between ages 20-40. It is also more common in females.

The condition is believed to be caused by pores of the apocrine glands (found in the armpits and groin) becoming blocked, but the exact cause is not fully known.

Severe cases of hidradenitis suppurativa can lead to psychological affects or inflammation of the joints (arthritis).

Read more information about hidradenitis suppurativa.

Medical Review: July 15, 2012
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