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. The white blood cells (polymorphs) kill them and then die. As the white blood cells attack the bacteria, inflammation (swelling) and death of nearby tissue may occur, causing a hollow to form.
The hollow 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
See the Health A-Z topic about Staphylococcal infections for more information.
PVL Staphylococcus aureus
Staphylococcus aureus is a type of bacterium found on the surface of healthy skin. 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
- the groin
- inside the nostrils
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. They can also cause more serious conditions:
- Septicaemia is blood poisoning caused by bacteria multiplying in the blood.
- Pneumonia is swelling (inflammation) of the lungs caused by an infection. Pus collects in the airways and is coughed up as mucus.
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 occur 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 any minor cuts and grazes to your skin.
Meticillin-resistant Staphylococcus aureus (MRSA) has been a common cause of skin abscesses in recent years.
See the Health A-Z topic about MRSA infection for more information.
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 occur inside your body when bacteria spread from an existing infection.
For example, a lung abscess can occur as a result of a bacterial infection that is already present in your lungs, such as pneumonia (inflammation of the lung tissue). Bacteria can also spread from other areas of your body through your bloodstream.
Internal abscesses tend to occur in people who have an underlying health problem, such as a brain abscess that develops after a severe head wound. Internal abscesses can also sometimes develop in people with damaged immune systems, such as those with HIV and AIDS or those who are having chemotherapy treatment for cancer.
Risk factors
Risk factors that are known to 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)
