Most abscesses are caused by a bacterial infection. The way that bacteria gets into your body to cause an abscess differs between skin abscesses and internal abscesses.
How bacteria cause an abscess
When a type of bacteria is able to enter your body, your immune system tries to fight it off by sending white blood cells to the affected area. As your white blood cells attack the bacteria, some of the tissue at the site of the infection dies, causing a hollow to form.
The hollow fills with pus to form an 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.
Some types of bacteria, such as Staphylococcus aureus, are more likely to result in large amounts of pus than others. This is because it produces toxins that damage your body’s tissue and break it down, creating pus.
See the ‘useful links’ section for more information about Staphylococcal infections.
Causes of skin abscesses
Bacteria can cause a skin abscess when it is able to get under the surface of your skin. This may occur if you have a minor skin wound, such as a small cut, or graze, or if an oil (sebaceous), or sweat gland, in your skin becomes blocked.
Boils are the most common type of skin abscess, and occur when bacteria enters the root of a hair on your skin.
In most cases, skin abscesses occur on their own, and are not a sign of an underlying health problem.
However, you are more likely to develop a skin abscess if you have diabetes. This is because diabetes can cause damage to your nerves, which can mean that you do not feel any minor cuts and grazes to your skin. Bacteria can then enter your skin and cause an abscess.
Causes of internal abscesses
An abscess can occur inside your body when bacteria spread from an existing infection. A lung abscess can be caused by a bacterial infection that is already present in your lungs, such as pneumonia (inflammation of the tissues of your lungs).
Bacteria can also spread from other areas of your body through your bloodstream. For example, pneumonia can cause an abscess in your brain if bacteria gets into your blood and reaches your brain.
However, internal abscesses such as these are usually very rare. They tend to occur in people who have an underlying health problem (such as a brain abscess that develops following a severe head wound). Internal abscess can also sometimes develop in people with damaged immune systems, such as those with HIV, or AIDS, or those who are having chemotherapy treatment for cancer.
