What is an abscess and what causes it?

An abscess is a collection of pus. Pus is a thick fluid that usually contains white blood cells, dead tissue and bacteria (germs). The usual cause of an abscess is an infection with bacteria. Certain bacteria are more likely to be 'pus forming' as they make toxins (chemicals) that can damage the body's tissues. These include: Staphylococcus aureus and Streptococcus pyogenes. The infection causes the immune system to activate white blood cells and chemicals to fight the bacteria. In this 'battle' some tissue dies. A cavity forms and fills with pus. The cavity becomes bigger if the infection continues.

Where do abscesses form?

• The skin. Most abscesses form just under the skin. A boil is the most common example. In this case, a hair root becomes infected and develops into a small abscess. The skin next to the anus is another common area for an abscess to develop. The symptoms of a skin abscess include: swelling, redness, pain, and warmth over the affected area.
• Inside the body. An abscess sometimes forms inside the body within an organ or in a space between organs. Various symptoms may occur, depending on the site of the abscess. An ultrasound scan, or other types of scan, can confirm a suspected abscess.

Who gets abscesses?

Most skin abscesses occur in people who are otherwise well. There is often no underlying cause, and no further problems usually occur once it has gone. Your doctor may check your urine for sugar, as abscesses tend to occur more often in people with diabetes. Recurring skin abscesses may be the first indication of a problem with your immune system.

An abscess inside the body usually occurs in people who are ill with other problems, or in people whose immune system is not working well. For example: a lung abscess may form following a bout of pneumonia; a brain abscess may form after a penetrating head wound, etc.

What is the treatment for an abscess?

Antibiotics are usually prescribed and the pus usually needs to be drained away. For a skin abscess, this involves a small operation to cut the top of the skin and allow the pus to drain. A scar will form as the skin heals. A more sophisticated operation is needed to drain an abscess from inside the body. The techniques vary, depending on the site of the abscess.

What would happen if an abscess were not treated?

A skin abscess would normally eventually burst on to the skin surface and let out the pus. This may be after it becomes larger and more painful. So, antibiotics and surgical drainage are usually best. However, a small boil may burst and heal without treatment. An untreated abscess inside the body is usually very serious. You are likely to become very ill and treatment is usually needed.