An abscess is a collection of pus. Pus is a thick fluid that usually contains white blood cells, dead tissue and germs (bacteria). The pus may be yellow or green and may have a bad smell. The usual cause of an abscess is an infection with bacteria. Certain bacteria are more likely to be ‘pus-forming’ as they make chemicals (toxins) that can damage the body’s tissues. These include Staphylococcus aureus and Streptococcus pyogenes. The infection causes the immune system to set off 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 and the pus can’t get out.
Where do abscesses form?
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. A gland just below the skin at the entrance to the vagina can become infected and develop into a Bartholin’s abscess. Occasionally, women who are breast-feeding can develop an infection in the breast that becomes a breast abscess. 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 abscess inside the body usually happens because of another condition. Infection in the liver, for example, can result in a liver abscess. An ultrasound scan or other types of scan can confirm a suspected abscess. If infection occurs in the gums or teeth a dental abscess can develop.
Who develops abscesses?
Most skin abscesses occur in people who are otherwise well. There is often no underlying cause and usually no further problems 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 (an injury in which the outer covering of the brain is pierced), etc.
The main treatment is to drain away the pus from the abscess. For a skin abscess, this involves a small operation to cut the top of the skin and allow the pus to drain. A local anaesthetic will usually be used. A scar will form as the skin heals. If the abscess is deep, a small piece of gauze (antiseptic wick) may be put in the drainage hole. This stops the hole from sealing over before all of the pus has drained and the cavity has shrunk.
A more sophisticated operation is needed to drain an abscess from inside the body. The techniques vary, depending on the site of the abscess. Sometimes a tube will be left in the hole to drain the pus.
Medicines called antibiotics may also be prescribed, especially if there is infection in the skin (cellulitis). However, they are often not able to treat an abscess on their own. See separate leaflet called Cellulitis and Erysipelas for more details.