Most abscesses are caused by a bacterial infection.
When bacteria enter your body, your immune system sends infection-fighting white blood cells to the affected area.
As the white blood cells attack the bacteria, some nearby tissue dies, creating a hole which then fills with pus to form an abscess. The pus contains a mixture of dead tissue, white blood cells and bacteria.
Internal abscesses often develop as a complication of an existing condition, such as an infection elsewhere in your body. For example, if your appendix bursts as a result of appendicitis, bacteria can spread inside your tummy (abdomen) and cause an abscess to form.
A small skin abscess may drain naturally, or simply shrink, dry up and disappear without any treatment.
However, larger abscesses may need to be treated with antibiotics to clear the infection, and the pus may need to be drained. This will usually be done either by inserting a needle through your skin or by making a small incision in the skin over the abscess.
Most skin abscesses are caused by bacteria getting into a minor wound, the root of a hair or a blocked oil or sweat gland.
Ensuring that your skin is clean, healthy and largely free of bacteria can help reduce the risk of skin abscesses developing.
You can reduce the risk of bacteria spreading by:
washing your hands regularly
encouraging people in your family to wash their hands regularly
using separate towels and not sharing baths
waiting until your skin abscess is fully treated and healed before using any communal equipment, such as gym equipment, saunas or swimming pools
Don't squeeze the pus out of the abscess yourself, because this can easily spread the bacteria to other areas of your skin. If you use tissues to wipe any pus away from your abscess, dispose of them straight away to avoid germs spreading. Wash your hands after you've disposed of the tissues.
Take care when shaving your face, legs, underarm areas or bikini area to avoid nicking your skin. Clean any wounds immediately and visit your GP or local NHS walk-in centre if you think there may be something trapped in your skin. Don't share razors or toothbrushes.
Abscesses that develop inside an organ or in the spaces between organs can be more difficult to identify than skin abscesses. The symptoms can be vague and there may be no obvious external signs of a problem.
The symptoms of an internal abscess can also vary depending on exactly where in the body the abscess develops. For example, a liver abscess may cause shortness of breath.
General symptoms of an internal abscess can include:
Most abscesses are caused by an infection with staphylococcal bacteria.
When bacteria enter the body, the immune system sends white blood cells to fight the infection. This causes swelling (inflammation) at the site of infection and the death of nearby tissue. A cavity is created, which 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 staphylococcal bacteria produce a toxin called Panton-Valentine leukocidin (PVL) which kills white blood cells. This causes the body to make more cells to keep fighting the infection, and can lead to repeated skin infections.
In rare cases, an abscess may be caused by a virus, fungi or parasites.
When bacteria gets under the surface of your skin, an abscess can form. This can occur anywhere on the body, although skin abscesses tend to be more common in the:
hands and feet
Bacteria can get into your skin and cause an abscess if you have a minor skin wound, such as a small cut or graze, or if a sebaceous gland (oil gland) or sweat gland in your skin becomes blocked.
Abscesses that develop inside the tummy (abdomen) are caused by an infection reaching tissue deeper within the body. This can occur as a result of:
an infection spreading from a nearby area
There are many ways an infection can spread into the abdomen and cause an abscess to develop.
For example, a lung abscess can form after a bacterial infection in your lungs, such as burst appendix can spread bacteria within your abdomen.
In addition to the specific causes mentioned above, things that increase the likelihood of an abscess developing can include:
having a weakened immune system – this could be because of a medical condition such as chemotherapy
However, many abscesses develop in people who are otherwise generally healthy.
See your GP if you think you may have an abscess. There are several tests used to diagnose an abscess, depending on where it's located.
If you have a skin abscess, your GP will first examine the affected area and ask you:
how long you've had the abscess
whether you've injured that area
whether you have any other symptoms
A sample of pus may be taken from your abscess and sent for testing. This allows the specific bacteria causing the abscess to be identified, which can help determine the best way of treating it.
If you've had more than one skin abscess, you may be asked to give a urine sample. This will be tested for glucose, which is a sign of diabetes. People with diabetes have an increased risk of developing skin abscesses.
If you have recurring boils and abscesses, your GP may ask the laboratory to test the bacteria further to see if it's producing Panton-Valentine leukocidin (PVL) toxin. Additional treatments may be recommended, such as a body wash or an antibiotic cream, to stop these bacteria living on the body.
Abscesses that develop inside your body are more difficult to diagnose than skin abscesses because they can't be seen.
Your GP will ask you about your symptoms and any other health conditions you may have. If necessary, they'll refer you to a specialist in hospital.
Abscesses can be treated in a number of different ways, depending on the type of abscess and how large it is.
Some small skin abscesses may drain naturally and get better without the need for treatment. Applying heat in the form of a warm compress, such as a warm flannel, may help reduce any swelling and speed up healing.
However, the flannel should be thoroughly washed afterwards and not used by other people, to avoid spreading the infection.
For larger or persistent skin abscesses, your GP may prescribe a course of antibiotics to help clear the infection and prevent it from spreading.
Sometimes, especially with recurrent infections, you may need to wash off all the bacteria from your body to prevent re-infection (decolonisation). This can be done using antiseptic soap for most of your body and an antibiotic cream for the inside of your nose.
However, antibiotics alone may not be enough to clear a skin abscess, and the pus may need to be drained to clear the infection. If a skin abscess isn't drained, it may continue to grow and fill with pus until it bursts, which can be very painful and can cause the infection to spread or recur.
Incision and drainage
If your skin abscess needs draining, you'll probably have a small operation carried out under local anaesthetic, where you remain awake and the area around the abscess is numbed.
During the procedure, the surgeon makes a cut (incision) in the abscess, to allow the pus to drain out. They may also take a sample of pus for testing.
Once all of the pus has been removed, the surgeon will clean the hole that is left by the abscess using sterile saline (a salt solution).
The abscess will be left open but covered with a wound dressing, so if any more pus is produced it can drain away easily. If the abscess is deep, an antiseptic dressing (gauze wick) may be placed inside the wound to keep it open.
The procedure may leave a small scar.
The pus usually needs to be drained from an internal abscess, either by using a needle inserted through the skin (percutaneous abscess drainage) or with surgery.
The method used will depend on the size of your abscess and where it is in your body.
Antibiotics will usually be given at the same time, to help kill the infection and prevent it spreading. These may be given as tablets or directly into a vein (intravenously).
If the internal abscess is small, your surgeon may be able to drain it using a fine needle. Depending on the location of the abscess, this may be carried out using either a local or general anaesthetic.
Once the abscess has been located, the surgeon drains the pus using the needle. They may make a small incision in your skin over the abscess, then insert a thin plastic tube called a drainage catheter into it.
The catheter allows the pus to drain out into a bag and may have to be left in place for up to a week.
This procedure may be carried out as a day case procedure, which means you'll be able to go home the same day, although some people will need to stay in hospital for a few days.
As with the incision and drainage procedure for skin abscesses, percutaneous drainage may leave a small scar.
You may need to undergo surgery if:
your internal abscess is too large to be drained with a needle
a needle can't get to the abscess safely
needle drainage hasn't been effective in removing all of the pus
The type of surgery you have will depend on the type of internal abscess you have and where it is in your body. Generally, it involves making a larger incision in your skin to allow the pus to be washed out.