An abscess is a collection of pus collected in a cavity formed by the tissue on the basis of an infectious process (usually caused by bacteria or parasites) or other foreign materials (e.g. bullet wounds). It is a defensive reaction of the tissue to prevent the spread of infectious materials to the other parts of the body.

The organisms or foreign materials that gain access to a part of tissue kill the local cells, release toxins and trigger an inflammatory response by drawing huge amounts of white blood cells to the area and increasing the regional blood flow. So, pus is a collection of local dead tissue cells, white blood cells, infecting organisms or foreign material and toxins released by both organisms and blood cells. The final structure of the abscess is an abscess wall that is formed by the adjacent healthy cells in an attempt to build a barrier around the pus that limits the infected material from neighbouring structures.

The cardinal symptoms and signs of any kind of inflammatory process are redness, heat, swelling and pain. Abscesses may occur in any kind of solid tissue but most frequently on skin surface (where they may be superficial pustules or deep skin abscesses), in the lungs, brain, kidneys and tonsils. Major complications are spreading of the abscess material to adjacent or remote tissues and extensive regional tissue death (gangrene). Abscesses in most parts of the body rarely heal themselves, so prompt medical attention is indicated at the first suspicion of an abscess.

The treatment of first choice is the surgical drainage of the abscess. It is important to note that antibiotic therapy alone without surgical drainage of the abscess is seldom effective. However, in critical areas where surgery presents a high risk (such as the brain), surgery may be delayed or used as a last resort. The drainage of the lung abscess may be performed by giving the patient a certain position that enables the contents to be discharged via the respiratory tract. After surgical drainage, antibiotics are usually used to control the infection. Warm compresses and elevation of the limb may be beneficial for skin abscess.

Perianal abscesses are seen in patients with inflammatory bowel disease, Crohn's disease, or diabetes. Often the abscess will start as an internal wound caused by ulceration or hard stool. This wound typically becomes infected as a result of the normal presence of feces in the rectal area, and then develops into an abscess. This often presents itself as a lump of tissue near the anus which grows larger and more painful with the passage of time.

See also

• sterile abscess