An abscess is a collection of pus in any part of the body. In most cases, the area around an abscess is swollen and inflamed.
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Abscesses occur when an area of tissue becomes infected and the body's immune system tries to fight it. White blood cells (WBCs) move through the walls of the blood vessels into the area of the infection and collect in the damaged tissue. During this process, pus forms. Pus is the buildup of fluid, living and dead white blood cells, dead tissue, and bacteria or other foreign substances.
Abscesses can form in almost any part of the body. The skin, under the skin, and the teeth are the most common sites. Abscesses may be caused by bacteria, parasites, and foreign substances.
Abscesses in the skin are easy to see. They are red, raised, and painful. Abscesses in other areas of the body may not be seen, but they may cause organ damage.
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Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.