An abscess is an accumulation of pus, usually caused by a bacterial infection. When bacteria invade healthy tissue, the infection spreads through the area.
Some cells die and disintegrate, leaving spaces where fluid and infected cells accumulate.
White blood cells, the body's defenders against infection, move into these spaces, and after engulfing bacteria, they die. The dead white blood cells accumulate as pus, a creamy substance that fills the area. As pus collects, healthy tissue is pushed aside. If an abscess ruptures internally, the infection may spread either inside the body or under the skin surface, depending on the location of the abscess. A bacterial infection may lead to an abscess in several ways.