Whenever an area of the body becomes infected with accumulation of pus, the condition is called an abscess. A large collection of pus in the chest cavity is called empyema. The abscess forms because pus-forming germs like the staphylococci or streptococci, or less often others form poisons which destroy the cells. Inflammation occurs and the white blood cells or leukocytes come into the area and help to take up and liquefy the material. The white blood cells give the pus a creamy appearance.

Eventually the wall of inflammation around the abscess thins out so that the pus may burst through. Thus a boil, which is a form of abscess, "points" or "comes to a head." Physicians consider it safest to open the abscess with a sterilized knife after cleaning the area, so that the pus may be cleanly and wholly removed without damaging tissue unnecessarily.

Should the abscess break into the abdominal cavity, it might set up general infection or peritonitis. If an abscess breaks into a large blood vessel, the infection may be quickly spread through the whole body, causing sepsis. In control of the infected area antiseptics may be applied or there may be injections of the sulfonamide drugs or penicillin or other suitable antibiotics.