An abscess begins with an infection of body tissue that may be caused by bacteria, parasites, or a foreign material (such as a splinter). The body uses white blood cells to fight the infection. Pus, which is composed of dead white blood cells, dead tissue, and bacteria, accumulates at the site.
A skin abscess can be seen, and is inflamed, red, and painful. An abscess inside the body may be more serious and difficult to find.