An abscess develops when tissue or cells in an area of the body become infected. Your body responds to the infection by trying to kill off the invading bacteria or virus. To fight the bacteria, your body sends white blood cells to the infected areas. These white blood cells begin accumulating in the damaged location and as a result, pus begins to develop. Pus is a thick, fluid-like product that develops from dead white bloods cells, tissue, bacteria, and other invading substances. Abscesses are often painful and warm to the touch.