Pus is gooey yellow, green or brown liquid that is product of an infection in the body.  Pus is made of a combination of white blood cells, dead and damaged body tissue, bacteria, blood, water, proteins and other dbris.  When bacteria invade the body, white blood cells rush to the area to fight!  The battle between white blood cells and germs causes inflammation and damage to the surrounding tissues.

Much of the bacteria in pus is still alive and able to reproduce.  Therefore pus must either be removed by the body's scavenger cells (i.e., macrophages), absorbed into the blood stream, or drained to the outside of the body.

A collection of pus inside the body is called an abscess.  An abscess that forms under the skin may cause a boil.  Several boils connected by tunnels under the skin is called a carbuncle.

See article on skin bacterial infections...