Something that creates pus is called suppurative, pyogenic, or purulent. If it creates mucus as well as pus, it is called mucopurulent.
Pus consists of a thin, protein-rich fluid, known as liquor puris, and dead cells, which are part of the body's innate immune response. Pus can also appear visibly from pimples. Neutrophils are produced in the bone marrow and released into the blood. When the need to fight infection arises, they move to the site of infection by a process known as chemotaxis, usually triggered by cytokines released from macrophages that sense invading organisms. At the site of infection, they engulf and kill bacteria. Eventually, the neutrophils die, and these dead cells are then phagocytosed by macrophages, which break them down further. Pus, therefore, is the viscous material composed of these dead neutrophils.
When seen in a wound or dry skin, pus indicates the area is infected and should be cleaned with antiseptic.
Despite normally being of a whitish-yellow hue, changes in the color of pus can be observed under certain circumstances. Pus is sometimes green because of the presence of myeloperoxidase, an intensely green antibacterial protein produced by some types of white blood cells. Blue pus is found in certain infections of Pseudomonas aeruginosa as a result of the pyocyanin bacterial pigment it produces; amoebic abscesses of the liver, meanwhile, produce brownish pus. Pus might have a reddish tint to it after mixing with blood. Pus can also have a foul odor.