Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection.[1][2] An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection of pus within or beneath the epidermis is known as a pustule, pimple, or spot.

An abscess is an enclosed collection of pus.
SpecialtyInfectious disease

Pus consists of a thin, protein-rich fluid, historically known as liquor puris,[3][4] and dead leukocytes from the body's immune response (mostly neutrophils).[5] During infection, macrophages release cytokines which trigger neutrophils to seek the site of infection by chemotaxis. There, the neutrophils release granules which destroy the bacteria. The bacteria resist the immune response by releasing toxins called leukocidins.[6] As the neutrophils die off from toxins and old age, they are destroyed by macrophages, forming the viscous pus.

Bacteria that cause pus are called pyogenic.[6][7]

Although pus is normally of a whitish-yellow hue, changes in the color 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. Green, foul-smelling pus is found in certain infections of Pseudomonas aeruginosa. The greenish color is a result of the bacterial pigment pyocyanin that it produces. Amoebic abscesses of the liver produce brownish pus, which is described as looking like "anchovy paste". Pus from anaerobic infections can more often have a foul odor.[8]

In almost all cases when there is a collection of pus in the body, a clinician will try to create an opening to drain it. This principle has been distilled into the famous Latin aphorism "Ubi pus, ibi evacua" ("Where there is pus, evacuate it").

Some disease processes caused by pyogenic infections are impetigo, osteomyelitis, septic arthritis, and necrotizing fasciitis.[9]

Eye with conjunctivitis exuding pus
Duodenoscopy image of hepatopancreatic ampulla with pus exuding from it, indicative of cholangitis

Pyogenic bacteria

A great many species of bacteria may be involved in the production of pus. The most commonly found include:[10]

Staphylococcus aureus bacteria is the most common cause of boils.

Historical terminology

In the pre-asepsis era, surgeon Frederick Treves (1853–1923) wrote, "Practically all major wounds suppurated. Pus was the most common subject of converse [among surgeons], because it was the most prominent feature in the surgeon's work. It was classified according to degrees of vileness."[11]:347 But pus of the right kind was considered desirable.[12]:80 "If a patient was lucky ... a thick cream-colored odorless fluid would appear within five or six days"; such "laudable" pus was considered "a sure sign that the wound would heal"[11]:344 because it meant "Nature has put up a bold fight against the invader".[13] "On the other hand, if the pus gradually became watery, blood tinged and foul smelling, it was designated 'sanious'[14] [or 'ill-conditioned'][15] and the wound condition was considered unfavorable".[14] It later came to be understood that "laudable" pus generally implied an invasion of relatively benign staphylococcus, while "ill-conditioned" pus usually meant the more dangerous streptococcus was present.[11]:345[14]:247

See also


  1. "Pus". dictionary.reference.com. Retrieved 2008-08-18.
  2. "Pus – What Is Pus?". medicalnewstoday.com. Retrieved 2016-08-19.
  3. British Medical Journal. British Medical Association. 1917. pp. 751–754.
  4. Society, Louisiana State Medical (1846). Journal. p. 251.
  5. Barer, M.R. (2012). "The natural history of infection". Medical Microbiology. Elsevier. pp. 168–173. doi:10.1016/b978-0-7020-4089-4.00029-9. ISBN 978-0-7020-4089-4.
  6. Madigan, Michael T. and Martin, John M. Brock Biology of Microorganisms 11th ed. Pearson Prentice Hall. US. 2006: 734
  7. "pyogenic" at Dorland's Medical Dictionary
  8. Topazian RG, Goldberg MH, Hupp JR (2002). Oral and maxillofacial infections (4 ed.). Philadelphia: W.B. Saunders. ISBN 978-0721692715.
  9. "Infections Caused by Common Pyogenic Bacteria", Dermatopathology, Berlin Heidelberg: Springer, 2006, pp. 83–85, doi:10.1007/3-540-30244-1_12, ISBN 978-3-540-30245-2
  10. Thompson, Alexis; Miles, Alexander (1921). "Pyogenic Bacteria". Manual of Surgery (6th ed.). Oxford Medical Publications. OCLC 335390813.
  11. Nuland, Sherwin B. (2011). Doctors: The Biography of Medicine. Knopf Doubleday. ISBN 978-0-307-80789-2.
  12. Van Hoosen, Bertha (Autumn 1947). "A Woman's Medical Training in the Eighties". Quarterly Review of the Michigan Alumnus: A Journal of University Perspectives. University of Michigan Libraries: 77–81. UOM:39015006945235.
  13. Scott, William (1922). An indexed system of veterinary treatment. Chicago: Eger. p. 603.
  14. Schneider, Albert (1920). Pharmaceutical bacteriology (2nd ed.). P. Blakiston. p. 247.
  15. Williams, Charles J. B. (1848). Principles of Medicine: Comprising General Pathology and Therapeutics, and a Brief General View of Etiology, Nosology, Semeiology, Diagnosis, and Prognosis: With Additions and Notes by Meredith Clymer. Churchill. p. 306.
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