What Is Pus?

Editor's Choice
Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: Dermatology
Article Date: 17 Aug 2012 - 10:00 PST


Pus is a protein-rich fluid called liquor puris, usually whitish-yellow, yellow, or yellow brown in color. Pus consists of a buildup of dead leukocytes (white blood cells) from the body's immune system in response to infection. It accumulates at the site of inflammation. When the buildup is on or very near the surface of the skin it is called a pustule or pimple. An accumulation of pus in an enclosed tissue space is called an abscess.

Pus is a fluid that had filtered from the circulatory system into an area of inflammation caused by an infection; an exudate.

According to Medilexicon's medical dictionary, Pus is:

"A fluid product of inflammation, consisting of a liquid containing leukocytes and the debris of dead cells and tissue elements liquefied by the proteolytic and histolytic enzymes (leukoprotease) that are elaborated by polymorphonuclear leukocytes."

A patient with conjunctivitis and its hallmark sign of pus

What causes the accumulation of pus?

The presence of pus is the result of our body's natural immune system responding to an infection, usually caused by bacteria or fungi. When the body detects an infection, our immune system immediately reacts to get rid of it and limit the damage.

Leukocytes (white blood cells), which are produced in the marrow of bones, attack the organism that are causing the infection. Neutrophils, a type of leukocyte, have the specific task of attacking harmful fungi or bacteria.

Another type of leukocyte, called macrophages, detect the foreign bodies and release an alarm system in the form of small cell-signaling protein molecules called cytokines. Cytokines alert the neutrophils, which filter from the bloodstream into the affected area.

Experts say that the neutrophils are within the affected area about an hour after an infection starts. The rapid accumulation of neutrophils eventually leads to the presence of pus - a large quantity of dead neutrophils.

Puss after surgery

Pus is a sign of infection. This is good and bad news:

• Good news - it means that the body's immune system is fighting the infection.


• Bad news - it means that there is a post-surgical complication - an infection.

If the patient has a weakened immune system, which may occur if they are being administered chemotherapy, are organ transplant recipients and taking immunosuppressant medications, are HIV positive, or have poorly controlled diabetes, the immune system may not have responded properly and there may be an infection with no pus.

People who have undergone surgery and detect the discharge of pus should tell their doctor immediately. The doctor will likely prescribe an antibiotic, ointments and recommend a special incision care program. Antibiotics help the white blood cells attack the infection, speed up the healing process, and prevent an infection complication.

Patients who have undergone surgery and are discharging pus should not slather the incision with antibiotic cream, use alcohol or peroxide. They should see their doctor or surgeon.

Why does pus have a yellowish or greenish color?

The whitish-yellow, yellow, yellow-brown, and even greenish color of pus is the result of an accumulation of dead neutrophils.

Pus can sometimes be green because some white blood cells produce a green antibacterial protein called myeloperoxidase. Pseudomonas aeruginosa, a bacterium, produces a green pigment called pyocyanin. Pus from infections caused by P. aeruginosa is particularly foul-smelling. If blood gets into the affected area the yellowish or greenish color may also have tinges of red.

What are the treatment options for pus?

The doctor will attempt to create an opening so that the pus can ooze out - doctors usually say "to evacuate".

Ubi pus, ibi evacua - this Latin adage is a medical term which means "Where pus, there evacuate" ("if there is pus, let it out"). This aphorism refers to what a doctor should do when there is pus in the body - create an opening so that it can leave the body.

Recurring otitis media (middle ear inflammation) - some children have excess fluid within the middle ear; a problem which may recur. An ear/nose and throat specialist, an otorhinolaryngologist, may recommend inserting a grommet in the eardrum to help evacuate excess fluid.

Abscesses - sometimes antibiotics are not very effective in treating an abscess; the active ingredient may find it hard to get into the abscess, or the environment may have a low pH. The doctor may insert a drainage-channel to help evacuate the pus rapidly.

Septic arthritis - an extremely painful infection in a joint which originated from another infected part of the body (in some cases only the joint is infected). The affected joint has a considerable accumulation of pus and general inflammation.

• The doctor will first identify which bacterium is causing the infection and decide on a course of intravenously administered antibiotic. The antibiotics course may last several weeks.


• Joint drainage - a flexible tube with a video camera at its tip, an arthroscope, is placed in the joint through a tiny incision. The doctor then inserts suction and drainage tubes around the joint to suck out the infected synovial fluid. Arthrocentesis refers to the removal of the infected fluid with a needle. The extracted fluid is examined for bacteria - the arthrocentesis is repeated every day until there is no more bacteria in the fluid.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

• Additional
• References
• Citations