Pus is a whitish-yellow, yellow, green, or brown-yellow protein-rich fluid called liquor puris that accumulates at the site of an infection. Pus is made of dead, white blood cells that build up as part of the immune response.

When the buildup is on or 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.

Fast facts about pus

  • Pus is a natural result of the body fighting infection.
  • Pus can be yellow, green, or brown, and may in some cases have a foul odor.
  • If pus appears after surgery, contact a doctor immediately.
  • Smaller buildups of pus can be self-managed at home.
  • Larger or less accessible buildups of pus may require surgical intervention and the application of a drainage channel.
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Pus consists of macrophages and neutrophils, sent by the body’s immune system to combat infection.

Pus is the result of the body’s natural immune system automatically responding to an infection, usually caused by bacteria or fungi.

Leukocytes, or white blood cells, are produced in the marrow of bones. They attack the organisms that cause infection.

Neutrophils, a type of leukocyte, have the specific task of attacking harmful fungi or bacteria.

For this reason, pus also contains dead bacteria.

Macrophages, another type of leukocyte, detect the foreign bodies and release an alarm system in the form of small, cell-signaling protein molecules called cytokines.

Cytokines alert the neutrophils, and these neutrophils filter from the bloodstream into the affected area.

The rapid accumulation of neutrophils eventually leads to the presence of pus.

Pus is a sign of infection.

Pus after surgery indicates that there is a post-surgical complication in the form of an infection.

People who detect a discharge of pus following surgery should tell their doctor immediately.

In a patient with weakened immunity, the system may not respond correctly. There may be an infection with no pus.

This can occur if the person:

  • is receiving chemotherapy
  • is taking immunosuppressant medications following an organ transplant
  • has HIV
  • has poorly controlled diabetes.

The doctor will likely prescribe an antibiotic, possibly an ointment for topical application.

Antibiotics help the white blood cells attack the infection. This speeds up the healing process and prevents further complications with the infection.

If there is an abscess, it may need draining, and there may be a special incision care program.

The whitish-yellow, yellow, yellow-brown, and 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.

A bacterium called Pseudomonas aeruginosa (P. aeruginosa) 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.

The underlying reason for the pus is the main target for treatment, and the strategy will depend on the cause.

Home treatments

If pus builds up close to the surface of the skin, such as in pimples, medical intervention is not required. The pus may be drained at home.

Soaking a towel in warm water and holding it against the infected pus for 5 minutes will reduce the swelling and open up the pimple or skin abscess for a faster healing process.

Clinical intervention

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Pus can sometimes gather in the form of an localised abscess

Patients who have undergone surgery and who notice a discharge of pus should not apply over-the-counter antibiotic cream, alcohol, or peroxide.

They should contact their doctor or surgeon.

Large abscesses or those that are difficult to access should also be treated by a clinician.

The doctor will attempt to create an opening so that the pus can ooze out, or evacuate. Medications may also be necessary.

Treatment to remove pus may be necessary in the following cases:

Recurring otitis media, or middle ear inflammation: This can lead to recurring excess fluid in the middle ear. A specialist may need to insert a grommet in the eardrum to help evacuate this fluid.

Grommets are small plastic tubes that are inserted into the ear.

As well as draining fluid, grommets also allow air into the space behind the ear drum, reducing the risk of a future buildup of fluid.

Abscesses: Antibiotics may treat smaller abscesses, but sometimes they are not effective.

The doctor may need to insert a drainage-channel to help evacuate the pus rapidly.

A surgical drain may be used to assist with removal of pus.

This is a tube-like structure that may or may not be attached to a suction pump.

Septic arthritis: If an infection develops in a joint, or passes from another part of the body to a joint, pus and general inflammation can occur in the joint.

After identifying which bacterium is causing the infection, the doctor will decide on a course of intravenously administered antibiotics. This may last many weeks.

Joint drainage may be necessary to remove pus.

A flexible tube with a video camera at its tip, called an arthroscope, is placed into the joint through a tiny incision.

This device guides the doctor to insert suction and drainage tubes around the joint to draw out the infected synovial fluid.

Arthrocentesis is a different procedure.

It involves removing the infected fluid with a needle. The extracted fluid is examined for bacteria, and the arthrocentesis repeated every day until there are no more bacteria in the fluid.