Pus: What is it and why does it happen?

Pus: What is it and why does it happen?

Pus is a protein-rich whitish-yellow, yellow, or brown-yellow fluid called liquor puris which accumulates at the site of an infection.

It is a buildup of dead, white blood cells that form when the immune system of the body responds to the infection.

If the buildup is on or near the skin’s surface it is called a pustule or pimple. An accumulation of pus in a space surrounding the tissue is called an abscess.

Important 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.


Pus cells
Pus consists of macrophages and neutrophils, sent by the body’s immune system to combat infection.

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

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

A type of leukocyte, the neutrophils have the specific task of attacking harmful fungi or bacteria.

Therefore, pus contains dead bacteria, too.

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

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

Eventually the rapid accumulation of neutrophils leads to the presence of pus.

Pus after surgery

Pus is an Infection Sign.

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

People who notice a discharge of pus after an operation will immediately inform their doctor.

The system can not react correctly in a patient with the weakened immunity. There may be a no-pus infection.

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 probably will prescribe an antibiotic, possibly an ointment for topical use.

Antibiotics aid in attacking the infection by white blood cells. This speeds up the healing process and avoids further infectional complications.

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

Why is pus yellow?

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

Since certain white blood cells contain a green antibacterial protein called myeloperoxidase, Pus can be green.

Pseudomonas aeruginosa (P. aeruginosa) is a bacterium that produces a green pigment called pyocyanin.

Pus from infections caused by P. aeruginosa is particularly foul-smelling.

If blood comes into the affected area, red tinges may also be present in the yellowish or greenish colour.


The primary goal for treatment is the underlying reason for the pus, and the approach may focus on the cause.

Home treatments

If pus builds up close the skin surface, like in pimples, medical intervention is not needed. At home, the pus can get drained.

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

Clinical intervention

Pus can sometimes gather in the form of an localised abscess
Pus can sometimes gather in the form of an localised abscess

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

They should contact their surgeon or doctor.

A clinician may also treat large abscesses, or those that are difficult to access.

The doctor will try to create an opening that allows the pus to ooze out, or evacuate. Medications may also be needed.

In the following cases treatment to remove pus can be necessary:

Recurring otitis media, or inflammation of the middle ear: This can cause excess fluid in the middle ear to recur. In order to help remove this fluid, a specialist can need to insert a grommet into the eardrum

Grommets are tiny plastic tubes that are put into the ear.

In addition to draining fluid, grommets also allow air into the space behind the ear drum, thus reducing the risk of a future fluid buildup.

Abscesses: Antibiotics can treat smaller abscesses but they may not be effective at times.

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

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

This is a tube-like structure which may or may not be mounted on a suction pump.

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

After determining which bacterium causes the infection, the doctor will decide on a course of antibiotics given by intravenous administration. This could last for several weeks.

It can require joint drainage to remove the pus.

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

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

Arthrocentesis is another treatment.

It involves removing a needle to the infected fluid. The extracted fluid is examined for bacteria, and the arthrocentesis is repeated every day until the fluid no longer contains any bacteria.