What is Pus?

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Pus, also known as liquor puris, is a thick yellowish, whitish, or greenish fluid made up of dead white blood cells, dead tissues, and dead bacteria or fungi. It is produced as part of the body's response to an infection. Pus is usually odorless but can emit a foul odor if the infection is severe.

Pus can occur with common skin conditions like acne or when a break in the skin allows germs to enter underlying tissues (such as might occur with a cut or surgical incision). Surgeries or diseases like appendicitis or diverticulitis can also cause infections in deeper tissues that lead to pus.

This article discusses the causes of pus and how it develops in different parts of the body. It also describes the diagnosis and treatment of infections associated with pus, and when it is time to see a healthcare provider.

Pimple near the mouth

Photo: Angela Palmer

 

How Does Pus Form?

Pus is a byproduct of your immune system's fight against an invader, mostly commonly bacteria or certain fungi.

When an infection occurs, the immune system will send different white blood cells (leukocytes) to fight the infection. These include macrophages and dendritic cells that surround and absorb the invader, thereafter killing them through a process known as phagocytosis-induced apoptosis. This is when white blood cells "commit suicide" to kill the invader they have absorbed.

In the aftermath, dead white blood cells, dead bacteria or fungi, and dead tissues will start to accumulate, resulting in pus.

Pimple vs. Pustule vs. Abscess

A collection of pus within or just beneath the outermost layer of skin (epidermis) is called a pustule or pimple. The accumulation of pus within an enclosed space in deeper tissues is known as an abscess.

Pus is usually an opaque, white-yellow color. It can also be brown or green. Different colors of pus can hint at different infections.

What Does Pus Do?

Pus doesn't serve any function. It is simply the byproduct of the immune defense.

With pustules, your body may be able to slowly absorb and break down the pus without treatment. The pustule may also drain naturally, eventually shrinking and drying up.

Smaller abscesses near the surface of the skin may also do the same, but larger ones or those inside the body most often needed to be drained.

Skin Infections

Pus is commonly accompanied by other symptoms of an infection, including pain, tenderness, redness, swelling, and heat. Severe skin infections can cause also fever with chills.

There are many skin conditions that can cause pus, some of which include:

  • Acne: A common skin condition that occurs when hair follicles become clogged will sebum (a natural skin oil), dead skin cells, and bacteria (most commonly Propionibacterium acnes).
  • Carbuncles: These are a type of abscess that occurs in deeper skin tissues.
  • Folliculitis: This is a condition characterized by inflammation of hair follicles, most commonly caused by bacteria called Staphylococcus aureus.
  • Furuncles: Also known as boils, these are a type of abscess that occurs in hair follicles.
  • Superficial surgical site infection (SSI): A superficial SSI occurs when an incision near the surface of the skin is contaminated with bacteria, such as during a mole removal.
  • Wound contamination: Any break in the skin can cause pus if the wound is not treated properly.

Internal Infections

Pus-filled abscesses can form internally, such as in the mouth, internal organs, or deeper tissues. This can be a result of an injury, surgical complication, or bacterial or fungal infection that becomes systemic (affects the whole body).

There are many different causes of internal abscesses, examples of which include:

  • Abscessed tooth: This is a dental infection in or near the root of a tooth.
  • Appendicitis: The inflammation of the appendix can cause abscesses and other severe symptoms prior to and after the rupture.
  • Brain abscess: This is a rare accumulation of pus in the brain caused by a bacterial or fungal infection.
  • Deep surgical site infection (SSI): A deep SSI occurs when tissues are accidentally infected due to breaches in sterile surgical practices.
  • Diverticular disease: This is caused by abnormal pouches that develop in the intestine which can become infected due to ruptured tissues and bacteria in stool.
  • Empyema: This is a collection of pus in the space between the lungs and the chest wall. It can be a complication of bacterial pneumonia or lung surgery.
  • Peritonsillar abscesses: These are abscesses at the back of the throat or behind the tonsils that occur as a result of strep throat or tonsillitis.
  • Septic arthritis: This is a serious joint infection that can form after bacteria travels through the bloodstream and infects a joint.
  • Urinary tract infection (UTI): Pus in urine, called pyuria, is a sign of a serious infection of the urinary tract.

Preventing Pus From Developing

There are things you can do to reduce your risk of developing an infection with pus:

  • Wash cuts and other wounds thoroughly with soap and water.
  • Wash your hands thoroughly and regularly.
  • Avoid touching wounds. Keep them covered with a clean bandage or dressing, changing them when needed.
  • You can lightly apply an antibiotic ointment for superficial cuts.
  • When the wound is amply closed, remove the bandage to air the wound and prevent the underlying tissue from getting mushy.
  • Don't squeeze pimples. Instead, apply a warm compress several times a day to help them drain.

Before and After Surgery

Between 1% and 3% of people who have surgeries develop an SSI, according to the Centers for Disease Control and Prevention (CDC).

There are steps you can take before and after any procedure to reduce your risk of an SSI.

Before Surgery
  • The night before surgery, wash your whole body with soap in the bath or shower.

  • Do not shave near the surgical site as the can irritate the skin and increase your risk of infection. (if shaving is needed, the surgical staff will do it for you.)

After Surgery
  • Family or friends should wash their hands before visiting and should not touch your wound.

  • Follow the wound care instructions provided by your surgeon.

  • Always wash your hands before and after caring for the wound.

  • Inspect your incision daily for signs of infection.

  • Do not scrub your incision or use antibiotic ointment, alcohol, or peroxide unless your healthcare provider tells you to.

Clear or blood-tinged drainage from a surgical wound is considered normal unless there is a large amount of it. Wound drainage can last anywhere from one to five weeks, depending on the extensiveness of the procedure.

However, if you have cloudy, creamy, or foul-smelling drainage, call your healthcare provider immediately as this is a sign of an infection.

Pus Treatment

If an infection causes pus, it more often than not requires treatment. Depending on the severity of the infection, this might include:

  • Antibiotics
  • Drainage
  • Surgical debridement
How to care for incisions with pus.

 Verywell / Laura Porter

Antibiotics

Bacterial infections are treated with antibiotics.

Topical antibiotics applied to the skin are used for uncomplicated, superficial infections. Oral antibiotics taken by mouth are used for more severe infections. LIfe-threatening or systemic infections may require intravenous antibiotics delivered through a vein.

Your healthcare provider may collect a sample of pus and send it to a lab to determine which type of bacteria you have using a culture and sensitivity test. The test can determine which antibiotic may be most effective at clearing your infection.

Topical antibiotics can also be used for superficial fungal infections, mainly to prevent a secondary infection. This is when a fungal skin infection causes a break in the skin that allows bacteria to enter.

Fungal infections are directly treated with antifungals.

Drainage and Tissue Removal

In some cases, an abscess drainage may be needed to clear pus. In such cases, if pus is not cleared, the infection may be harder to resolve. At the same time, the infection may spread into the bloodstream, causing a potentially life-threatening reaction known as sepsis.

External abscesses may be lanced (cut) or drained with a need and syringe.

For internal abscesses, the surgeon will start by draining the pus with the needle. A thin plastic tube, called a drainage catheter, may also be inserted into the space to drain pus into a bag. If the abscess is large, the catheter may have to be left in place for up to a week.

Surgical debridement may be needed for large abscesses to remove dead tissues (as dead tissues are hotbeds for infection). It involves thoroughly cleaning the wound and removing any necrotic (dead) or infected tissues along with any debris.

When to See a Healthcare Provider

Let your healthcare provider know if you experience a pus-like discharge from any part of the body. This is particularly important if you recently had surgery.

Seek urgent medical care if you have any of the following symptoms following surgery or the treatment of a wound:

Ignoring an infection can lead to more scarring and a longer recovery. It can also put you at risk of serious and even life-threatening complications, such as sepsis.

Summary

Your body produces pus as a response to infection. It is made up of dead white blood cells, bacteria or fungi, and tissue debris.

It can occur with common skin infections like acne or when bacteria enter hair follicles or cuts. It can develop in deeper tissues that are contaminated during surgery or by local or systemic infections.

Proper wound care can prevent pus from developing. If an infection causes pus, treatment may include antibiotics, pus drainage, and possibly surgical debridement.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  3. University Health News. Pus: an unmistakable sign of infection.

  4. Centers for Disease Control and Prevention. Surgical site infections (SSIs).

  5. Bajracharya GR, Esa WAS, Mao G, Leung S, Cohen B, Maheshwari K, et al. Regional analgesia and surgical site infections after colorectal surgery: a retrospective cohort analysis. Braz J Anesthesiol. 2022 Jul 5:S0104-0014(22)00074-4. doi:10.1016/j.bjane.2022.06.002.

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By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.