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What is pus?

Pus is a thick, whitish to yellowish material composed primarily of dead cells that generally forms as a by-product of bacterial infections. The inflammatory cells that participate in the body’s immune response at the site of an infection eventually degrade and die, creating the substance known as pus. One of the most common types of bacteria that cause pus formation is Staphylococcus aureus, although any bacterial infection may produce pus. An infection that leads to the production of pus is called a purulent infection.

When pus forms within enclosed spaces in the tissues, it causes abscesses. When it forms on the skin surface, it causes lumps known as pustules or pimples. Pus can also form when infections develop in internal organs, such as the bones, brain, lungs, and gastrointestinal tract.

Because the formation of pus usually indicates a bacterial infection, people with conditions that weaken the immune system have a higher risk of infection and subsequent pus formation.

The formation of pus generally signals a bacterial infection, which may be a serious condition. Seek immediate medical care (call 911) if pus formation is associated with other symptoms of severe bacterial infections such as high fever, headache, severe pain, difficulty breathing, or confusion or loss of consciousness for even a brief moment.

Seek prompt medical care if your pus is persistent or causes you concern.


What other symptoms might occur with pus?

Pus formation is typically caused by a bacterial infection and may accompany other symptoms, which vary depending on the underlying disease, disorder or condition.

Localized symptoms that may occur along with pus

Pus may accompany localized symptoms including:

  • Lump or mass felt beneath the skin
  • Oozing or leakage of fluid
  • Pain or tenderness
  • Skin redness or the presence of red streaks on the skin
  • Skin warmth
  • Swelling

Systemic symptoms that may occur along with pus

Pus may accompany symptoms that affect the whole body including:

  • Body aches
  • Coughing up clear, yellow, light brown, or green mucus
  • Difficulty breathing or rapid breathing
  • Discharge from the eye
  • Fainting or change in level of consciousness or lethargy
  • Fatigue
  • Fever and chills
  • Fever not associated with flu symptoms
  • Frequent infections
  • Headache
  • High fever (higher than 101 degrees Fahrenheit)

Symptoms that might indicate a serious condition

In some cases, pus may occur with other symptoms that might indicate a serious condition that should be immediately evaluated in an emergency setting. Seek immediate medical care (call 911) if you, or someone you are with, have pus formation along with other serious symptoms including:

  • Coughing up clear, yellow, light brown, or green mucus
  • Difficulty breathing or rapid breathing
  • Fainting or change in level of consciousness or lethargy
  • Headache
  • High fever (higher than 101 degrees Fahrenheit)
  • Severe pain
  • Severe swelling

What causes pus?

Pus is caused by the breakdown of neutrophils, which are inflammatory cells produced by the body to fight infection. Typically, pus forms during the course of a bacterial infection. Although neutrophils initially engulf and kill bacteria, they themselves are eventually broken down and become a major constituent of pus. All types of bacteria that cause disease are capable of producing infections that lead to pus.

Typical causes of pus

Pus may be caused by bacterial infections or other common conditions including:

What are the potential complications of pus?

Pus is generally a harmless symptom that does not produce long-term complications. However, in some circumstances, pus formation may indicate a serious bacterial infection. Contact your health care provider if you have pus formation along with other symptoms, such as a fever, severe pain, or difficulty breathing. Potential serious complications of pus-producing infections include:

  • Encephalitis (inflammation and swelling of the brain due to a viral infection or other causes)
  • Meningitis (infection or inflammation of the sac around the brain and spinal cord)
  • Myocarditis (infection of the middle layer of the heart wall)
  • Osteomyelitis (bone infection)
  • Sepsis (life-threatening bacterial blood infection)
  • Spondylitis (infection or inflammation of the spinal joints)
  • Spread of infection
  • Tissue damage or destruction
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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2018 Dec 21
  1. Staphylococcal infections. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/000863.htm
  2. Bacterial infections.Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/bacterialinfections.html
  3. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis 2005; 41:1373.
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