What Is Sputum?

Learn what increases it and what colors mean

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Sputum, or phlegm, is a type of mucus secreted by cells in the lower airways (bronchi and bronchioles) of the respiratory tract. It differs from saliva, which is produced higher up in the mouth.

Sputum may contain dead cells, foreign debris inhaled into the lung, bacteria, and white blood cells that protect the airway from infection. The quantity, texture, and color of sputum can help to diagnose lung cancer and other medical conditions that affect sputum production.

This article explains what sputum is and looks like. It discusses sputum culture tests and procedures, such as sputum induction, that are used to assess sputum when identifying and treating respiratory illnesses.

Sputum Types

Sputum is secreted into the lower airways (bronchi and bronchioles) of the respiratory tract. It is produced by cells called goblet cells that line the airway, and it contains immune cells to fight off bacteria. It works with small structures in the airway called cilia to trap and remove foreign substances.

Sputum is not the same as saliva, a substance secreted in the mouth to help with digestion. The terms sputum and phlegm are used interchangeably.

Sputum or phlegm is coughed up from the bronchi, bronchioles, and trachea rather than glands in the mouth and throat. It may include foreign matter from air pollution or smoking cigarettes, as well as bacteria from an infection, or blood due to cancer, airway damage, and pulmonary edema.

The term mucus may sometimes be used instead of sputum, but sputum refers to that mucus specifically secreted in the respiratory tract, whereas mucus may also be produced in the gastrointestinal tract, urological tract, and genital tract.

Tests to Evaluate Sputum

Sputum may be analyzed in the lab to determine its contents in order to evaluate infections or look for cancer. Tests may include:

  • Sputum culture: A sputum culture is done in a laboratory to identify the presence and type of cells in a sputum sample that may cause disease. If a specific bacteria is found, the lab can then do further tests to figure out which antibiotic is most effective against that bacteria (sensitivity testing).
  • Sputum for tuberculosis: A sputum sample may be obtained to look for tuberculosis, though several samples are often needed in order to find one that is diagnostic.
  • Sputum cytology: In sputum cytology, a sample of sputum is evaluated under the microscope. This can be done to look for signs of tuberculosis or signs of cancer cells. However, sputum cytology is not a reliable lung cancer screening tool. If cancer cells are found, however, it can be diagnostic of lung cancer and further tests determine the location of the cancer.

Sputum Induction

Some people may have difficulty coughing up sputum from deep in the lungs. A cytology technique called sputum induction, first developed to diagnose pneumonia in people living with human immunodeficiency virus (HIV), is now used to assess diseases such as asthma, chronic obstructive pulmonary disease (COPD), or idiopathic pulmonary fibrosis. It involves inhaling a mist of Albuterol (salbutamol) mixed with saline to make sputum production easier.

What Sputum Colors Mean

Sputum qualities can include many colors and different consistencies, and these can help to diagnose certain conditions. For example:

  • Clear sputum: Clear sputum is usually normal, although it may be increased in some lung diseases. 
  • White or gray sputum: White or grayish tinged sputum can also be normal, but may be present in increased amounts with some lung diseases or precede other color changes associated with other conditions.
  • Dark yellow/green sputum: A type of white blood cells known as neutrophils have a green color to them. These types of white blood cells are attracted to the scene of bacterial infections, and therefore bacterial infections of the lower respiratory tract, such as pneumonia, may result in the production of green sputum. Yellow-green sputum is common with cystic fibrosis as well.
  • Brown sputum: Brown sputum due to the presence of tar is sometimes found in people who smoke. Sputum may also appear brown or black due to the presence of old blood. Brown sputum is also common with "black lung disease." These diseases, called pneumoconioses, occur from inhaling substances like coal into the lungs.
  • Pink sputum: Pink, especially frothy pink sputum may come from pulmonary edema, a condition in which fluid and small amounts of blood leak from capillaries into the alveoli of the lungs. Pulmonary edema is often a complication of congestive heart failure. Pink or blood-tinged sputum is commonly caused by tuberculosis worldwide.
  • Bloody sputum: Bloody sputum, even just a trace of blood-tinged sputum, should always be evaluated. Coughing up blood (hemoptysis) can be serious, and is the first sign of lung cancer in 7% to 35% of cases.

Coughing up Blood in Sputum

Blood in sputum is always serious and requires immediate medical evaluation. It can be a sign of lung cancer or pulmonary embolism, a condition in which a blood clot breaks off and travels to the lungs. Even a teaspoon of coughed-up blood is considered a medical emergency. Coughing up a fourth of a cup of blood is considered massive hemoptysis and carries a poor prognosis.

Causes of Increased Sputum

Some conditions that result in increased production of sputum include:

  • Chronic bronchitis: Chronic bronchitis results in increased sputum. The criteria for a diagnosis of chronic bronchitis includes a daily cough productive of sputum
  • Bronchiectasis: This is a form of chronic obstructive pulmonary disease (COPD). It is often caused by chronic respiratory infections in childhood, with about half of cases due to cystic fibrosis.
  • Pulmonary edema
  • Overproduction of sputum can also be caused by smoking and exposure to air pollution.
Possible causes of increase phlegm production

Verywell / Cindy Chung

Decreasing Sputum

There are a number of ways in which to decrease sputum production, but the most important step is to diagnose and treat the underlying cause.

With air pollution and smoking, the underlying cause is the body's attempt to rid itself of foreign matter, and an overproduction of sputum is a normal response. Tobacco smoke causes paralysis in cilia. They can't move sputum up to the mouth due to the lower mobility, so it accumulates in the airways. Removing the source is the best approach.

Medications that may help decrease sputum include aerosol treatments and expectorants. Treatments such as postural drainage may be effective in some situations.


Sputum is a mix of cells, foreign matter, and white blood cells produced in the respiratory tract. An increased amount of sputum is often the body's attempt to protect and heal damage to the airways. Contact your healthcare provider if you have chronic or concerning symptoms. An accurate diagnosis may lead to earlier treatment and improved outcomes.

Frequently Asked Questions

  • What does green phlegm mean?

    Green phlegm is a possible sign of a bacterial infection.Coughing up discolored phlegm can be worrisome, but the color actually shows that your body is fighting the infection. If your symptoms worsen or don’t improve, you may need antibiotics to clear the infection.

  • How can I get rid of mucus in my throat?

    First treat any underlying conditions, like allergies or a cold. Replace filters in heating and air cooling systems to improve air quality. Drink plenty of water. You can use a humidifier to help clear mucus from your chest and throat. Saline sprays to rinse your nasal passages are another easy way to release sputum.

  • What does sputum from COPD look like?

    The color and look of sputum from COPD can vary from person to person. It may be white and frothy, or it can be mucus-like, cloudy, and greenish, which could indicate you have a bacterial infection. Thicker-than-usual sputum is common with COPD.

  • What causes blood in sputum?

    Common causes for blood found in sputum include: chest infection, bronchiectasis, and even severe nosebleed. Less common causes include pulmonary embolism, lung cancer, and tuberculosis. Even if there are only a few spots of blood in your sputum, reach out to your healthcare provider right away.

12 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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By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."