What is Sputum?

What is Sputum or Phlegm and What Causes it to be Increased?

photo of sputum on a tissue
What is sputum?. Wikimedia Commons/User Zhangmoon618

What exactly is sputum and is it the same thing as phlegm, mucus, or saliva? What does it mean if your sputum is different colors, such as clear, white, yellow, green, or red, and what conditions can result in increased sputum production?

Sputum: Definition and Description

Sputum is a mucousy substance that is secreted into the airways (bronchi and bronchioles) of the respiratory tract. 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 is made up of a combination of cells and other matter that is present in the airways.

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.

Source of Sputum

Sputum or phlegm is coughed up from the lower airways in the respiratory tract—the bronchi, bronchioles, and trachea—rather than glands in the mouth and throat.

Colors of Sputum and What it Means

Sputum can be many colors and consistency, and these can help define 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
  • Brown sputum: Brown sputum due to the presence of tar, is sometimes found in people who smoke. 
  • 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.
  • Bloody sputum: Bloody sputum, even just a trace of blood tinged sputum, should always be evaluated. Coughing up blood can be serious, and is the first sign of lung cancer in 7 percent of people. Even 1 to 2 teaspoons of coughed up blood is considered a medical emergency.

Contents of Sputum

Sputum is made up from secretions from cells lining the respiratory tract, dead cells, foreign matter than is breathed into the lungs, and white blood cells and other immune cells. In infections, bacteria may also be present in sputum. Blood may also be present in the sputum with lung cancer, trauma to the respiratory tract, damage to the airways, and pulmonary edema.

Conditions That Increase Sputum Production

Some conditions that result in increased production of sputum include:

  • Bronchiectasis: Bronchiectasis is a form of chronic obstructive pulmonary disease (COPD) often caused by chronic respiratory infections in childhood.
  • Pulmonary Edema
  • Overproduction of sputum can be caused by smoking and exposure to air pollution

Tests to Evaluate Sputum

Sputum may be analyzed in the lab to determine its contents and more. Tests may include:

  • Sputum culture: A sputum culture is done by placing a sample of a sputum in a growing media (agar dish) and looking for the presence of growth. This can be done to determine the particular type of bacteria causing pneumonia. Once the bacterial strain is determined, the lab can then do further tests to figure out which antibiotic is most effective against that bacteria.
  • Sputum for tuberculosis: A sputum sample may be obtained to look for tuberculosis.
  • Sputum cytology: In ​sputum cytology as a sample of sputum is evaluated under the microscope. This can be done to look for signs of tuberculosis or signs of cancer cells. At one time it was thought that sputum cytology could a screen for lung cancer, but it is not an effective screening tool. If cancer cells are found, however, it can be diagnostic of lung cancer. Further tests will then need to be done to find out the location of the cancer.

Decreasing Sputum Production

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. In that case 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.

Bottom Line on Sputum

Sputum is a substance produced by the respiratory tract which contains a combination of cells, foreign matter, and white blood cells. The color, consistency, and amount of sputum can be important in diagnosing a number of different medical conditions. Visualization of sputum may also aid in the diagnosis of conditions such as tuberculosis and even lung cancer. Though an increased amount of sputum can be very annoying, it is often the body's attempt to rid itself of material (such as tar and other foreign matter) that could otherwise lodge in and damage the airways.

Also Known As: phlegm


U.S. National Library of Medicine. Routine sputum culture. Updated 07/05/17. https://medlineplus.gov/ency/article/003723.htm