The body produces mucus, also known as phlegm or sputum, to protect sensitive tissues in the airways. Changes in the color, thickness, or quantity of phlegm may indicate a health problem.

Mucus consists of mucins and other proteins. The body produces mucus to keep the thin, delicate tissues of sensitive areas — such as the respiratory tract — moist.

Mucus lines and protects sensitive surfaces inside the body, and it helps trap and remove small particles of foreign matter that may pose a threat.

Sometimes, the lungs produce too much mucus. The body attempts to expel this excess by coughing it up as sputum or phlegm.

Here, learn about what changes in phlegm can mean and what to do if they happen.

The different colors of sputum can indicate whether a person has a health problem and what kind of problem they may have. Here are some of the colors that may be present.

ColorReason
clear, white, or grayusually indicates healthy lungs, but a lot of sputum may indicate a lung disease, allergy, or viral infection
dark yellow or greencan indicate a bacterial or viral infection, such as pneumonia, or cystic fibrosis, an inherited condition that involves excess mucus buildup
brownoften occurs in people who smoke and those with black lung disease, a condition resulting from exposure to coal dust
pinkcan indicate pulmonary edema (fluid on the lungs), from a condition such as congestive heart failure
redcan be a sign of an internal injury, lung cancer, or a pulmonary embolism (PE), which is a blood clot on the lung that needs immediate medical attention

There are many reasons why the body produces excess sputum or sputum with an unusual color or texture.

They include:

Smoking

Smoking increases the risk of various diseases, including lung cancer, chronic bronchitis, and chronic obstructive pulmonary disease (COPD).

One reason for excess mucus production may be to protect the lungs from damage due to particles.

However, one older study from 2011 suggested that smoking may suppress a protein known as Bik in the lungs of smokers with chronic bronchitis. Usually, this protein kills unwanted mucus cells. However, it seems that smoking may prevent this by reducing the action of Bik, resulting in excess mucus production.

What to know about smoker’s cough.

Asthma

People with asthma have airways that are sensitive to allergens, such as pollen and air pollution. They also have a higher risk of respiratory infection.

These factors can lead to airway inflammation and cause the airways to produce additional mucus as they try to protect themselves.

Treatment options include identifying and avoiding triggers and using inhalers to manage or prevent attacks.

Cystic fibrosis

A person with cystic fibrosis (CF) has inherited genetic features that cause the body to produce thick mucus. This unusually thick mucus can block the airways and cause breathing difficulties.

The thick mucus in CF becomes an ideal environment for bacteria to grow, increasing the risk of infection.

Doctors often diagnose CF at birth, as it is part of the screening process for newborns. A person with CF will likely receive ongoing follow-up care.

Treatment options include:

  • drugs that help change the protein that causes mucus to thicken
  • mechanical removal of sputum
  • breathing support

The person will also need to take measures to avoid respiratory infections, as they can be life threatening in people with CF.

Respiratory tract infections

Sputum that is a different color from saliva may be a sign of a lower respiratory tract infection (RTI), which affects the lungs. Examples include bacterial or viral pneumonia and bronchitis.

With bacterial RTIs, sputum may also have a thick consistency and an unpleasant odor.

In the early stages of an RTI, sputum may be dark green or yellow. As the infection retreats, the color becomes lighter. It is the presence of an enzyme called myeloperoxidase that gives the sputum its green color during an infection.

Here are some examples of RTIs that may affect sputum.

COVID-19

Some people with COVID-19 have a dry cough, but around 30% have a cough that produces sputum. This can aggravate breathing problems.

One study suggests that those with breathing problems early in the disease may develop more severe symptoms and have a worse outcome than those who first notice a fever, pain, and diarrhea.

Other symptoms of COVID-19 include:

Treatment options include:

  • isolating
  • resting at home
  • using over-the-counter (OTC) pain relief medications

A doctor may prescribe antiviral medications if a person has a high risk of severe infection due to another health condition.

A person needs emergency medical help if they have:

Flu

Flu, or influenza, is a viral infection. A person with the flu may have green or yellow phlegm.

Other symptoms include:

People may treat the flu by:

  • resting at home
  • avoiding other people
  • using OTC pain relievers
  • taking antiviral drugs, if a doctor prescribes them

Vaccines can help prevent the flu.

Bronchitis

Bronchitis is an infection of the lung’s main airways: the bronchi. They become inflamed and produce extra mucus. A person may cough up clear, gray, or greenish phlegm.

Acute bronchitis lasts about 3 weeks and usually goes away without treatment. Treatment includes resting, drinking plenty of fluids, and taking nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief.

Chronic bronchitis lasts at least 3 months and is recurring. It is a symptom of other lung conditions, including emphysema and COPD. Avoiding smoking can help manage it.

If symptoms worsen or do not improve, people should speak with a doctor. The following groups have a greater risk of developing pneumonia:

  • older adults
  • those who smoke
  • people with compromised immune systems or other health conditions

Pneumonia

A person with pneumonia may have a dry cough or a cough that produces thick sputum that is yellow, green, brown, or blood-stained.

This is a viral or bacterial infection that leads to the swelling of lung tissue.

Other common symptoms include:

If someone thinks they have pneumonia, they should seek medical advice. Anyone who is unable to breathe or is coughing up blood should seek emergency help.

Treatment options include resting, drinking plenty of fluids, and taking antibiotics if the infection is bacterial. Some people may need to spend time in the hospital.

Tuberculosis

Tuberculosis (TB) is a bacterial infection. It usually affects the lungs but can occur in other parts of the body, such as the stomach.

A person with TB in the lungs may cough up blood or blood-streaked phlegm.

Other symptoms include:

  • a severe cough lasting 3 weeks or longer
  • chest pain
  • weakness and fatigue
  • low appetite and weight loss
  • fever and chills
  • night sweats

People with TB will need a course of antibiotics lasting several months, but some types of TB are becoming resistant to antibiotics.

A person should consult a doctor if they believe they may have:

  • asthma
  • TB
  • bronchitis
  • pneumonia

It is best to seek medical advice if a person has:

  • a cough that is severe or does not go away
  • traces of blood in their sputum
  • concerns about any symptoms

Anyone with the following symptoms should seek emergency medical help:

  • breathing difficulty
  • chest pain
  • a rapid heart rate
  • coughing up blood
  • confusion
  • a high fever

If a person has signs of COVID-19, they should stay home and avoid contact with other people. However, anyone with an underlying health condition or compromised immune system should seek medical advice.

Those with breathing difficulties need emergency medical care.

How do you stop a runny nose?

A doctor might recommend a sputum culture test for someone with a change in their sputum.

This can help:

  • identify the reason for changes in sputum
  • monitor how treatment for an existing condition is working
  • show whether a condition is worsening

To perform a sputum culture test, a person will need to rinse their mouth with water, breathe deeply, and then cough into a container.

To facilitate the production of sputum, the doctor may:

  • tap on the person’s chest to loosen any sputum
  • ask the person to inhale a salty vapor
  • pass a bronchoscope — a thin, lighted tube with a small brush at the end — through the mouth and into the airways to collect a sample

The person may need to avoid eating or drinking for 2 hours before the test.

The doctor may also recommend further tests to identify bacteria that may be causing the problem.

Here are some answers to questions people often ask about phlegm and sputum.

Is phlegm the same as sputum?

Sputum is another word for phlegm. Both terms refer to mucus that people cough up from the lungs. Scientists may also call it “airway surface liquid.” Mucus is present in other parts of the body as well.

What causes phlegm?

The body produces mucus to protect the lungs and help remove debris. Sometimes, the body may produce extra mucus, such as in the case of an infection.

People with cystic fibrosis have a genetic feature that causes their bodies to produce extra mucus. Blood in mucus may result from damage to airway tissue.

What do the different colors mean?

Mucus is usually clear, gray, or white. Green or yellow mucus may be a sign of an infection. Brown mucus can affect people who smoke and those with black lung disease, which results from exposure to coal dust. Mucus that contains blood may be pink or red.

Mucus is an essential fluid that helps protect sensitive tissues inside the body. It consists of proteins and other substances. Mucus in the airways, known as phlegm or sputum, helps remove dust and debris and keep the lungs clear.

Sometimes, problems arise that can change the thickness, amount, or color of mucus. Anyone with concerns about changes in their phlegm or sputum should seek medical advice.

If a person is coughing up blood or has difficulty breathing, they need emergency medical attention.