Sputum is produced when a person’s lungs are diseased or damaged. Sputum is not saliva but the thick mucus – sometimes called phlegm – which is coughed up from the lungs.

The body produces mucus to keep the thin, delicate tissues of the respiratory tract moist so that small particles of foreign matter that may pose a threat can be trapped and forced out.

Sometimes, such as when there is an infection in the lungs, an excess of mucus is produced. The body attempts to get rid of this excess by coughing it up as sputum.

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Sputum is a type of mucus that may be expelled when coughing.

There are many different reasons for the body to produce excess sputum. Below is a list of some of these causes, along with how the sputum may appear.


In smokers, mucus builds up in the lungs, causing a “smoker’s cough.” The sputum produced may be green, yellow, or bloody.


People with asthma have airways that are sensitive to allergens, environmental pollution, and respiratory infections. This sensitivity can lead to the airways becoming inflamed, as well as an increase in mucus production.

Cystic fibrosis

Cystic fibrosis is an inherited disease caused by a defective gene. It leads to smaller airways becoming blocked by thick mucus, which causes breathing difficulties.

The thick mucus in cystic fibrosis becomes an ideal environment for bacteria to grow. Many people with cystic fibrosis develop chronic bacterial lung infections.

Respiratory tract infections (RTI)

Sputum that is a different color from saliva may be a sign of a lower RTI. With bacterial RTIs, sputum may also have a thick consistency and an unpleasant odor.

As a general rule, sputum is dark green in the early stages of an infection and gradually lightens as the infection improves. It is the presence of an enzyme called myeloperoxidase that gives the sputum its green color, during an infection.

Some infections may cause sputum to be yellow, gray, or rusty colored.

Common RTIs

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The flu is a common type of RTI, which may cause sputum.


Flu, or influenza, may result in green phlegm. The main symptoms are:

Other common symptoms include general aches and pains, a chesty cough, and cold-like symptoms, such as a blocked or runny nose, sneezing, and a sore throat.

People should rest at home, drink plenty of water, and keep warm. Over-the-counter painkillers will help when someone has the flu, and most people will start to feel better within a week.

If started within 2 days of becoming ill, antiviral drugs such as oseltamivir can lessen the time someone is sick by 1-2 days. Taking antiviral drugs later in the infection can also be beneficial, particularly if someone is very ill or has a high risk of developing complications.


Bronchitis is an infection of the lung’s main airways, the bronchi, which become inflamed and produce extra mucus. People with this condition may cough up yellow-grey or greenish sputum.

Bronchitis is a lung condition that can be acute or chronic.

Acute bronchitis lasts about 3 weeks. Chronic bronchitis is defined as a daily cough that produces sputum and lasts for at least 3 months and occurs for two consecutive years. It is a symptom of other lung conditions, including emphysema and chronic obstructive pulmonary disease (COPD).

Most cases of acute bronchitis can be treated at home with non-steroidal anti-inflammatory drugs (NSAIDs) and by drinking plenty of fluids.



Other common symptoms include:

  • difficulty breathing
  • rapid heartbeat
  • fever
  • feeling generally unwell
  • sweating and shivering
  • loss of appetite

If someone thinks that they have pneumonia, they should see a doctor.

Tuberculosis (TB)

If someone has TB, they may cough up green or bloody phlegm. They will also experience symptoms that can include:

  • weight loss
  • night sweats
  • fever
  • tiredness
  • loss of appetite
  • swelling in the neck

TB is a serious condition but can be treated with a 6-month course of antibiotics.

Although TB is a bacterial infection that mainly affects the lungs, it can impact on the upper body, glands, bones, and nervous system, as well.

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Sputum may be an indication of an RTI, which in some cases will require medical attention.

Anyone who suspects they have TB should seek medical attention and get treatment.

If someone thinks that they may have pneumonia, they should also speak to a doctor. The condition can be difficult to diagnose as it shares symptoms with other common RTIs. Mild pneumonia can be treated at home with antibiotics, rest, and plenty of fluids.

Most other RTIs will resolve by themselves in time. Doctors recommend taking over-the-counter painkillers, drinking plenty of fluids, and resting.

However, there will be times when it is best to seek medical attention. These occasions include when someone has a severe cough that lasts for more than 3 weeks.

If someone has a temperature of over 100.4°F for more than 3 days, this may be a sign of pneumonia, so it is important to see a doctor.

If a person coughs up mucus flecked with blood, is breathing rapidly, develops chest pains, or becomes drowsy or confused, they should go to the doctor.

The same is true for anyone who has an underlying heart or lung condition or has experienced repeated episodes of bronchitis

If someone does visit a doctor, they might be asked to undergo a sputum culture test. This test is used to diagnose bacterial pneumonia or bronchitis. It can also be used to monitor how treatment for a particular condition is working.

The sputum culture test is usually done with a gram stain, which identifies the bacteria that are causing the infection. If the gram stain is unable to detect the bacteria causing the infection, specialized tests may also be run. These include an AFB smear and culture to find tuberculosis and non-tuberculous mycobacteria infections, a fungal culture, or a Legionella culture.

A sputum sample will usually be collected first thing in the morning. Depending on the infection in question, up to three more samples may be taken on the following days.

When being sent for a sputum test, people can be asked to brush their teeth, rinse their mouth out with water, and avoid food for 1-2 hours beforehand.

To produce a sample from the lungs, a person is usually asked to cough deeply. If someone cannot cough up any sputum, they may be asked to inhale a sterile saline or glycerine solution to loosen up the phlegm in the lungs. Steam inhalation can also be used at times.

As well as a sputum culture test, a doctor may ask for someone to have a complete blood count to look for any other signs of illness.