When a person has black mucus, they may have inhaled potentially harmful pollutants. Coughing up black mucus may also be due to an underlying infection or condition.

Mucus serves an important purpose in the nasal passages and other cavities throughout the body. It helps protect against infection and harm from foreign objects. Mucus also helps lubricate these passages and cavities.

During an illness, mucus often builds up in the nasal passages and a person can usually blow it out or wipe it away.

Phlegm, which the lungs produce, is very similar to mucus and may also indicate a health issue. A person will often cough up phlegm when viruses, bacteria, or unwanted — possibly cancerous — cells are present in the lungs.

Clear or light-colored mucus often does not indicate a serious health problem, but when a person has black mucus or phlegm, they should see a doctor as soon as possible.

Though black phlegm is not always a cause for concern, it could be a sign of lung cancer or exposure to a pollutant. Figuring out the cause will help the doctor recommend the best course of treatment.

Keep reading for more information about what can cause black mucus or phlegm and ways to treat it.

Pollutants, infections, and lung cancer may cause black mucus or phlegm. Below, we discuss these and other more common causes.


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Air pollution can cause black or dark mucus.

Air pollutants, including particles of dirt or industrial chemicals, can cause dark mucus and phlegm.

People who live in or visit areas with high air pollution may experience black or dark mucus and phlegm.

Sometimes, coal miners develop a condition called pneumoconiosis after exposure to coal dust and other air pollutants in the mines. Other occupational hazards include exposure to silica and asbestos.

In general, once a person leaves an area of heavy pollution, their mucus and phlegm return to a more regular color.

Smoking or secondhand smoke

When a person breathes in smoke, pollutants and other small particles in the smoke get trapped in the mucus and phlegm. This can cause these substances to turn a much darker color. Smoke can also cause the phlegm in the lungs to thicken.

In addition, smoke can damage the hair-like cilia, which help clear the lungs of phlegm. As a result, a person will cough up more dark-colored phlegm.

Smoke from fires

A person exposed to a large fire, such as a house or workplace fire, often breathes in soot and ash.

As in people who smoke or breathe in pollutants, the particles from a fire can turn the mucus and phlegm black. This is one reason that firefighters wear specialized masks and air tanks while fighting a blaze.


Tuberculosis (TB) is a highly contagious bacterial infection that causes a person’s phlegm to turn dark. Other symptoms include chest pain, a persistent cough, and coughing up blood. People with weakened immune systems are especially susceptible to TB.


Pneumonia is a potentially deadly disease that attacks the lungs’ air sacs, causing the lungs to fill with fluid.

In addition to black mucus and phlegm, pneumonia can cause chest pain, shortness of breath, fever, and coughing. Viruses, bacteria, and other infections can cause pneumonia.

Fungal infections in the lungs

A person with a weakened immune system has an increased risk of developing a fungal infection that settles in their lungs, as with TB. People who live in hot environments are also more likely to develop fungal infections in the lungs.

This type of infection can cause bleeding in the airways, and this blood makes the mucus and phlegm appear dark or black.

Lung cancer

According to the American Lung Association, about 541,000 people living in the United States currently have or have had lung cancer.

Lung cancer can cause a range of chest-related symptoms, including dark phlegm. If a person coughs up blood and has dark or black mucus and phlegm, they should see a doctor as soon as possible.

Other causes

The following health issues can also cause black mucus and phlegm:

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A doctor can offer advice on how to quit smoking.

Treatment options for black mucus and phlegm vary, depending on what is causing the discoloration.

To treat an underlying infection, a doctor will need to figure out the cause. They may recommend antifungal or antiviral medications or antibiotics. Sometimes, a doctor prescribes steroids to help reduce inflammation.

People who have darkened mucus due to smoking should stop smoking. In addition to clearing up the mucus, quitting smoking provides many health benefits.

People with lung cancer require treatment, which may include surgery, radiation, chemotherapy, or targeted treatments. A person should discuss their care plan with their healthcare provider.

Anyone exposed to pollutants on a regular basis should take precautionary steps. Wearing a mask or breathing apparatus can help prevent exposure.

Sometimes, no treatment is necessary. For example, a person exposed to pollutants — such as dust, chemicals, or smoke — for a short period will notice that their mucus returns to a regular color once exposure to the pollutants stops.

Dark or black mucus sometimes returns to a regular color quickly. This may happen when temporary exposure to a pollutant, such as smoke, ends.

When other factors are responsible for the change in color, a person should consult a doctor as soon as possible.

See a doctor if any of the symptoms below accompany black mucus:

  • a persistent cough
  • a fever
  • chest pain
  • shortness of breath
  • coughing up blood
  • blood mixed with the black mucus or phlegm

Black mucus is often a warning that something is wrong. If anyone is in doubt, they should schedule an appointment with their healthcare provider as soon as possible.

When a person receives the right treatment, mucus and phlegm often return to a regular color.