If you or someone you care about is coughing up black mucus (also called phlegm or sputum), it’s natural to feel worried. Black is an uncommon color for mucus, and seeing it can raise concerns about what might be happening in your body — or in your loved one’s.

While black mucus can sometimes be a sign of lung cancer, there are other possible causes of coughing up dark-colored mucus. Here's what you should know and how to decide on your next steps.

Black Phlegm and Lung Cancer

Coughing up black phlegm can sometimes be a sign of lung cancer. If you haven’t been diagnosed with lung cancer, reach out to your doctor. Also, be aware of other common symptoms of lung cancer, such as:

• Chest pain
• A persistent cough that doesn’t go away
• Coughing up blood
• Shortness of breath
• Fatigue, even when well-rested
• Unexplained weight loss

If you notice any of these signs, inform your doctor when discussing your black phlegm.

Black phlegm may occur if a lung cancer tumor restricts blood circulation to part of your lungs. Without blood flow, that tissue will die. You may then cough up that tissue, and it can appear as black phlegm.

Black Phlegm and Metastatic Melanoma

Another type of cancer, called melanoma, can sometimes spread (metastasize) to the lungs. When this happens, it may cause black mucus. The lungs are rarely the first place melanoma appears. It usually starts somewhere else on the body and then spreads.

Even if melanoma spreads to the lungs, it’s still considered melanoma, not lung cancer. This means it’s diagnosed and treated as melanoma.

If you currently have melanoma, or have had it in the past, be sure to mention it when talking with your doctor about coughing up black mucus.

What Else Causes Black Phlegm?

There are several other potential causes for black phlegm.

Smoking

Smoking is one of the main causes of black phlegm. Inhaling the chemicals in cigarettes can cause the buildup of a substance called sticky tar in the lungs. This dark substance shows up on the chest X-rays of people who smoke. If you cough any of this up, it can make your phlegm black.

Smoking marijuana can also harm the lungs. While research is still ongoing, marijuana smoke contains many of the same harmful chemicals found in cigarette smoke. As a result, it may also contribute to black mucus.

Exposure to Some Chemicals

Inhaling certain substances can also cause black phlegm. This most often affects people who work in environments with regular exposure to certain chemicals or airborne particles, though any kind of smoke or fine dust can damage the lungs.

If you’re regularly breathing in coal dust — or other dark particles like dirt, ash, or industrial dust — you may be more likely to cough up dark-colored mucus. In some areas, air pollution can also expose you to these harmful substances.

To help protect your lung health, consider using safety equipment like masks or respirators, especially if you're in a high-risk environment.

Fungal Infection

A type of fungal infection called Exophiala dermatitidis can also cause black mucus. This type of fungal infection is rare and occurs most frequently in people with compromised immune systems.

If your immune system is compromised from chemotherapy or other factors, inform your healthcare provider when discussing your black phlegm.

Other Conditions

Various other medical conditions or lung diseases can cause your lungs to produce black phlegm. These include:

• Some types of pneumonia
• Chronic obstructive pulmonary disease (COPD)
• Cystic fibrosis
• Tuberculosis
• Bronchiectasis (a condition in which the airways are wider than normal, leading to a buildup of mucus)

You can be diagnosed with any of these conditions in addition to lung cancer. You can also experience them entirely separately from that. You and your doctor will need to work together to make sure you find the source of your black phlegm.

Talk to a Doctor if You’re Concerned

If you or someone you care about has been diagnosed with lung cancer, new or changing symptoms may appear over time. Keeping your healthcare team informed about symptoms — such as coughing up black mucus — helps ensure that your treatment plan stays on track and that symptoms affecting your quality of life are managed as well as possible.

Let your doctor know if your coughing gets worse or if you're producing more mucus than usual. It's also important to report any changes in the color of your mucus. Sharing this information can help your care team detect and treat possible complications early, before they become more serious. If you have trouble breathing or feel chest tightness, contact your doctor right away or go to the emergency room.

If you haven’t been diagnosed with lung cancer and you notice black mucus, talk to your doctor as soon as possible. They can help figure out what might be causing it — lung cancer may be one possibility. Your care team will guide you through any necessary testing and help treat the root cause. Your doctor can also recommend ways to manage related symptoms, like coughing.

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On MyLungCancerTeam, people share their experiences with lung cancer, get advice, and find support from others who understand.

Have you or a loved one ever noticed black phlegm and wondered what it could mean? Let others know in the comments below.