Why mucus can turn black
Mucus is produced continuously by the lining of the nose, sinuses and airways. It traps dust, microbes and pollutants, and tiny hairs (cilia) move it towards the throat, where it is swallowed or coughed up. Normal mucus is clear or white. Its colour changes with what it contains: yellow or green with white blood cells during infection, red or brown with blood, and grey or black when it contains carbon particles, dirt, dried blood or, rarely, fungal material.
Black specks or streaks in otherwise normal mucus are much more common than mucus that is entirely black. The colour, how long it lasts and the symptoms that come with it are the key clues. For other colours, see yellow snot.
Common causes of black mucus
- Smoking and vaping: tobacco and cannabis smoke deposit tar and soot in the airways, so smokers often cough up grey or dark phlegm, especially in the morning.
- Air pollution: heavy traffic, city smog and indoor pollution from cooking on open flames.
- Fires and wood smoke: bonfires, wildfires, wood stoves and fireplaces.
- Occupational dust: coal, construction, mining, metalwork, sanding and some factory work. Repeated exposure needs proper respiratory protection.
- Dried blood: dark brown or black flecks from a dry, cracked nasal lining, picking, a recent nosebleed or nasal surgery; see blood when blowing your nose.
- Food and drink: dark foods, coffee or liquorice can stain mucus at the back of the throat temporarily.
Less common but important causes
- Fungal sinusitis: fungi such as Aspergillus can form a fungal ball in one sinus or cause allergic fungal sinusitis, with thick, dark brown to black mucus, blocked nose and facial pressure, often on one side. It is treated by an ENT specialist, usually with endoscopic sinus surgery.
- Invasive fungal infection: rare, but serious, in people with poorly controlled diabetes, cancer treatment, transplants or other causes of weakened immunity. Black crusts in the nose, facial swelling, pain or numbness need emergency care.
- Lung conditions: black phlegm can occur in severe lung disease from coal dust (pneumoconiosis), in chronic obstructive pulmonary disease (COPD) in smokers, and in some lung infections.
- Bleeding from the lungs: old blood can make phlegm dark. Coughing up blood always needs medical assessment.
Clues to the cause
- Black specks for a day or two after smoke or dust exposure, feeling well: inhaled particles; it should clear on its own.
- Dark brown flecks in a dry nose, especially in winter or with nasal sprays: dried blood.
- Black mucus mainly from one side of the nose with blockage and facial pain: possible fungal sinusitis; see an ENT specialist.
- Black phlegm with chronic cough and breathlessness, in a smoker or dusty job: needs a lung assessment.
- Black crusts, facial swelling or numbness with diabetes or low immunity: emergency.
What you can do
- Avoid the source: stop smoking or vaping, avoid smoky environments and use proper masks for dusty work.
- Rinse the nose with saline to clear particles and moisten the lining; see neti pot sinus rinse.
- Drink plenty of fluids to keep mucus thin.
- Use a humidifier in dry, heated rooms, and avoid picking the nose.
- Apply a thin layer of petroleum jelly or saline gel inside the nostrils if the lining is dry and cracked.
- For thick mucus in the throat, see how to get rid of phlegm.
How an ENT specialist investigates it
An ENT specialist examines the inside of the nose with a thin camera (nasal endoscopy) to look for dry areas, crusts, polyps or fungal material and to see where the mucus comes from. Samples can be sent for fungal culture. A CT scan of the sinuses shows fungal balls and the extent of sinus disease. If the mucus comes from the chest, a doctor may arrange a chest X-ray, sputum tests and breathing tests, and refer to a lung specialist.
When to see a doctor
- Black mucus lasting more than a few days with no obvious exposure.
- Coughing up blood or blood-stained phlegm.
- Fever, facial pain or swelling, or swelling around the eye.
- Black crusts in the nose, numbness of the face or vision changes: emergency care, especially with diabetes or weak immunity.
- Breathlessness, wheezing or chest pain.
- Unexplained weight loss or night sweats.
- Symptoms on one side of the nose lasting more than three weeks.
Key points to remember
- Black mucus is usually from inhaled smoke, pollution or dust, or from dried blood.
- It should clear within a day or two once the exposure stops.
- Persistent black mucus with sinus symptoms can be fungal sinusitis and needs an ENT assessment.
- People with diabetes or weak immunity and black nasal crusts need urgent care.
Questions about black mucus
These answers are general information and do not replace an examination or individual medical advice.
Why is my mucus black?
Most often because of inhaled smoke, pollution or dust, or old blood from a dry nose. Fungal infection is a less common cause.
What do black specks in mucus mean?
Usually trapped particles such as soot or dust. They should clear within a day or two after the exposure ends.
Is black mucus a sign of fungal infection?
Sometimes. Dark, thick mucus with blocked nose and facial pressure, especially on one side, can be fungal sinusitis.
Is black phlegm from smoking normal?
It is common in smokers, but it shows lung irritation. A persistent cough in a smoker should be checked.
Can a nosebleed cause black mucus?
Yes. Old, dried blood looks dark brown or black and can appear for a few days after a nosebleed.
When is black mucus an emergency?
When it comes with black nasal crusts, facial swelling or numbness, vision changes or breathing difficulty, especially with diabetes or weak immunity.
Sources
- NHS · Sinusitis (sinus infection)
- NHS · Aspergillosis
- NHS · Coughing up blood
- NHS · Chronic obstructive pulmonary disease (COPD)
This guide is for general information and does not replace medical advice. How a problem is diagnosed and treated depends on your examination and medical history. If you think you have an emergency, contact your local emergency services.