What phlegm is
The airways are lined with a thin layer of mucus that traps dust, germs and irritants. Tiny hairs move it up towards the throat, where it is usually swallowed without noticing. When the airways are irritated or infected, they produce more mucus, which becomes thicker and is coughed up as phlegm or sputum.
Mucus from the nose and sinuses can also drip down the back of the throat and be coughed or cleared up; see postnasal drip.
Phlegm color chart
- Clear: normal mucus, allergies, the start of a viral infection or postnasal drip.
- White or grey: congestion, viral infections, smoking, reflux or chronic lung conditions such as COPD.
- Yellow: white blood cells responding to an infection, viral or bacterial.
- Green: a more established inflammatory response; still often viral.
- Brown: old blood, smoking, dust or pollution; sometimes bronchiectasis or a chest infection.
- Black: inhaled smoke, coal dust or pollution; rarely a fungal infection.
- Pink or red: blood from an irritated airway, a nosebleed or, more seriously, the lungs.
Does yellow or green phlegm mean a bacterial infection?
Not necessarily. The yellow-green colour comes from enzymes in white blood cells, which are present in both viral and bacterial infections. Most coughs with yellow or green phlegm are caused by viruses and get better on their own within 2 to 3 weeks.
Antibiotics may be needed when there are signs of a bacterial chest infection or pneumonia, such as high fever, breathlessness, chest pain or feeling very unwell, or in people with chronic lung conditions. A doctor decides based on the whole picture, not the colour alone. See also yellow snot.
Brown and black phlegm
Brown phlegm is common in smokers, especially in the morning, and in people exposed to dust or pollution. It can also contain old blood after a nosebleed or a chest infection. Persistent brown phlegm, particularly in large amounts every day, can be a sign of bronchiectasis or COPD and should be assessed.
Black phlegm usually follows inhaling smoke, for example after a fire, or coal or industrial dust. See black mucus. If there was no exposure, or it persists, see a doctor.
Pink, red or bloody phlegm
- Small streaks of blood can come from a strained throat after coughing hard or from a nosebleed.
- Pink, frothy phlegm with breathlessness can be a sign of fluid in the lungs and needs emergency care.
- Coughing up more than a few streaks of blood needs prompt medical assessment.
- Blood in phlegm with weight loss, night sweats or a long-standing cough should always be checked.
Common causes of excess phlegm
- Colds, flu and other viral infections.
- Chest infections, bronchitis and pneumonia.
- Postnasal drip from rhinitis or sinusitis.
- Smoking and vaping.
- Asthma and COPD.
- Acid reflux, including laryngopharyngeal reflux.
- Bronchiectasis, which causes a daily productive cough.
How to clear phlegm
- Drink plenty of fluids to keep mucus thin.
- Breathe in steam from a hot shower or a bowl of hot water.
- Use saline nasal rinses if the mucus comes from the nose.
- Sleep with your head slightly raised.
- Avoid smoke and other irritants.
- Try controlled coughing or huffing to bring phlegm up.
See how to get rid of phlegm and wet cough.
Phlegm in smokers
Smoking damages the tiny hairs that clear mucus, so smokers often cough up white, grey, yellow or brown phlegm every morning. This is not normal, even if it is common. It can be an early sign of COPD, and stopping smoking is the most effective way to reduce it; the cough often improves within weeks to months after quitting.
When to see a doctor
- Coughing up blood, or pink frothy phlegm.
- Breathlessness, chest pain or wheezing.
- High fever or feeling very unwell.
- A cough with phlegm lasting more than 3 weeks.
- Weight loss, night sweats or a change in a long-standing cough.
- A chronic lung condition with more or darker phlegm than usual.
Key points to remember
- Phlegm colour reflects inflammation, irritants or blood, not the exact cause.
- Yellow and green phlegm are common in viral infections and do not always need antibiotics.
- Brown or black phlegm often follows smoking, dust or smoke exposure.
- Blood, breathlessness or a cough over 3 weeks need medical assessment.
Questions about phlegm color
These answers are general information and do not replace an examination or individual medical advice.
What does yellow phlegm mean?
It usually means your immune system is responding to an infection, most often a virus.
Is green phlegm worse than yellow?
Not necessarily. Both reflect inflammation; how you feel and other symptoms matter more.
What does brown phlegm mean?
It can contain old blood or come from smoking, dust or pollution. Persistent brown phlegm should be checked.
Do I need antibiotics for green phlegm?
Not usually. Most cases are viral. A doctor decides based on fever, breathing and examination.
Why is my phlegm clear and foamy?
Clear phlegm is often linked to allergies, postnasal drip or the start of a cold. Pink frothy phlegm with breathlessness needs urgent care.
How long does phlegm last after a cold?
Phlegm and cough can last 2 to 3 weeks after a cold.
Sources
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.