When should you see a doctor about coughing up phlegm?

Phlegm is mucus brought up from the airways. It may increase during acute bronchitis or pneumonia, while bronchiectasis and COPD can cause recurrent or ongoing sputum. Chronic sinusitis can drain mucus into the throat and trigger coughing. Colour alone cannot confirm a bacterial infection, so the whole pattern and your health history matter.

Drink fluids if you can, avoid smoking and dusty air, and rest while unwell. Note the amount, colour, thickness, smell, duration, fever, wheeze, and ability to breathe or exercise. Do not share antibiotics or use leftover medicine. A clinician may listen to your chest, review inhalers, and decide whether tests or antibiotic treatment are appropriate.

Seek emergency help for severe breathlessness, blue lips, confusion, fainting, chest pain, or coughing up more than a small streak of blood. Arrange prompt review for persistent fever, worsening cough, repeated chest infections, foul-smelling sputum, new wheezing, or a noticeable decline in usual activity. People with COPD or other lung disease should follow their agreed action plan.

Ask whether the phlegm pattern suggests airway infection, sinus drainage, COPD, or another cause; whether a sample or chest test is needed; and when antibiotic treatment would help. Ask how to recognise a flare-up and which symptoms should trigger same-day care.