Yellow sputum: what it can mean

Mucus may turn yellow when immune cells and proteins mix with it during inflammation. This can happen with a viral respiratory illness as well as some bacterial infections. Coughing up phlegm is common in acute bronchitis, while pneumonia can also present with cough, sputum, fever, chest discomfort, or breathlessness. Postnasal drainage from chronic sinusitis may produce coloured mucus that is coughed up, particularly after lying down.

A change in colour is less informative than the whole pattern: how long the cough has lasted, whether symptoms are improving, and whether there is wheeze, pain, or shortness of breath.

Drink fluids if you can, rest, and avoid smoking or vaping because these can irritate the airways. Note when the cough began and whether the amount of phlegm is changing. A clinician can listen to your chest and decide whether an examination or treatment is appropriate; antibiotics are not automatically useful for every cough with yellow mucus.

Seek urgent assessment for trouble breathing, blue or grey lips, confusion, severe chest pain, coughing blood, or a rapidly worsening illness. Arrange medical review for a persistent cough, repeated episodes, fever that is not settling, or sputum with a new unpleasant smell. People with COPD or bronchiectasis should follow their usual action plan and contact their care team when symptoms change.

Ask whether your breathing sounds suggest airway narrowing or a chest infection, whether testing is needed, and which symptoms should prompt faster follow-up. Bring a list of medicines, inhalers, recent illnesses, and any history of lung disease.