Productive cough (coughing up phlegm): causes, red flags and when to see a GP

A productive cough is one that brings up mucus, also called phlegm or sputum. It differs from a dry, tickly cough, and its causes lean towards the lower airways and lungs rather than the throat and nose. NICE CKS describes cough as a reflex to airway irritation and notes that acute cough is most commonly caused by a viral upper respiratory infection, with acute bronchitis and pneumonia among the other causes.

The colour of mucus is a weak guide to the cause. The NHS lists coughing up green or yellow mucus as a symptom of chest infection and of pneumonia, but the NHS also stresses that a viral chest infection does not need antibiotics, so colour alone does not decide treatment.

The NHS cough page says most coughs are caused by a cold or flu, with smoking, heartburn, allergies, infections such as bronchitis or COVID-19 and mucus dripping from the back of the nose as other causes. A productive cough narrows the list to the following.

For urgent advice the NHS cough page lists a cough that is very bad or quickly gets worse, feeling very unwell, chest pain, a swollen painful gland at the side of the neck, difficulty breathing and coughing up blood, and recommends an urgent GP appointment or NHS 111. The NHS bronchitis page adds being over 65, pregnant, having a long-term heart, lung or kidney condition or diabetes, a weakened immune system, feeling too unwell for daily activities and being short of breath.

The NHS pneumonia page puts more serious signs at the A&E or 999 level: struggling to breathe, pale, blue or blotchy skin, lips or tongue, coughing up blood and sudden confusion. The NHS bronchiectasis page says coughing up more than a few spots or streaks of blood could be serious bleeding in the lungs and needs 999 or A&E. A cough lasting over 3 weeks with weight loss, night sweats or loss of appetite should lead to a GP review, as the TB and cough pages indicate.

• Blood in the phlegm, even a few streaks, which warrants an urgent assessment; more than a few spots means 999.

• Struggling to breathe, being unable to speak in full sentences, or blue or grey lips.

• New confusion, especially in an older person.

• Cough longer than 3 weeks, particularly with weight loss, night sweats or loss of appetite.

• Chest pain that comes and goes or is triggered by breathing or coughing.

• Underlying heart, lung, kidney or immune conditions, or age over 65.

The NHS says a GP may listen to the chest with a stethoscope, take a sample of mucus, and order an X-ray, allergy test or lung function test. Questions usually concern how long the cough has lasted, the colour and amount of phlegm, any blood, breathlessness, fever, smoking, occupational exposure, medicines such as ACE inhibitors that CKS lists as a cause of chronic cough, and recent contact with TB.

CKS describes pulse oximetry when someone is acutely unwell, peak flow if asthma is possible, a C-reactive protein test if pneumonia is suspected and spirometry and chest X-ray for a chronic cough of uncertain cause. The CRB-65 score, which counts confusion, fast breathing, low blood pressure and age 65 or more, helps decide whether an adult with pneumonia can be treated at home.

The NHS chest infection page suggests resting, drinking lots of water to loosen mucus, raising the head on extra pillows, using painkillers for temperature and aches, and a hot lemon and honey drink (not honey for under 12 months). It says not to smoke, not to give aspirin to under 16s, and not to let children breathe steam from a bowl because of scalding risk.

A pharmacist can suggest cough medicine to loosen mucus, though the NHS says some cough medicines are unsuitable for children, and decongestants or cough medicines containing codeine will not stop the cough. If you have a high temperature, the NHS asks you to stay home and avoid others; covering coughs and sneezes, disposing of tissues and handwashing reduce spread.

A GP is the right contact for a cough that persists beyond 3 weeks, comes with weight loss, or occurs in someone with a weakened immune system. The NHS says people over 65, pregnant, or with a long-term health condition should seek advice earlier. A respiratory specialist is involved when a cough does not respond to a trial of treatment or the cause is unclear, as CKS notes.

People who keep getting chest infections can ask about the annual flu vaccine and the pneumococcal vaccine, which the NHS says helps prevent pneumonia, and about support to stop smoking.