Cough lasting more than three weeks: causes, red flags and when to get it checked

The cough reflex is triggered by irritation in the airways, throat or even the oesophagus. When it lasts beyond three weeks, the cause is often an irritated, over-sensitive airway after infection or a continuing trigger such as acid, drip or an allergy. A smaller group of coughs signal lung disease that needs a scan.

• Post-viral cough after a cold, flu or COVID-19, gradually improving over several weeks.

• Asthma or cough-variant asthma, with night cough, wheeze or tightness and a response to inhalers.

• Upper airway cough syndrome: postnasal drip from allergy or sinus disease with throat clearing.

• Gastro-oesophageal reflux, sometimes with no heartburn.

• ACE inhibitor medicines for blood pressure, causing a dry tickly cough that settles after stopping.

• Smoking, COPD and chronic bronchitis, with morning phlegm.

• Whooping cough, bronchiectasis and, in some regions, tuberculosis.

• Lung cancer, interstitial lung disease and heart failure, which are less common but important.

Coughing up blood, unexplained weight loss, night sweats, breathlessness, chest pain, a hoarse voice, swollen glands, a smoking history, being over 40, previous cancer, or contact with tuberculosis raise concern.

• Call 999: coughing up a large amount of blood, severe breathlessness or chest pain.

• Urgent GP referral (suspected cancer pathway, chest X-ray within two weeks): a cough lasting over three weeks with weight loss, blood, or in smokers over 40.

• GP within days: cough with fever, breathlessness or worsening wheeze.

• Routine GP: a dry tickly cough after a cold lasting three to eight weeks, otherwise well.

Doctors ask how long, whether it is dry or productive, timing, triggers, wheeze, reflux, nose symptoms, medicines (especially ACE inhibitors), smoking, occupation, weight change and sweats. They check oxygen saturation, listen to the chest, look at the throat and nose and examine for clubbing and lumps.

• Chest X-ray: the first test for a cough lasting beyond three weeks with risk factors.

• Spirometry and peak flow: for asthma and COPD.

• Sputum tests: if infection is suspected.

• CT chest and bronchoscopy: for abnormal X-rays or persistent unexplained cough.

• Trial of treatment for asthma, reflux or rhinitis, where appropriate.

Stay hydrated, use honey and lemon in warm water for adults, avoid smoke, and raise your head at night. Stop an ACE inhibitor only on medical advice; your GP can switch it. Saline nasal rinses help postnasal drip. Cough medicines have limited benefit.

The NHS route is a GP, chest X-ray and respiratory clinic. Private respiratory consultations, same-day chest X-ray and CT can be arranged directly.