Persistent cough: what to do when it lasts for weeks

A cough that lasts more than three weeks is no longer just a cold, and if it goes on for more than eight weeks it is considered a chronic cough. In most cases, a persistent cough has common, treatable causes: the nose, asthma, reflux or a medicine. To find yours, what helps most is describing clearly what it is like, when it appears and what comes with it.

How long a normal cough lasts and when it counts as persistent

In adults, three timeframes are used:

• Acute cough, lasting less than three weeks. It nearly always comes with a cold or a respiratory infection and goes away by itself.
• Subacute cough, lasting three to eight weeks. This is very typical after an infection: the airways remain irritated and the cough takes time to settle, although it gradually eases.
• Chronic cough, lasting more than eight weeks. It can no longer be explained by the latest cold and deserves a methodical investigation.

These timeframes are a guide, but they don't mean you have to wait. If the cough isn't improving, is getting worse or comes with other symptoms, there is no need to reach eight weeks before seeing a doctor.

Why won't my cough go away? The most common causes

In a person who doesn't smoke and has a normal chest X-ray, a chronic cough is usually due to one or more of these causes, which often occur together:

• Nose and sinuses. Rhinitis or sinusitis makes mucus run down the back of the throat (known as post-nasal drip). You notice a scratchy throat, a need to clear it and more coughing when you lie down.
• Asthma. It doesn't always cause wheezing or breathlessness: in some people, coughing is the only symptom, and it gets worse at night, in the cold, with exercise or with strong smells. We explain this on the asthma page.
• Gastro-oesophageal reflux. Contents coming up from the stomach can irritate the throat and cause coughing, sometimes without heartburn. It tends to get worse after eating, when lying down or after talking a lot.
• Medicines. Some blood pressure medicines, known as ACE inhibitors (many end in ‘-pril’), cause a dry, irritating cough that can appear weeks or months after you start taking them.
• Smoking. ‘Smoker's cough’ is not harmless: it can be the first warning of COPD, a disease that progresses for years before causing breathlessness.

Less often, a persistent cough is due to bronchiectasis (permanently widened airways), diseases of the lung tissue, tuberculosis, heart failure or a lung tumour. These are the causes the investigation must rule out when there are warning signs or risk factors, which is why it's best not to let months go by without seeing a doctor.

Warning signs: when not to wait

Book an appointment without delay if your cough comes with:

• Blood when you cough, even if only streaks.
• Shortness of breath that is getting worse or that appears with efforts you used to manage without any problem.
• Unintentional weight loss, night sweats or severe tiredness.
• A fever that won't go down, or thick, foul-smelling phlegm.
• Chest pain or hoarseness that won't go away.
• A cough that changes in character in a smoker or ex-smoker.
• Recent contact with someone who has tuberculosis.

Call 112 if you are finding it very hard to breathe, if your lips turn bluish, if you cough up a large amount of blood or if your face or throat swell up.

What information helps at an appointment for a persistent cough

The medical history is half the diagnosis. Before your appointment, it's worth noting down:

• How long you have had the cough and whether it started with a cold or flu.
• When it appears: when you lie down, in the early hours, when you get up, after eating, when talking, with exertion or when breathing cold air.
• What it is like: dry or with phlegm, and what colour.
• What comes with it: wheezing, chest tightness, throat clearing, a blocked nose, heartburn or hoarseness.
• All your medication, with names and start dates, including your blood pressure medicine.
• Smoking and vaping, current or past, and exposure at work or at home: dust, fumes, chemicals, damp, birds.
• What you have tried (cough syrups, inhalers, antibiotics) and whether you noticed any change.

With that information the specialist can form a specific suspicion and order only the tests that confirm or rule it out, rather than a battery of tests with no clear question.

How a cough that lasts for weeks is investigated

The investigation begins with a conversation and an examination, paying attention to the nose and throat and listening to the lungs. From there, the most common tests are:

• Chest X-ray, the first imaging step to rule out lesions in the lung. You can see what it involves on the X-ray page.
• Spirometry with a bronchodilator test, which measures how air leaves the lungs before and after a medicine that opens the airways, and helps to identify asthma or COPD.
• Depending on what is suspected, blood tests, allergy testing or other tests.

When the most likely cause is the nose, asthma or reflux, a treatment for that cause can be tried for a few weeks to see whether the cough responds: that response is also part of the diagnosis. If nothing fits, the specialist considers more specific tests.

What you can do in the meantime

• If you smoke, stopping is what protects your airways most. At the stop smoking clinic they can help you do it.
• Don't stop your blood pressure medicine on your own, even if you suspect it's giving you a cough: talk to your doctor, who will consider changing it for another one.
• Avoid smoke and any irritants you notice set it off.
• Cough syrups can bring relief for a few days, but they don't treat the cause: if the cough continues, the solution lies in finding it.

If your cough has already lasted more than three weeks or you have any of the warning signs, the respiratory medicine clinic is the place to organise the investigation and leave with a plan.