A Cough That Will Not Go Away: Working Through the Causes
A cough lasting more than eight weeks is a chronic cough. At that point it is no longer the tail end of an infection, and reaching for another bottle of syrup is unlikely to help, because almost all cough mixtures have weak evidence and none treat the underlying cause.
The usual suspects
In adults who do not smoke, have a normal chest X-ray and are not taking an ACE inhibitor, the great majority of chronic cough comes down to three causes, often in combination.
Upper airway cough syndrome, previously called post-nasal drip. Mucus from the nose and sinuses irritating the throat. Clues: frequent throat clearing, a sensation of something dripping at the back of the throat, nasal congestion, worse in the morning and when lying down.
Asthma and cough-variant asthma. Asthma can present with cough alone, without wheeze or breathlessness. Clues: worse at night or in the early morning, triggered by cold air, exercise, dust or laughter, seasonal variation, personal or family history of allergy. Spirometry may be normal, so a trial of inhaled steroid or specific testing is sometimes needed.
Reflux. Acid or non-acid reflux irritating the larynx and airway. Clues: worse after meals or lying down, hoarseness, throat clearing, a lump-in-throat sensation. Notably, many people with reflux-related cough have no heartburn at all, which is why it is missed.
ACE inhibitor cough. A dry, tickly cough affecting a notable minority of people on drugs ending in -pril. It can start weeks or even months after beginning the drug, which breaks the mental link. It resolves after stopping, though resolution can take up to four weeks. If you are on an ACE inhibitor and have a persistent dry cough, this is the first thing to address, and an ARB is a straightforward substitute.
Post-infectious cough. Following a viral infection or whooping cough, a cough can persist for weeks to months as the airways remain hypersensitive. It resolves with time.
Smoking and chronic bronchitis.
Red flags requiring prompt investigation
- Coughing blood
- Unintentional weight loss
- Fever, night sweats
- Progressive breathlessness
- Hoarseness lasting more than three weeks
- Chest pain
- A smoking history, current or past
- Difficulty swallowing
- A new cough in someone over 40 who smokes or has smoked
- Recurrent chest infections in the same area
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In regions where tuberculosis is common, a cough lasting more than two to three weeks with fever, night sweats or weight loss should prompt TB evaluation, including sputum testing, rather than another course of ordinary antibiotics.
What investigation usually involves
A careful history, which does most of the work; examination; chest X-ray; spirometry with reversibility testing; and depending on findings, allergy assessment, a trial of treatment for the suspected cause, sputum testing, CT scanning, or referral for bronchoscopy or specialist cough clinic.
Trials of treatment are legitimate diagnostics here. A four to eight week trial of nasal steroid, or inhaled steroid, or acid suppression, aimed at the most likely cause, is a standard approach.
Chronic cough hypersensitivity
Some people have a cough that persists after every treatable cause has been addressed. This is now understood as a hypersensitivity of the neural cough reflex, similar in concept to chronic pain. Triggers become trivial: talking, laughing, perfume, cold air, a change in temperature.
It is a recognised condition, not a failure of will. Treatments include speech and language therapy focused on cough suppression techniques, which has genuine evidence, and neuromodulator medicines such as low-dose gabapentin or morphine under specialist supervision. Newer drugs targeting the cough reflex specifically are emerging.
About cough medicines
The honest position: over-the-counter cough preparations have weak evidence of benefit in adults and are not recommended for young children, in whom some ingredients carry real risk.
Honey has modest evidence in children over one year and is safer than most alternatives. Never give honey to an infant under one because of botulism risk.
Antibiotics do nothing for a cough caused by a virus, allergy, asthma or reflux, which covers the large majority of chronic cough.
Practical measures while investigating
- Stop smoking, and avoid second-hand smoke
- Review whether you take an ACE inhibitor
- Treat nasal symptoms properly, with a steroid nasal spray used correctly for several weeks rather than a decongestant for a few days
- Raise the head of the bed if reflux is suspected, and leave three hours between eating and lying down
- Humidify dry indoor air
- Reduce exposure to cooking smoke, incense and indoor pollution
- Stay hydrated, which thins secretions
Nasal spray technique, since it is almost always wrong
Aim the nozzle outward, towards the ear on the same side, not up towards the bridge of the nose. Use the opposite hand to the nostril. Do not sniff hard after spraying; it pulls the medicine straight down the throat. Expect two to four weeks of regular use before judging the effect.
The short version
Chronic cough is usually nasal, asthmatic, reflux-related or drug-induced, and each has a different treatment. Cough syrup addresses none of them. Check whether you are on an ACE inhibitor, treat the most likely cause properly for a full four to eight weeks, and treat blood, weight loss, fever or a smoking history as reasons to be investigated rather than treated empirically.