A cough lasting beyond 8 weeks (adults) is chronic, and in non-smokers with a normal chest X-ray, three causes explain most cases: upper-airway drip from nose and sinuses, cough-variant asthma, and acid reflux — none obvious, all treatable, often coexisting. The famous fourth: ACE-inhibitor blood-pressure drugs (lisinopril, ramipril) cause a dry cough in up to 1 in 5 users, sometimes starting months in, resolving weeks after a supervised switch. Post-infectious cough bridges 3–8 weeks and self-resolves. Red flags — coughing blood, weight loss, breathlessness, smoking history with a changed cough, fever, night sweats — mean imaging now rather than trials of treatment.
When a cough becomes "chronic"
Coughs live on a timeline: acute (<3 weeks — overwhelmingly viral), subacute (3–8 weeks — mostly the post-infectious tail, where inflamed airways stay trigger-happy after the germ has gone and time is the treatment), and chronic (>8 weeks adult, >4 pediatric), where the puzzle changes character. The reflex itself is protective machinery — sensors in airway walls firing up the vagus to a brainstem cough center — and chronic cough is that circuit stuck sensitized, usually by one of a short list of irritants dripping, squeezing or splashing onto it.
The famous three (plus one)
In non-smoking adults with a clean chest film and no ACE inhibitor, studies attribute the large majority of chronic cough to three conditions, alone or stacked:
1. Upper-airway cough syndrome (post-nasal drip) — rhinitis or sinusitis dripping onto the cough sensors: throat-clearing, a trickle sensation, worse lying down and on waking, often with congestion history. Treatment is the nose's: antihistamines or nasal steroids, saline rinses, allergen work — with the cough fading over weeks as the drip dries.
2. Cough-variant asthma (and eosinophilic bronchitis) — the FAQ's wheeze-free asthma: nocturnal, exercise- and cold-triggered, steroid-responsive.
3. Reflux (GERD/LPR) — with or without heartburn, per the FAQ's silent routes: post-meal and positional pattern, hoarseness and throat-clearing company, managed with acid suppression plus the unglamorous levers (earlier dinners, weight where relevant, head-of-bed elevation).
Plus the medication: ACE inhibitors — the "-pril" blood-pressure class — produce a dry, tickly cough in 5–20% of users via bradykinin accumulation, beginning anywhere from first dose to a year in, and resolving within days-to-weeks of a prescriber-supervised switch (usually to an ARB, which doesn't do it). It is the single highest-yield medication question in the cough clinic — and never a reason to stop a blood-pressure drug unsupervised.
The rest of the cast: smoking's chronic bronchitis (a daily productive cough is early COPD talking — spirometry, not acceptance), pertussis's months-long paroxysms even in vaccinated adults, and the smaller-print causes evaluation exists to catch — COPD, bronchiectasis, interstitial disease, heart failure's nocturnal cough, and the malignancy the red-flag list screens for. When the whole tree comes up empty, refractory chronic cough — a hypersensitized reflex in its own right — is now a recognized diagnosis with specific treatments (speech-therapy cough-control programs, low-dose neuromodulators), which is worth knowing before year three of lozenges.
Red flags — imaging now, not trials of treatment
Coughing blood; unintended weight loss or drenching night sweats; new or changed cough in a smoker or ex-smoker; breathlessness at rest or progressive; chest pain; hoarseness past 3 weeks; recurrent pneumonia; swallowing trouble; fever persisting; or a cough in anyone immune-suppressed. Any of these earns a prompt chest X-ray and review — the step the whole decision tree stands on.
What evaluation looks like
History (timeline, triggers, position, meals, smoking, the medication list with its "-prils"), examination, chest X-ray for any chronic cough, spirometry — then, commonly, sequential treatment trials of the top three, each given honest weeks, singly or together, which is both therapy and diagnosis. Bring a fortnight's pattern notes; they compress the sequence. Cough syrups' honest footnote: OTC suppressants and expectorants perform near placebo in trials — honey genuinely beats them for short-term night cough (never under age one) — and the money saved belongs on the causes above. The "lung cleanse" aisle sold against this symptom gets its grading elsewhere in this hub; a cough that has earned eight weeks has earned a diagnosis, not a detox.
Frequently asked questions
How can reflux cause cough without any heartburn?
Two routes need no burning: micro-aspiration of acid mist irritating the airway, and a vagal reflex from esophagus to cough center that fires on acid exposure alone — "silent reflux" causes a large share of unexplained cough, classically worse after meals, lying down, talking or laughing, often with throat-clearing and hoarseness. It's diagnosed as much by treatment response (acid suppression plus meal-timing changes for 8–12 weeks) as by testing.
I quit smoking and my cough got worse — is that normal?
Briefly, yes and reassuringly: the cilia paralyzed by smoke regrow within weeks and begin sweeping out accumulated mucus — a productive clean-up cough peaking in the first month and fading over two to three. A quitter's cough that persists past that, worsens, or turns bloody exits the reassurance lane and gets imaged, because ex-smokers keep elevated lung-cancer risk for years.
What is cough-variant asthma?
Asthma whose only symptom is cough — no wheeze, no obvious breathlessness — typically dry, worse at night, after exercise, in cold air or around triggers. Standard spirometry can be normal; challenge testing or a monitored inhaled-steroid trial makes the diagnosis, and response is usually gratifying. It, plus its cousin non-asthmatic eosinophilic bronchitis, explains a big slice of the mystery-cough clinic.
When does a child's cough need urgency?
Same-day: breathing hard or fast, ribs sucking in, blueness, drooling with distress (never examine a suspected epiglottitis throat), a coughing-then-whooping or vomiting pattern (pertussis), or a story of sudden choking (inhaled object — classically a one-sided cough). Booked: any cough past 4 weeks in a child, which uses a shorter chronic threshold than adults.
References
- MedlinePlus. Cough (2023). https://medlineplus.gov/cough.html
- National Heart, Lung, and Blood Institute. High Blood Pressure (2024). https://www.nhlbi.nih.gov/health/high-blood-pressure
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