Cough — Causes, Types & When to See a Doctor — Causes, Diagnosis & When to See a Doctor | MyMedicPlus

Cough is a powerful protective airway reflex that clears the respiratory tract of irritants, inhaled foreign particles, excessive mucus, and pathogens. It is one of the most frequent reasons people consult a doctor — accounting for up to 30 million outpatient visits annually — and is caused by stimulation of cough receptors located throughout the upper and lower respiratory tract, including the larynx, trachea, bronchi, and lung parenchyma. Cough is classified by duration: acute cough lasts fewer than 3 weeks, subacute 3–8 weeks, and chronic more than 8 weeks. Acute cough is almost always caused by a viral upper respiratory infection. Chronic cough — defined as persisting beyond 8 weeks — is more diagnostically complex and has a defined differential diagnosis that a physician must systematically evaluate. Understanding the duration, character (dry versus productive), timing, and associated symptoms of a cough is essential to accurate diagnosis. While the majority of coughs are self-limiting and benign, coughing up blood (haemoptysis) and cough associated with unexplained weight loss, night sweats, or voice change are red flag features requiring urgent evaluation for potentially serious conditions including pulmonary tuberculosis, lung cancer, or pulmonary embolism.

Acute cough is overwhelmingly caused by viral upper respiratory tract infections including the common cold (rhinovirus, adenovirus), influenza A and B, COVID-19, and respiratory syncytial virus (RSV — particularly dangerous in infants and older adults). Pertussis (whooping cough) caused by Bordetella pertussis is a bacterial cause of severe acute and subacute cough characterised by paroxysmal coughing followed by an inspiratory whoop, and remains common in under-vaccinated populations. Subacute cough often represents post-infectious cough persisting after a viral illness due to airway hypersensitivity. Chronic cough has a defined triad of most common causes: upper airway cough syndrome (UACS, formerly post-nasal drip syndrome) from allergic or non-allergic rhinitis and chronic sinusitis is the single most common cause; cough-variant asthma presents as a persistent dry cough triggered by cold air, exercise, or irritants without wheeze; gastro-oesophageal reflux disease (GERD) causes cough via vagal reflex activation and microaspiration. ACE inhibitor medications (lisinopril, ramipril, perindopril) cause a persistent dry tickling cough in up to 15% of users. Additional causes of chronic cough include eosinophilic bronchitis, bronchiectasis, COPD, lung cancer, pulmonary fibrosis, heart failure (cardiac cough is worse when lying flat), tuberculosis, and environmental irritant exposure (occupational lung disease).

Seek emergency care immediately for coughing up blood (haemoptysis) — any amount of blood-stained sputum requires evaluation, as causes range from benign bronchitis to lung cancer and pulmonary embolism. Call emergency services for cough accompanied by severe difficulty breathing, oxygen desaturation (bluish lips or fingertips), or stridor (high-pitched inspiratory noise indicating upper airway obstruction). Seek urgent same-day care for cough with high fever above 38.5°C, pleuritic chest pain, and coloured sputum indicating possible pneumonia — particularly if associated with confusion or breathlessness in elderly or immunocompromised patients. A cough with a characteristic barking sound (croup in children) or an inspiratory whoop following paroxysms of coughing (pertussis) in unvaccinated individuals or after close contact with a confirmed case requires prompt assessment. In adults, a chronic cough persisting more than 8 weeks with unexplained weight loss, night sweats, or persistent hoarseness (dysphonia) must be evaluated promptly for possible lung cancer, lymphoma, or laryngeal pathology. A cough that progressively worsens in a smoker with a history of heavy tobacco use always warrants chest imaging to exclude lung cancer.

Clinical history is the most important diagnostic tool. The physician establishes the duration (acute versus chronic), character (dry and tickling, wet and productive, paroxysmal), timing (worse at night — asthma and GERD; worse on lying down — GERD and heart failure; occupational patterns), sputum characteristics (colour, consistency, quantity, presence of blood), exacerbating and relieving factors, associated symptoms (wheeze, breathlessness, heartburn, post-nasal drip, voice change), smoking history, medication use (particularly ACE inhibitors), and travel or exposure history. Chest X-ray is the essential first-line investigation for persistent or unexplained cough, identifying pneumonia, lung masses, pleural effusion, hilar lymphadenopathy, and heart failure. Spirometry with bronchodilator reversibility testing quantifies airway obstruction and confirms asthma or COPD — a methacholine challenge test induces bronchospasm to detect airway hyperresponsiveness in suspected cough-variant asthma when spirometry is normal. Peak flow diary over 4 weeks demonstrates diurnal variability characteristic of asthma. Sputum culture and sensitivity identifies bacteria in productive cough. Fractional exhaled nitric oxide (FeNO) measures eosinophilic airway inflammation. High-resolution CT chest is the definitive investigation for suspected interstitial lung disease, bronchiectasis, or lung cancer. 24-hour oesophageal pH impedance monitoring or upper GI endoscopy investigates GERD as a cough cause. Fibreoptic bronchoscopy directly visualises endobronchial lesions and obtains biopsies and lavage samples.

Viral acute cough resolves spontaneously within 2–3 weeks without specific treatment in most cases. Honey (1–2 teaspoons before bed) has consistent evidence for reducing cough frequency in adults and children over 1 year; it is as effective as over-the-counter cough suppressants. Adequate hydration thins secretions. Menthol and steam inhalation provide symptomatic relief. Post-nasal drip from allergic rhinitis responds to intranasal corticosteroid sprays (fluticasone, mometasone), antihistamines, and saline nasal irrigation (neti pot). Cough-variant asthma is treated with short-acting beta-2 agonist inhalers (salbutamol) for acute relief and inhaled corticosteroids (beclomethasone, fluticasone) as maintenance therapy — cough typically resolves within 4–8 weeks of starting inhaled steroids. GERD-related cough is treated with twice-daily proton pump inhibitors for at least 8 weeks, combined with dietary modification (avoiding fatty foods, alcohol, coffee, and chocolate), elevation of the bed head, and weight loss. ACE inhibitor cough resolves within 1–4 weeks of switching to an angiotensin receptor blocker (ARB). Pertussis is treated with macrolide antibiotics (azithromycin or clarithromycin) to reduce contagion, though they have limited effect on cough duration. Bacterial pneumonia requires targeted antibiotic therapy based on severity and likely organism (amoxicillin first-line for community-acquired pneumonia). Chronic refractory cough (cough hypersensitivity syndrome) may respond to gabapentin, pregabalin, or speech and language therapy focusing on laryngeal control.

Vaccination is the most powerful preventive intervention for many cough-causing infections. Annual influenza vaccination reduces influenza-related cough and its complications, particularly in older adults and those with chronic respiratory disease. COVID-19 vaccination reduces severe respiratory disease. Pertussis (whooping cough) vaccination with Tdap booster is recommended for adults every 10 years, and especially for pregnant women (to protect newborns) and those in contact with infants. Pneumococcal vaccination prevents bacterial pneumonia in high-risk adults. Smoking cessation is the single most impactful prevention for chronic cough and COPD — smokers are 3–4 times more likely to develop a chronic productive cough (chronic bronchitis) and 25 times more likely to develop lung cancer than non-smokers; benefits of cessation begin within weeks. Avoid second-hand smoke exposure, occupational respiratory irritants (asbestos, silica, dust, fumes), and air pollution where possible. Proactive treatment of underlying asthma, GERD, and allergic rhinitis prevents these conditions from causing or perpetuating chronic cough. Frequent handwashing during respiratory virus season reduces transmission of cold and influenza viruses. Stay adequately hydrated to maintain effective mucociliary clearance.

Call emergency services immediately for coughing up significant amounts of blood, cough with severe breathing difficulty (unable to complete a sentence, bluish discolouration), or stridor indicating upper airway obstruction. Seek same-day emergency assessment for cough with high fever above 38.5°C, confusion, and breathing difficulty — possible pneumonia, particularly in those over 65, immunocompromised, or with chronic lung or heart disease. See a doctor within a few days for cough producing coloured (green, yellow, rust-coloured) sputum lasting more than 5–7 days, cough following a bout of choking or aspiration in an older adult or child, or cough in an infant under 3 months old. Schedule a GP appointment within 2 weeks for any cough lasting more than 3 weeks that has not improved, or cough in a smoker with any change in cough character, voice change, or systemic symptoms. Chronic cough lasting beyond 8 weeks always warrants a systematic medical investigation including chest X-ray as a minimum. Children with a cough having a paroxysmal character or a whooping quality, particularly after close contact with a sick person, need prompt assessment for pertussis regardless of vaccination status.