Coughing at night can result from several different mechanisms, and the timing of the cough provides useful but non-specific diagnostic information. Common causes include asthma, gastro-oesophageal reflux, post-nasal drainage or upper-airway disease, respiratory infections, COPD and environmental irritants. Lying down can alter airway secretions, reflux mechanics and nasal drainage, which may explain why a person who coughs relatively little during the day becomes much more symptomatic at night. Night-time cough should therefore be interpreted alongside symptoms such as wheezing, heartburn, nasal congestion, sputum, breathlessness and the presence of known respiratory disease.
Asthma is a particularly important cause of nocturnal coughing. Asthmatic airway inflammation and bronchial hyper-responsiveness can vary over the 24-hour cycle, and some people experience increased airway narrowing during the night. Cough may occur with wheezing, chest tightness or breathlessness, although cough can occasionally be the dominant symptom. Bedroom allergens such as house-dust-mite particles, animal dander or mould can also contribute in susceptible individuals. Cold bedroom air, smoke and other inhaled irritants can aggravate airway symptoms. A recurrent cough that repeatedly wakes a person or is accompanied by wheeze warrants assessment for asthma and other respiratory conditions.
Gastro-oesophageal reflux is another common explanation for night-time cough. Lying down removes the gravitational assistance that helps keep gastric contents in the stomach, and eating shortly before bed can increase the amount of material present in the stomach during the night. Refluxed material can irritate the oesophagus and may stimulate cough through oesophageal-airway reflex pathways or, in some circumstances, direct irritation of upper-airway tissues. Night cough associated with a sour taste, regurgitation, heartburn or symptoms after late meals makes reflux more plausible. Nevertheless, not every nocturnal cough is caused by reflux, and persistent cough should be assessed in the context of other possible causes.
Upper-airway mucus and nasal disease can also become more noticeable when lying down. Allergic rhinitis, sinus disease and other causes of nasal inflammation can increase mucus production or cause drainage towards the throat. This can stimulate cough receptors and produce repeated throat clearing, particularly during prolonged periods lying horizontally. Nasal blockage may also encourage mouth breathing, which can dry and irritate the throat. Symptoms such as sneezing, itchy eyes, nasal congestion, facial pressure or a sensation of mucus at the back of the throat can help point towards an upper-airway contribution.
Respiratory infections can cause cough that persists into the night even after other symptoms begin to improve. Viral infections can leave the airways temporarily hypersensitive and irritated, so a cough may continue after fever or nasal symptoms have resolved. Bronchitis and pneumonia can also produce persistent cough, often with sputum, fever, chest discomfort or breathlessness. A cough that is steadily improving after an acute infection is different from one that persists without improvement, repeatedly returns or becomes progressively worse. The latter pattern requires consideration of asthma, chronic airway disease, reflux, medication effects and less common causes.
COPD and other chronic airway diseases can also produce nocturnal cough. Chronic mucus production can accumulate when physical activity and coughing are reduced during sleep, while airway narrowing can contribute to symptoms. Smoking and exposure to second-hand smoke, dust, fumes and air pollution may maintain airway irritation. In people with established COPD, a change from the usual cough pattern, particularly increased sputum, changed sputum colour, worsening breathlessness or fever, can indicate an exacerbation or infection and may require medical assessment.
Environmental factors in the bedroom can maintain or trigger nocturnal coughing. Tobacco smoke, fragrances, aerosols, dust, mould and other airborne irritants can provoke airway inflammation or sensitivity. Bedroom temperature and humidity can also affect symptoms in susceptible individuals, although there is no universal ideal environment for every respiratory condition. House-dust mites and animal allergens may be especially relevant when symptoms occur predominantly during sleep in a person with allergic asthma or rhinitis. Identifying a consistent relationship between exposure and symptoms can help clinicians determine whether an environmental trigger is involved.
Persistent night cough should not be dismissed simply because it occurs only during sleep. Clinical assessment is particularly important when the cough lasts for weeks, repeatedly disrupts sleep, is accompanied by breathlessness, wheezing, chest pain, fever, unexplained weight loss or coughing up blood, or occurs in someone with significant smoking exposure. Coughing up blood with difficulty breathing, a very fast heartbeat or chest or upper-back pain can require emergency assessment because pulmonary embolism is one possible cause. The appropriate evaluation may include chest examination, spirometry, chest imaging, reflux assessment or other tests depending on the associated symptoms.
