A natural reﬂex reaction to irritation of the AIR PASSAGES and LUNGS. Air is drawn into the air passages with the GLOTTIS wide open. The inhaled air is blown out against the closed glottis, which, as the pressure builds up, suddenly opens, expelling the air – at an estimated speed of 960 kilometres (600 miles) an hour. This explosive exhalation expels harmful substances from the respiratory tract. Causes of coughing include infection – for example, BRONCHITIS or PNEUMONIA; inﬂammation of the respiratory tract associated with ASTHMA; and exposure to irritant agents such as chemical fumes or smoke (see also CROUP).
The explosive nature of coughing results in a spray of droplets into the surrounding air and, if these are infective, hastens the spread of colds (see COLD, COMMON) and INFLUENZA. Coughing is, however, a useful reaction, helping the body to rid itself of excess phlegm (mucus) and other irritants. The physical eﬀort of persistent coughing, however, can itself increase irritation of the air passages and cause distress to the patient. Severe and protracted coughing may, rarely, fracture a rib or cause PNEUMOTHORAX. Coughs can be classiﬁed as productive – when phlegm is present – and dry, when little or no mucus is produced.
Most coughs are the result of common-cold infections but a persistent cough with yellow or green sputum is indicative of infection, usually bronchitis, and suﬀerers should seek medical advice as medication and postural drainage (see PHYSIOTHERAPY) may be needed. PLEURISY, pneumonia and lung CANCER are all likely to cause persistent coughing, sometimes associated with chest pain, so it is clearly important for people with a persistent cough, usually accompanied by malaise or PYREXIA, to seek medical advice.
Treatment Treatment of coughs requires treatment of the underlying cause. In the case of colds, symptomatic treatment with simple remedies such as inhalation of steam is usually as eﬀective as any medicines, though ANALGESICS or ANTIPYRETICS may be helpful if pain or a raised temperature are among the symptoms. Many over-the-counter preparations are available and can help people cope with the symptoms. Preparations may contain an analgesic, antipyretic, decongestant or antihistamine in varying combinations. Cough medicines are generally regarded by doctors as ineﬀective unless used in doses so large they are likely to cause sedation as they act on the part of the brain that controls the cough reﬂex.
Cough suppressants may contain CODEINE, DEXTROMETHORPHAN, PHOLCODINE and sedating ANTIHISTAMINE DRUGS. Expectorant preparations usually contain subemetic doses of substances such as ammonium chloride, IPECACUANHA, and SQUILL (none of which have proven worth), while demulcent preparations contain soothing, harmless agents such as syrup or glycerol.
A list of systemic cough and decongestant preparations on sale to the public, together with their key ingredients, appears in the British National Formulary.