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To eliminate foreign substances from the airways and lungs. A cough is a noisy expulsion of air through the mouth caused by a sudden contraction of the diaphragm. It defends the breath from the aggression of microbes, flu infections, pollution, dust and smoke, among other agents, and can serve to eliminate excess secretion in the airways. But there are also sensors that trigger coughs from other, unsuspected parts of the body, such as the sinuses (the hollows in the face bone), the esophagus, the stomach and even the heart. A transient cough does not indicate a problem. But if it persists, it is possible that it is a symptom of something serious. “In smokers, persistent chronic coughing can be a sign of lung cancer”, says pulmonologist Hélio Romaldine, from the Paulista School of Medicine, Federal University of São Paulo (Unifesp).