Cough is usually divided into 3 categories according to the duration of the disease: acute cough <3 weeks, subacute cough 3 weeks - 8 weeks, and chronic cough ≥8 weeks. Chronic cough is defined as a person with cough as the only symptom or the main symptom for more than 8 weeks, no significant abnormalities on chest X-ray, and exclusion of common respiratory diseases such as chronic bronchitis, bronchial asthma, and tuberculosis. Chronic cough is a common clinical symptom with a very complex etiology that is more difficult to diagnose. The common causes include upper airway cough syndrome, cough variant asthma, eosinophilic bronchitis, gastroesophageal reflux disease, followed by angiotensin-converting enzyme inhibitor-induced cough, tracheal hyperreactivity after viral infection, bronchiectasis, endobronchial tuberculosis, lung cancer, adult pertussis, cardiac cough, nodular disease, etc. Very rarely, it is also caused by thyroid disease. With so many causes, how can they be identified clinically? ①It is important to pay attention to the examination of the throat and nose. When a patient has a short cough that is unpleasant to cough and worsens when lying on the back, it often suggests postnasal drip. A "barking cough" is often a bacterial epiglottitis, and laryngeal disorders present as a "growling cough". In patients with hoarseness and cough, think about the possibility of coughing due to vocal cord nodules. (2) Severe cough at night suggests heart failure and asthma. ③Cough associated with diet, especially with heartburn and acid reflux, suggests gastroesophageal reflux disease. ④Cough with hemoptysis is often due to branched expansion, tuberculosis and tumors. ⑤ Paroxysmal spasmodic coughing for 10 to 2O times followed by deep inspiration and high-pitched roaring is characteristic of whooping cough. (6) Cough caused by certain drugs is a side effect, especially cough induced by ACEI drugs is common in clinical practice. (7) Although smokers sometimes have a cough, they still need to be alert to the possibility of lung cancer when the nature or form of the cough changes. (8) In some patients, cough is induced by mental stress and anxiety, and various tests are negative.