1. Overview Coughing removes secretions from the respiratory tract and expels inhaled pathogenic and foreign substances, and is an important defense mechanism. However, frequent and violent coughing, which affects the patient’s breathing, sleep and daily work, is one of the most common symptoms. The stimuli that cause the cough reflex are inflammation, bruising, physicochemical factors or tumors. Coughs are usually classified into 3 categories according to their duration: acute cough, subacute cough and chronic cough. Acute cough lasts <3 weeks, subacute cough 3 to 8 weeks, and chronic cough ≥8 weeks. A chronic cough with a negative chest radiograph is called chronic cough of unknown origin, or chronic cough for short. 2. Present medical history (1) Acute onset and duration of illness Acute cough is mostly seen in colds, acute pharyngitis, acute bronchitis, pneumonia, pneumothorax and pleurisy; chronic cough starts slowly and is mostly seen in chronic pharyngitis, chronic bronchitis, tuberculosis, lung cancer, bronchiectasis, interstitial lung disease, etc. (2) Nature and timbre of cough Short light cough is seen in dry pleurisy, pleural trauma or after chest surgery; barking cough is mostly seen in laryngeal spasm; low hoarse cough is mostly seen in vocal fold swelling and vocal fold paralysis; metallic sounding cough is mostly seen in bronchopulmonary cancer, lymph node enlargement or esophageal cancer compressing the bronchus; weak cough is seen in general failure, respiratory muscle weakness and during anesthesia for thoracic and abdominal surgery; whooping cough can Whooping cough can have paroxysmal spasmodic cough with bird-like inspiratory sounds. (3) Time of cough, triggering or aggravating factors, and postural effects Morning cough is seen in chronic bronchitis and bronchiectasis; nocturnal cough is seen in left heart failure and asthma; cough during feeding is seen in esophageal-tracheal fistula; cough caused by postural changes is seen in bronchiectasis, abscess chest with bronchopleural fistula, mediastinal tumor, and massive pleural effusion. (4) Sputum volume Dry cough is commonly seen in pharyngitis, laryngitis, early tuberculosis, pneumoconiosis, lung cancer and pleurisy, etc.; coughing small amount of sputum is seen in early acute bronchitis, pneumonia, tuberculosis, etc.; coughing more sputum is seen in bronchiectasis, lung abscess, abscess chest with bronchopleural fistula and some alveolar cell carcinoma, etc. (5) Sputum color and nature White mucous sputum is seen in bronchitis; pus sputum is seen in lung abscess, bronchiectasis and abscess chest combined with bronchopleural fistula; rust-colored sputum is seen in lobar pneumonia; brick-red jelly-like sputum suggests Klebsiella pneumoniae pneumonia; chocolate-like sputum is seen in amoebic lung abscess; yellow-green sputum is seen in Pseudomonas aeruginosa infection in the lung; white sticky and difficult to cough out by drawing into filaments suggests fungal infection; pink foamy sputum suggests left heart failure; dark red blood sputum is mostly due to mitral stenosis or pulmonary infarction; fresh blood sputum is seen in lung cancer, tuberculosis and pulmonary infarction; rotten peach-like or jam-like sputum is seen in pulmonary schistosomiasis; gray or black sputum is seen in pneumoconiosis; pus-flavored sputum is seen in anaerobic bacterial infection. (6) Accompanying symptoms Large amount of hemoptysis is seen in bronchiectasis, lung abscess, tuberculosis cavity, etc.; small amount of hemoptysis or hematochezia is seen in endobronchial tuberculosis, bronchial calculus, lung cancer, etc. Chest pain is seen in pleurisy, pleural tumor or pneumonia and lung cancer involving the pleura, etc. Dyspnea is seen in chronic bronchitis, emphysema, diffuse interstitial lung fibrosis, etc. High fever is seen in infectious pneumonia, lung abscess, etc., and low fever is seen in tuberculosis, etc. 3. Relevant medical history (1) Age and sex. For young or young onset, consider tuberculosis, bronchiectasis and asthma; for elderly, consider chronic bronchitis and lung cancer; for young women, consider connective tissue disease causing lung lesions. (2) Past history. Focus on whether there is a history of measles, whooping cough, bronchopneumonia (persistent), chronic bronchitis, bronchiectasis, tuberculosis; whether there is a history of heart disease; whether there is a history of connective tissue disease, uremia and malignancy; whether there is a history of allergic diseases. (3) Living and working environment. Smoking and passive smoking are closely related to chronic bronchitis and lung cancer; for those with long-term dust exposure, pneumoconiosis should be considered; for those exposed to toxic and hazardous gases and oil fumes, chronic cough may be related to the work environment; for those who develop cough when first entering the plateau or mountaineering, attention should be paid to altitude sickness. (4) Medication and treatment measures. If cough occurs after application of angiotensin-converting enzyme inhibitors to lower blood pressure and is relieved after stopping the drug, cough is a drug reaction; application of cytotoxic drugs (bleomycin, mitomycin, cyclophosphamide, etc.) and non-cytotoxic drugs (furantadine, lorazepam, etc.) can cause drug-related lung damage; for those with chest radiation therapy, radiation pneumonia should be considered.