As a respiratory physician, I know that one of the most confusing respiratory symptoms for patients, and one that is often not clearly diagnosed and treated appropriately, is chronic or long-lasting cough. Therefore, it is necessary to introduce patients to some common causes and tests that need to be performed to further clarify the diagnosis. The most likely causes: 1. Asthma, which is the most common cause of chronic cough. This condition is cough variant asthma, which is often a dry cough without sputum, paroxysmal and irritable, more frequent or aggravated at night and in the morning. 2. Postnasal drip syndrome, often with a heavy cough when lying down, may feel a flow of fluid from the back of the nose into the pharynx. 3.Esophageal reflux, often coughing or wheezing heavily during the day, especially after meals. There are mostly symptoms of gastroesophageal diseases such as heartburn, belching and acid reflux. 4.Taking certain drugs against hypertension can cause coughing, mainly angiotensin-converting enzyme inhibitors, such as mercaptoproline, and beta-blockers, such as betalactam. Therefore, these drugs should be discontinued for those with related conditions. 5. Tumors, in addition to irritable cough, may also be accompanied by hemoptysis, especially in patients over 40 years of age who have smoked a lot for a long time and have a small amount of blood in their sputum. 6. Endobronchial tuberculosis, which is an aggressive cough, may also have a low fever and other manifestations of tuberculosis. 7. Chronic bronchitis, bronchiectasis, and other infectious diseases. There is often sputum, yellow pus sputum or green pus sputum. 8. Allergic cough, which may not develop into asthma, may be accompanied by other allergic diseases. It is a dry cough, without wheezing and dyspnea, with normal airway reactivity and normal chest X-ray. It often occurs after so-called exposure to allergic factors, but also after a cold. Tests that need to be done: 1, lung imaging, chest X-ray first, if there are suspicious shadows, lung CT or even lung enhancement CT may be done. 2, lung function and diastolic test, if no obvious abnormalities are seen in lung imaging, it is advisable to do this test. 3.Sinus CT, it is advisable to do this examination for those who are suspected of postnasal drip syndrome. 4.Fiber bronchoscopy, which is recommended for patients suspected of having tumor, bronchial endothelial tuberculosis, etc. 5.Allergen test can be performed for suspected asthma and allergic cough. 6. 24-hour esophageal pH monitoring, which can be considered for patients suspected of having esophageal reflux if necessary. Because this test can only be done in a few hospitals and is very troublesome. If the test cannot be done, a trial of medication for esophageal reflux can be considered.