Cough can be divided into dry cough and wet cough by nature. A dry cough is a cough without sputum, or a cough with very little sputum, which is not easily expelled. The most common cause is upper respiratory tract infection, the common cold. Other common causes are acute sinusitis, allergic rhinitis, acute bronchitis, acute attacks of chronic bronchitis, and bronchial asthma. A cough that lasts more than 3 weeks and less than 2 months is called a subacute cough. At this time, you need to go to the hospital for examination, and the common causes include post-infectious cough, upper airway cough syndrome, and bronchial asthma. A dry cough of longer than 2 months with an unclear cause is called chronic cough and has the following four common causes: upper airway cough syndrome, cough variant asthma, gastroesophageal reflux and chronic bronchitis. In addition, lesions in the stomach and esophagus can also cause a dry cough. There are many reasons for this, which need to be combined with clinical manifestations, positive findings on physical examination, and ancillary tests to gradually investigate.