I. Classification of coughs Coughs are usually divided into 3 categories according to time: acute cough, subacute cough and chronic cough. Acute cough lasts <3 weeks, subacute cough is 3 to 8 weeks, and chronic cough is >8 weeks. Coughs can be subdivided by nature into dry and wet coughs. Different types of cough have different distribution characteristics. Chronic cough has more causes and is usually divided into two categories according to the presence or absence of abnormalities in chest X-ray examinations: one category is those with clear lesions on X-ray chest films, such as pneumonia, tuberculosis, bronchopulmonary cancer, etc. The other category is those with no obvious abnormalities on X-ray chest films and cough as the main or only symptom, which is usually referred to as chronic cough of unknown origin (chronic cough for short). II. History and ancillary examinations Careful history taking and physical examination can narrow the diagnosis of cough, provide clues to the etiology of the diagnosis, and even lead to a preliminary diagnosis and empirical treatment, or select relevant examinations based on the present history to clarify the etiology.