Cough is one of the most common symptoms of respiratory diseases in children. Based on the duration of the illness, children’s cough is classified as acute (less than 2 weeks), prolonged (2-4 weeks) and chronic (more than 4 weeks). Chronic cough can be divided into atopic cough, where cough is accompanied by other symptoms or signs suggestive of an atopic cause, i.e. cough is one of these diagnostic symptoms of disease, and non-atopic cough, where cough is the main or only manifestation and no significant abnormalities are seen on chest radiographs. Chronic cough in children is defined as cough as the main or only clinical manifestation, with a duration of >4 weeks and no significant abnormalities on chest radiographs. Common causes of chronic cough in children of different ages 1. Cough variant asthma (CVA): CVA is the most common cause of chronic cough in children in China, especially in preschool and school-age children. Clinical features and diagnostic clues of CVA: (1) persistent cough for >4 weeks, usually dry, often at night and/or early in the morning, aggravated by exercise or cold air, without clinical signs of infection or ineffective after prolonged antimicrobial therapy; (2) significant relief of cough symptoms with diagnostic bronchodilator therapy; (3) normal pulmonary ventilation, with bronchial excitation tests indicating airway hyperresponsiveness (4) History of allergic disease and positive family history of allergic disease. (4) History of allergic diseases and positive family history of allergic diseases. A positive allergen test may assist in the diagnosis; (5) Chronic cough caused by other diseases are excluded. 2. Upper airway cough syndrome (UACS): UACS is the second leading cause of chronic cough in children, especially in preschool and school-age children. Various rhinitis, sinusitis, chronic pharyngitis, palatine tonsil and/or proliferative hypertrophy, nasal polyps, and other upper airway diseases may cause chronic cough. until 2006, the diagnostic name for UACS was postnasal drip (flow) syndrome (PNDs). The clinical features and diagnostic clues of UACS are: (1) persistent cough for >4 weeks with white foamy sputum (allergic rhinitis) or yellow-green pus sputum (sinusitis), which is worse in the morning or with changes in position, accompanied by nasal congestion, runny nose, dry throat with foreign body sensation and repeated throat clearing; (2) marked follicular hyperplasia of the posterior pharyngeal wall, sometimes with cobblestone-like changes, or with mucus-like or purulent secretions; (3) antihistamines, leukotripsy, and other drugs. (3) antihistamines, leukotriene antagonists and nasal glucocorticoids are effective for chronic cough caused by allergic rhinitis, while chronic cough caused by purulent sinusitis requires antimicrobial therapy for 2-4 weeks; (4) nasopharyngolaryngoscopy or lateral head and neck radiographs, sinus x-rays or CT films may be useful for diagnosis. (3) Post-infectious cough (PIC): PIC is a common cause of chronic cough in young children and preschoolers and has the highest rate of diagnostic correction among the causes of chronic cough in children. The clinical features and diagnostic clues of PIC are: (1) a recent clear history of respiratory infection; (2) a cough lasting >4 weeks with an irritating dry cough or a little white mucous sputum; (3) no abnormalities on chest radiographs or only increased texture in both lungs; (4) normal pulmonary ventilation or a transient airway hyperresponsiveness; (5) a cough that is usually self-limiting, but if it lasts longer than 8 weeks, other diagnoses should be considered (5) The cough is usually self-limiting, but if the cough lasts longer than 8 weeks, other diagnoses should be considered; (6) except for other causes of chronic cough. (4) Allergic (allergic) cough (AC): Some children with chronic cough are clinically atopic and are effectively treated with antihistamines and glucocorticoids, but they do not have bronchial asthma, CVA or NAEB. AC Clinical features and diagnostic clues: (1) cough lasting >4 weeks with an irritating dry cough; (2) normal pulmonary ventilation and negative bronchial excitation test; (3) increased sensitivity of cough receptors; (4) history of other allergic diseases, positive allergen skin test, elevated total and/or specific serum IgE; (5) chronic cough from other causes excluded.