Atopic cough: This type of cough refers to a cough with other symptoms or signs that are suggestive of an atopic cause, i.e., the cough is a symptom of one of these clearly diagnosed diseases. For example, cough with expiratory dyspnea, prolonged expiratory phase on auscultation or croup suggests intrathoracic airway pathology such as tracheobronchitis, asthma, congenital airway developmental abnormalities (e.g., tracheobronchial softening), etc.; cough with shortness of breath, hypoxia or cyanosis suggests pulmonary inflammation; cough with growth disorders, pestle fingers (toes) suggests severe chronic lung disease and congenital heart disease, etc.; cough with pus sputum suggests pulmonary inflammation In cases with hemoptysis, severe lung infection, pulmonary vascular disease, pulmonary ferritinosis or bronchiectasis are suggested. Non-specific cough This type of cough refers to chronic cough in which cough is the main or only manifestation and no significant abnormalities are seen on chest X-ray. This is the main type of chronic cough, also known as “narrow chronic cough”. Respiratory tract infections and post-infection coughs Respiratory tract infections caused by pathogenic microorganisms are a common cause of chronic cough in children, mostly in preschool children <5 years of age. Acute respiratory infections with cough symptoms lasting more than 4 weeks can be considered post-infectious cough. The mechanism may be disruption of airway epithelial integrity and/or squamous metaplasia of ciliated epithelial cells and/or persistent airway inflammation with temporary airway hyperresponsiveness as a result of the infection. The clinical features and diagnosis of post-infectious cough are based on: (i) a clear recent history of respiratory infection; (ii) an irritating dry cough or a small amount of white mucous sputum; (iii) no abnormalities on chest X-ray; (iv) normal pulmonary ventilation; (v) a cough that is usually self-limiting; and (vi) no other cause of chronic cough. If the cough persists for more than 8 weeks, other diagnoses should be considered. This disease is a delayed or persistent bacterial infection of the conducting airways, with a persistent "wet" cough as the main clinical feature. The diagnosis is based on a chronic wet cough lasting more than 4 weeks, effective antibiotic therapy, and the exclusion of other respiratory diseases. When the patient is suspected of having this disease, bronchoscopy may be performed to obtain an etiologic basis. The common pathogens are Haemophilus influenzae undetermined, Pneumococcus pneumoniae, and Moraxella mucosae. Cough variant asthma (CVA) CVA is one of the common causes of chronic cough in our children, especially in preschool and school-age children. The clinical features and diagnosis of CVA are based on: ① persistent cough >4 weeks, often with episodes at night and/or early morning, aggravated by exercise and cold air, without clinical signs of infection or ineffective after prolonged antibiotic treatment; ② diagnostic treatment with bronchodilators can result in significant relief of cough symptoms; ③ normal pulmonary ventilation function and bronchial excitation tests suggesting airway hyperresponsiveness; ④ history of allergic diseases including a history of drug allergy and a positive family history of allergic diseases, of which a positive allergen test can assist in the diagnosis; ⑤ chronic cough caused by other diseases, among others. Upper airway cough syndrome (UACS) Various rhinitis, sinusitis, chronic pharyngitis, chronic tonsillitis, nasal polyps, adenoid hypertrophy, and other upper airway diseases can cause chronic cough, as well as a previous diagnosis of postnasal drip (flow) syndrome. It is now recognized that lesions in other parts of the upper airway besides nasal disease can also cause persistent cough in children, so the diagnostic name UACS has been used instead. The clinical features and diagnosis of UACS are: (1) chronic cough with or without sputum, which is worse in the early morning or when the position is changed, often accompanied by nasal congestion, runny nose, dry throat with foreign body sensation, repeated clearing of the throat, and a feeling of mucus adhesion to the posterior pharyngeal wall, with a few children complaining of headache, dizziness, and low fever; (2) examination of the sinus area may be painful, and there may be yellowish-white discharge from the sinus opening. (3) Targeted treatment such as antihistamines and leukotriene antagonists, and nasal glucocorticoids are effective; (4) If the sinusitis is caused by sinusitis, the corresponding changes can be seen on sinus X-ray or CT film. Gastroesophageal reflux cough (GERC) Gastroesophageal reflux (GER) is a physiological phenomenon in infancy and early childhood. The incidence of GER in healthy infants is 40% to 65%, peaking at 1 to 4 months of age and mostly resolving spontaneously at 1 year of age. GERC becomes a disease when it causes symptoms and/or is accompanied by gastroesophageal dysfunction, i.e., gastroesophageal reflux disease. The clinical features and diagnosis of GERC include: (1) paroxysmal cough, sometimes severe, mostly at night; (2) symptoms mostly appear after eating and drinking, with feeding difficulties, some children with abdominal or subxiphoid discomfort, burning sensation behind the sternum, chest pain and sore throat; (3) in addition to causing cough, infants may also suffer from asphyxia, bradycardia and an arched back; (4) it may lead to arrested or delayed growth of the child. Eosinophilic bronchitis (EB) EB is considered to be an important cause of chronic cough in adults, but its incidence in children is unclear. The clinical features and diagnosis of EB are based on: (i) chronic irritant cough; (ii) normal chest X-ray; (iii) normal lung ventilation without airway hyperresponsiveness; (iv) relative percentage of eosinophils in sputum > 3%; and (v) effective treatment with oral or inhaled glucocorticoids. Congenital respiratory disease This disease is mainly seen in infants and young children, especially in children less than 1 year old. They include congenital tracheoesophageal fistula, congenital vascular malformation compressing the airway, laryngotracheobronchial softening and/or stenosis, bronchopulmonary cysts, ciliary dyskinesia, and mediastinal tumors. These disorders are often misdiagnosed as asthma. Psychogenic cough This condition is not very rare in childhood, but the diagnosis is made only when tic disorders are excluded and the cough improves with behavioral interventions or psychotherapy. Also, cough features are only suggestive of psychogenic cough. The clinical features and diagnosis of psychogenic cough are based on: (1) the prevalence in older children; (2) the predominance of a daytime cough that disappears when focused on an event or at nighttime rest; (3) the frequent presence of anxiety symptoms; and (4) the absence of organic disease and the exclusion of other causes of chronic cough. Other causes Foreign body inhalation Cough is the most common symptom following foreign body inhalation in the airway, and foreign body inhalation is an important cause of chronic cough in children, especially those aged 1 to 3 years. This cough usually presents as a violent paroxysmal choking cough, or it can simply present as a chronic cough with obstructive emphysema or atelectasis. Once the foreign body enters the area below the small bronchi, it enters the “silent zone” and may not cough. Some children with renal hypertension have a cough induced by the use of angiotensin-converting enzyme inhibitors (ACEIs), which usually cause a chronic, persistent dry cough that is worse at night or when lying down, and which can be significantly reduced or even disappeared after 3-7 days of discontinuation. In addition, β-adrenergic receptor blockers can also cause bronchial hyperresponsiveness and therefore may also lead to drug-induced cough. Otogenic cough 2% to 4% of the population have vagal ear branches. When lesions occur in the middle ear in this group, the vagus nerve becomes irritated and causes a chronic cough. This type of cough is one of the rare causes of chronic cough in children.