Bronchial asthma is a chronic inflammatory disease of the airways involving a variety of cells, including inflammatory cells (eosinophils, mast cells, T lymphocytes, neutrophils, etc.), airway structural cells (airway smooth muscle cells and epithelial cells, etc.) and cellular components. This chronic inflammation leads to airway hyperresponsiveness in susceptible individuals, and when exposed to physical, chemical, biological and other stimuli, widespread and variable reversible airflow limitation occurs, resulting in recurrent episodes of wheezing, coughing, shortness of breath, chest tightness, etc., often occurring or worsening at night and/or early in the morning, and most children can be treated for remission or resolve on their own. Bronchial asthma is the most common chronic disease in childhood, and the prevalence of childhood asthma in China has been increasing significantly in the last decade or so, which seriously affects the physical and mental health of children and also brings heavy mental and economic burdens to families and society. Children are in the process of growth and development, and the clinical phenotype of asthma varies among children of all ages due to the different anatomical, physiological, fatigue-free and pathological characteristics of the respiratory system. The diagnosis and treatment methods of asthma are different due to the different response to drug therapy and the degree of coordination and cooperation. 1.Diagnostic criteria of bronchial asthma 1.Recurrent attacks of wheezing, cough, shortness of breath and chest tightness, mostly related to exposure to allergens, cold air, physical and chemical stimuli, respiratory tract infections and exercise, etc., often occurring or intensifying at night and/or early in the morning. 2.Dispersive or diffuse, expiratory-phase croup can be heard in both lungs during the attack, with prolonged expiratory phase. 3.The above signs and symptoms are effective with anti-asthma treatment or resolve on their own. 4.Except wheezing, cough, shortness of breath and chest tightness caused by other diseases. 5.In case of atypical clinical manifestations (e.g., no obvious wheezing or croup), at least one of the following should be present: (1) Positive bronchial excitation test or exercise excitation test; (2) Confirmation of reversible airflow limitation: ① Positive bronchodilator test: 15 min increase in first second expiratory volume (FEV1) after inhalation of rapid-acting β2 agonist [such as salbutamol (SalbutamoI)] Increase ≥ 12% ② Effective anti-asthma treatment: Increase in FEVl ≥ 12% after 1 to 2 weeks of treatment with bronchodilators and oral (or inhaled) glucocorticoids; (3) Maximum expiratory flow (PEF) daily variability (continuous monitoring for 1-2 weeks) ≥ 20%. Those who meet the l to 4 or 4 or 5 can be diagnosed as asthma. II. Characteristics of wheezing in children under 5 years of age 1. Clinical phenotype and natural course of wheezing in children under 5 years of age: wheezing is a very common clinical manifestation in preschool children, and recurrent wheezing can occur in non-asthmatic preschool children. Wheezing in children under 5 years of age can be classified into 3 clinical phenotypes: (1) Early transient wheezing: Mostly seen in premature births and parental smokers, wheezing is mainly due to environmental factors that delay lung development. (2) Persistent wheezing with early onset (before the age of 3 years): Children mainly present with recurrent wheezing associated with acute respiratory viral infections, with no atopic manifestations and no family history of allergic diseases. Wheezing symptoms usually persist until school age, and some children remain symptomatic at 12 years of age. In children younger than 2 years of age, the cause of wheezing episodes is usually associated with infections such as respiratory syncytial virus, and in children older than 2 years of age, it is often associated with other viral infections such as rhinovirus. (3) Delayed wheezing/asthma: These children have a typical atopic background, often with eczema, asthma symptoms often delayed and persistent into adulthood, and airways with typical asthma pathology. It should be noted, however, that types 1 and 2 of childhood wheeze can only be identified by retrospective analysis. Early intervention in childhood wheezing facilitates disease control and therefore it is not advisable to classify patients as such at the time of initial treatment. Evaluation of wheezing in children under 5 years of age: More than 80% of asthma starts before the age of 3 years, and in patients with persistent asthma with pulmonary impairment, the impairment often starts in preschool, so it is necessary to identify children who are likely to develop persistent asthma from among wheezing preschoolers for effective early intervention. However, there are no specific tests or indicators that can be used to make a definitive diagnosis of asthma in preschool wheezing children. A diagnosis of asthma is highly indicated in children with the following clinical features: (1) frequent episodes of wheezing more than once a month; (2) activity-induced cough or wheezing; (3) intermittent nocturnal cough not caused by a viral infection; (4) wheezing that persists beyond 3 years of age. Asthma Predictor Index: can be used effectively to predict the risk of developing persistent asthma in wheezing children within 3 years of age. Asthma prediction index: ≥4 wheezing episodes in the past 1 year, with 1 major risk factor or 2 minor risk factors, is considered positive for asthma prediction index and recommended to be treated as asthma. Primary risk factors include: (1) parental history of asthma; (2) physician diagnosis of atopic dermatitis; (3) evidence of inhalation allergen sensitization. Secondary risk factors include: (1) evidence of food allergen sensitization; (2) peripheral blood eosinophils ≥4%; and (3) wheezing unrelated to the flu. It is important to emphasize that the majority of preschool children with wheezing have a good prognosis and their asthma-like symptoms may resolve spontaneously with age. Therefore, these children must be reevaluated periodically (3-6 months) to determine the need for continued antiasthmatic therapy. The diagnosis of cough variant asthma is one of the most common causes of chronic cough in children, with cough as the only or main manifestation, without significant wheezing. The diagnosis is based on: (1) cough lasting >4 weeks, often with nocturnal and/or early morning attacks or exacerbations, with a predominantly dry cough; (2) no clinical signs of infection or ineffective after prolonged antibiotic treatment; (3) effective diagnostic treatment with anti-asthmatic drugs; (4) exclusion of other causes of chronic cough; (5) positive bronchial excitation test and/or daily variability of PEF (continuous monitoring for 1 to 2 weeks) ≥20%; (6) positive bronchial excitation test and/or daily variability of PEF (continuous monitoring for 1 to 2 weeks) (5) positive bronchial excitation test and/or PEF daily variability rate (continuous monitoring for 1 to 2 weeks) ≥ 20%; (6) personal or first- or second-degree relative history of atopic disease, or positive allergen test.