I. The concept of recurrent respiratory infections Recurrent respiratory infections are one of the common diseases in children, especially in infants and young children. All children aged 0 to 2 years old, suffering from upper respiratory tract infection greater than or equal to 7 times per year, 2 to 6 years old greater than or equal to 6 times, 6 to 12 years old greater than or equal to 5 times; the above age groups suffering from lower respiratory tract infection greater than or equal to 3 times, 2 times, 2 times per year, respectively, are called recurrent respiratory infections. However, it should be noted that: 1. 1 year of observation is required; 2. 7 days or more must elapse between two episodes of upper respiratory tract infection; 3. Foreign countries stipulate that children of any age are considered to have recurrent respiratory infections if they have more than 10 episodes of upper sensation or more than 3 episodes of lower sensation per year, or if a respiratory infection lasts more than 1 month. Second, the causes of recurrent respiratory infections 1, pediatric immune system and mechanical barrier function are not well developed, the nasal mucosa is delicate, lack of nasal hair, commonly used mouth breathing, easy to choke, such as low levels of serum immunoglobulin, due to 6 months after the infant, in the period of physiological immune depression, more prone to respiratory infections. 2, congenital diseases: congenital heart disease, pulmonary insufficiency, esophageal tracheal fistula, etc. 3, viruses and other infections cause temporary immune deficiency in children, such as chickenpox, measles, mumps, etc., which can cause thymus atrophy, imbalance between T-cell subpopulations, and reduced resistance. This secondary immune depression takes 1 to 2 months to gradually recover. 4, Chronic bacterial lesions, such as tonsillitis, sinusitis, otitis media, bronchitis, etc., damage the respiratory mucosa and impair the immune function of the body. 5, malnutrition and chronic wasting diseases, such as rickets, nutritional anemia, zinc and other trace element deficiencies and vitamin A, C and other deficiencies, also affect the body’s immune function. In addition, chronic nephritis, kidney disease, chronic diarrhea, tuberculosis, various tumors, etc., also make the body’s resistance to decline. 6, immunosuppressants: such as long-term use of large amounts of glucocorticoids, cyclophosphamide, methotrexate, etc. can inhibit the body’s immune function susceptible to respiratory infections. 7, environmental factors: such as air pollution, damp, dark, crowded living environment can damage the airway mucosa, reducing the respiratory resistance and immune function susceptible to respiratory tract infections. Some studies have pointed out that the incidence of recurrent respiratory infections is 20 times higher in children in families where coal is the main fuel than in the control group, as is passive smoking. 8. Other: Children who are not properly cared for, incompletely treated for respiratory infections and living in crowded and poorly sanitized group institutions are also susceptible to recurrent respiratory infections. The relationship between recurrent respiratory tract infections and asthma has been shown that 85% of children with asthma have respiratory tract infections as their first cause and recurrent cause, so it is important to actively prevent and treat respiratory tract infections and reduce their incidence to reduce the occurrence and recurrence of asthma.