The dangerous factors of children's asthma are diverse, some are from themselves, some are decided by the external environment and performance and they are totally different.There are some factors:
（1）The tree structure and pulmonary function of bronchus: Fundamental lung function of infants and young children have an important effect on the severity of asthma attack. Airway conductance rate is low for the infants in the early period, so the opportunity of suffering from asthmatic disease for one year old is higher than normal children by 3 ~ 6 times,and the dangerous factors won't go away until three. Preschool children are prone to respiratory viral infection, one of the important factors is the narrow small airway, so it's easy to cause airway obstruction and hyperventilation after the infection.
（1）The tree structure and pulmonary function of bronchus: Fundamental lung function of infants and young children have an important effect on the severity of asthma attack. Airway conductance rate is low for the infants in the early period, so the opportunity of suffering from asthmatic disease for one year old is higher than normal children by 3 ~ 6 times,and the dangerous factors won't go away until three. Preschool children are prone to respiratory viral infection, one of the important factors is the narrow small airway, so it's easy to cause airway obstruction and hyperventilation after the infection.
（2）Allergy: Allergic person can cause allergic reaction if repeatedly exposure to pollen, dust mites and animal dander. This is a kind of special organization pathological immune response involving the local or systemic,it can lead to dysfunction or tissue injury of organ involved,and causes some allergic diseases, especially type I allergic diseases, such as asthma, allergic rhinitis, urticaria, eczema etc.. allergy is often caused by gene,if parents (or grandparents, grandparents) is allergic.
（3）Family history of asthma:If you ask the family history of the allergic asthmatic children,itcan be found that most of the families have asthma or other allergic diseases,which suggests the onset of allergic asthma is associated with genetic factors.
（4）The sex of the asthma children also seems to play a role,male infants are more like to get the respiratory tract disease, age and sex relations with asthma are still not very clear.
The prevalence of asthma in children of boys and girls in China is 1.17% and 0.82%,so the difference is significant.
（5）Immune response to viral infection :The virus infection in infants and young children has a strong immune response,and it can cause severe inflammation and airway reactivity increased,to increase the risk of asthma.
（6）Airway hyperresponsiveness:Virus infections in infants and young children occur bronchial epithelial damage. Lung function is reversible or irreversibly damaged,leading to increase airway responsiveness.Infant hospitalized patients with bronchiolitis in children often have reduced pulmonary ventilation function and airway reactivity increases.
