If a two-year-old baby develops a cough in bed at night, if the child is found to have a stuffy nose, runny nose and sore throat during the day, the cough in bed at night is still caused by a respiratory infection. Once an infection occurs in the respiratory system, inflammatory exudate exudes from the respiratory tract, which can irritate the mucous membrane of the respiratory tract, resulting in coughing symptoms. At night the vagus nerve of the body tends to become excited, leading to bronchial constriction, which in turn can aggravate the cough, so that the symptom of coughing in bed at night can occur. It is possible that the child already has symptoms of airway hyperresponsiveness, and once the vagus nerve becomes excited at night, it leads to coughing. It is likely that airway hyperresponsiveness exists and is caused by cough variant asthma, which can be diagnosed with a bronchodilator test or bronchial excitation test. There is also a possibility that the air in the room is dry at night when the child is sleeping and breathing with the mouth open, which can easily irritate the airways and lead to coughing.