Infants with open-mouth breathing indicate that nasal ventilation is affected, mainly due to nasal stenosis or obstruction, and lung infections can also appear open-mouth breathing. 1. Nasal stenosis or obstruction: infants with upper respiratory tract infections or rhinitis can cause nasal congestion, adenoid hypertrophy of varying degrees can lead to nasal stenosis, all of which can lead to the symptoms of open-mouth breathing. 2. Lung infections: Lung infections can cause accelerated respiration and hypoxia, and when hypoxemia occurs, open-mouth breathing can occur. There may be other reasons for open-mouth breathing in infants, so it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.