Newborn breathing through the mouth may be a normal physiological phenomenon, but it may also be abnormal pathological phenomena, such as upper respiratory tract infection, nasal developmental abnormalities. 1. Physiological phenomenon: Because the respiratory system of newborns is not well developed, in addition to breathing through the nose will also be through the mouth to assist breathing, and newborns sometimes because of crying and noisy resulting in an increase in oxygen demand, there may also be the phenomenon of open-mouthed breathing, mostly normal physiological phenomena. 2. Pathological phenomena: (1) upper respiratory tract infection: if the baby has upper respiratory tract infection, the mucous membrane of the nasal cavity will have inflammation, swelling, congestion, and increased secretion, resulting in nasal congestion, so it will also use the mouth to breathe. (2) Abnormal nasal development: If the baby’s nasal development is abnormal, such as congenital deviated nasal septum, congenital posterior nostril atresia, etc., it will also lead to blockage of the nasal cavity, which will cause the nasal cavity to breathe poorly and exhale through the mouth. If a newborn baby exhales through the mouth for a longer period of time or is accompanied by other uncomfortable symptoms, it is recommended that parents take the baby to a regular hospital for consultation in order to make a clear diagnosis and timely treatment.