Newborn smile can be caused by physiological phenomenon, congenital stupidity, developmental delay and other reasons. 1. Physiological phenomenon: the newborn’s brain and the nervous system in the organism are not fully developed, when the nervous system is too excited, there will be some unconscious expressions, movements, if the reflex appears in the cheeks, it can lead to the newborn’s smile smile. 2. Congenital stupidity: it will make the development of newborns appear delayed, may appear mental retardation, facial abnormalities and other phenomena, it will lead to the symptoms of the newborn’s smile. 3. Developmental delay: If the brain tissue cells of the newborn, the nervous system abnormalities make the newborn developmental delay, so that the newborn’s mental retardation, it will lead to the newborn smile. Newborns smile, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.