The physiological causes of neonatal vomiting are closely related to the fact that the sphincters of their digestive system have not yet developed properly.
The human stomach has two doors, the cardia and the pylorus. The cardia is the entrance to food, and under the action of the sphincter, it opens automatically when we eat and closes naturally at the end of the meal. The newborn baby’s body is not yet fully developed, the mucous membrane of the oesophagus is tender and the sphincter is loose. When the stomach starts to move and the internal pressure increases, the cardia will open accidentally, causing the milk to reflux back into the oesophagus and finally into the mouth, resulting in the baby spitting up. Physiological causes of spitting up will gradually improve as the baby grows up.