Nine-month-old babies spit up milk, usually for the following reasons: First, the most common is physiological gastroesophageal reflux, because the nine-month-old baby’s cardia is not well developed, the stomach volume is small, the pylorus is relatively well developed, so it is easy to spit up milk. Secondly, it is important to note that if you often spit up milk, have eczema and poor digestion, consider whether you have food allergies, milk protein allergy is common in milk feeding, egg allergy is also more common with the addition of complementary foods, and breastfeeding is related to the mother’s diet. Third, if the vomiting is only acute, it is most common after acute gastroenteritis, viral or bacterial infections, or other systemic infections, such as pneumonia, which can present digestive symptoms and cause vomiting. Fourth, if the vomiting is particularly pronounced, especially in the form of jet vomiting, attention should be paid to intracranial problems, such as intracranial occupancy, increased intracranial pressure caused by meningoencephalitis leading to vomiting, and also to surgical conditions such as intestinal obstruction causing vomiting.