The first step is to find out whether your baby is spitting up or spilling milk, both of which have different meanings and different causes and treatments. Spitting up can happen soon after feeding or half an hour later, and the child has an open-mouthed, painful expression before spitting up. Spitting up is less frequent and occurs when the child has just finished feeding, and usually stops after one or two mouthfuls. Spitting up is a common phenomenon in infants and can be caused by two factors: first, it is a symptom of systemic or gastrointestinal diseases; second, the anatomical and physiological characteristics of infants’ gastrointestinal head are prone to spitting up. In general, spitting up is more common due to the second cause. The milk eaten by the mouth first passes through a tube called the esophagus and then enters the stomach. The stomach has two doors, one is connected to the esophagus called the cardia, the entrance of the stomach, and the other is connected to the intestine called the pylorus, the exit of the stomach. The tension of the esophageal muscles in infants and young children is low, which can easily cause dilation, while peristalsis is slower, so food is easily sloughed off. The cardia is more relaxed, not closed tightly, easy to be washed away by food. When there is a little more food in the stomach, the cardia can be flushed open and backflow back into the esophagus. The pylorus is tightly closed, easily stimulated by food and spasm, so that the outlet resistance is greater, food through the slow or difficult to pass, the food from the pylorus reflux to the cardia, breaking the door out. In addition, the baby’s stomach does not hang down like older children and adults, but is in a horizontal position. This makes the stomach smaller and holds less food, and it is also easy to return to the cardia. Due to all these factors, even under normal circumstances, when the baby is lying down immediately after eating too much milk, the milk will easily open the cardia and return to the mouth through the esophagus, causing vomiting. If a child spits up once in a while and is in good spirits, it is not necessarily a disease. If the child spits up several times in a row, or at every feeding, you should pay attention to whether the child has a fever, how the stools are, and whether there is any change in the child’s spirit. There may be problems in the gastrointestinal tract itself, or there may be lesions in other systems, and the child should be taken to the hospital for examination. Most of the time, the milk is sucked into the baby’s stomach. When air enters the stomach, the gas is lighter than the liquid and is located above, so it easily rushes out of the cardia and also brings out some milk, which causes the milk to ripple. Therefore, when breastfeeding, let the child’s mouth wrap around the entire nipple and do not leave a gap to prevent the air from entering by mistake. When feeding with a bottle, you should also let the milk completely fill the nipple, not just half of the nipple for fear that the milk will be too rushed, so that it will be easy to suck in air. After feeding, it is best to let the child lie on the adult’s shoulder and pat the child’s back with your hand, so that the sucked-in air can run out. After feeding, pick up and put down the child with gentle movements and less movement. If you shake your child too much, he or she will easily spill milk or spit up. The amount of milk that comes out is usually small and will not have much effect on your child’s growth and development. As the child grows older, it will naturally get better.