Babies who fall asleep and spit up milk are often associated with gastroesophageal reflux, pyloric spasm, coughing, air inhalation, cold and fever, etc. When babies are younger, they fall asleep and spit up milk, which is a normal physiological phenomenon. The main reason is that when a baby is born, the lower sector of the esophagus is not very mature and has poor control over gastroesophageal reflux, which will slowly disappear as the baby grows. In addition, the baby’s stomach is horizontal during infancy and the function of autonomic regulation is poor, which makes it easy for pyloric spasm to occur, leading to spitting up of milk. There are also many new mothers who feed their babies in an improper position, causing them to suck in too much air while breastfeeding. The air will be above the stomach when it enters the stomach, and the air will be easily ejected from the mouth with the milk, causing the baby to spit up after falling asleep. Pathological factors can also cause your baby to spit up, such as when your baby coughs more violently and frequently, the sputum is not easily coughed out, leading to spitting up. When a baby has a cold and fever, it can cause abnormal peristalsis in the gastrointestinal tract, such as when the gastrointestinal tract is congested or edematous, which can affect the baby’s digestion and absorption and cause vomiting.