Spitting up after breastfeeding can be caused by improper feeding, or gastroesophageal reflux, congenital megacolon and other diseases. 1. Improper feeding: If you eat milk too fast or swallow a lot of air when feeding, to a certain extent, the situation of spitting up after eating milk will occur. 2. Gastroesophageal reflux (GERD): The causes of GERD include impaired anti-reflux structure and function, reduced esophageal clearance, and reduced resistance of the esophageal mucosa. Since the patients will have typical symptoms such as heartburn, reflux and nausea, they may sometimes vomit after eating milk. 3. Congenital megacolon: The occurrence of this disease is related to the abnormal microenvironment of the intestinal wall, genetic inheritance, abnormal embryonic development and other reasons. Common symptoms are constipation, abdominal distension, vomiting, etc., and some patients will have the situation of spitting up after eating milk. Babies spit up after eating milk, there may also 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.