9 months baby nausea spitting up may be physiological phenomenon, incorrect feeding style, gastrointestinal diseases and other reasons. 1. Physiological phenomenon: 9-month-old babies are prone to gastroesophageal reflux (GERD) due to the incomplete development of the cardia sphincter at the lower end of the esophagus and its poor control ability. It is a normal physiological phenomenon and will get better with age without special treatment. Usually try to eat less and more meals, do not feed too much at one time to avoid nausea and spitting up. 2. Incorrect feeding: During feeding, the nipple or teat may touch the wall of the throat, thus leading to nausea and spitting up, you can try to change the nipple and other ways to relieve the symptoms. 3. gastrointestinal diseases: common gastritis, intestinal obstruction, etc., the baby may have abdominal pain, nausea, vomiting and other symptoms, the need for timely medical attention. Nausea and spitting up of 9-month-old babies may also be caused by other reasons, if it is not better for a long time, it is recommended to consult a doctor as soon as possible, and follow the doctor’s instructions for treatment.