Sour smell of spit-up in babies suggests that babies have indigestion. The causes of indigestion in babies may be normal, related to small stomach capacity and improper feeding, or may be caused by gastrointestinal inflammation. As the baby is weak and spitting up will affect the baby’s nutrient absorption, so if there is frequent spitting up, or the sour smell is obvious, you should go to the hospital for help and treatment after clarifying the cause. Common causes are as follows: 1. Physiological factors: 1. Small stomach capacity: mostly occurs in infants born 1-2 months old, mainly due to the small stomach capacity of infants at this time, the gastrointestinal tract function is not yet mature, can not fully digest the ingested milk, the body a force, not yet fully digested milk due to increased negative pressure spit out, and there is a sour smell. It is recommended that parents feed the baby a small amount of times and pat the baby’s back after feeding, so that the gas in the baby’s stomach is expelled; 2. Improper feeding: the gastrointestinal tract of infants is weak, and when there is improper feeding such as feeding too fast, too much milk, improper feeding posture, etc., the infant is unable to digest in time, resulting in vomiting and a sour odor, in addition to reduced food intake, hyperintestinal sounds, diarrhea and other symptoms. In mild cases, hot compresses and massage of the abdomen can relieve, if not relieved by medical advice to be pediatric elimination granules, probiotics and other drugs to relieve indigestion. Second, the pathological factors: feeding baby milk powder is not clean, cold or placed too long to deteriorate, the baby may cause gastrointestinal inflammation after eating, vomiting milk with sour smell, accompanied by diarrhea, abdominal pain and other symptoms, should promptly seek medical attention, according to the patient’s condition to give oral medication, such as montelukast, etc., dehydration in serious cases to give rehydration treatment. When parents feed their babies, they can take less and more meals, control the feeding speed, turn the baby appropriately when feeding, and pay attention to the weather changes to increase the baby’s clothes and reduce the blanket in time.