Newborns spit up with sour odor considerations related to physiological factors, may also be indigestion, intestinal dysfunction and other factors lead to. 1. physiological factors, newborns spit out a sour smell may be due to the newborn’s gastrointestinal tract is not fully developed, intestinal function is poor, food is not fully digested and absorbed, so there may be newborns spit out a sour smell symptoms. 2. indigestion, clinically indigestion due to the digestive capacity is affected, may lead to food fermentation, milk petals, bloating, resulting in newborns spit up with sour odor symptoms. 3. intestinal dysfunction, some newborns have intestinal dysfunction due to weak gastrointestinal function, may lead to this symptom. Newborns spit up with a sour odor may also have other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, to give targeted treatment or treatment.