Infants spitting up yellow milk may be caused by physiological factors or pathologic factors such as indigestion and acute gastroenteritis. 1. Physiological factors: the child’s stomach is horizontal, the stomach capacity is limited, after eating milk may lead to overflow, spit up and so on. As the milk stays in the stomach for a long time, the casein in it combines with the stomach acid to form a precipitate, which may appear yellow. 2. Indigestion: Indigestion is one of the most important causes of vomiting in children, which can also result in yellow colored milk, accompanied by abdominal distension and changes in stool characteristics, such as the appearance of milk petals in the stool. 3. Acute gastroenteritis: In acute gastroenteritis, babies can vomit yellow milk and have diarrhea, fever, crying and restlessness. Infants vomiting yellow milk may also be caused by other factors such as intestinal obstruction, it is recommended to consult a doctor in a timely manner, improve the examination, and cooperate with the doctor to take appropriate measures or treatment.