Infants not pooping for two days can be a normal physiological phenomenon, or it can be caused by functional constipation, congenital megacolon and other reasons. 1. Physiological phenomenon: If an infant does not poop for two days occasionally, without other abnormalities, it is considered a normal phenomenon. 2. Functional constipation: If the baby often does not poop for two days, or accompanied by abdominal distension, poor appetite and other discomforts, it may be caused by functional constipation, parents can help to carry out abdominal massage, and if necessary, can be prescribed by the application of probiotics (such as Bacillus subtilis bacillus granules), keserol and other medications. 3. Congenital megacolon: If an infant has congenital megacolon, he or she will have more stubborn constipation, and as the disease progresses, the frequency of bowel movements will decrease. If the baby often does not poop for two days, it should go to the hospital in time, in order to clarify the cause of the disease and standardize the treatment.