Forty days old baby stool with foam, mainly due to the following reasons: 1, breast milk contains more lactose, by the intestinal lactase decomposition of gas, foam in the stool, the baby no other discomfort, eating milk, sleep are good, weight growth as usual, as a normal physiological phenomenon, do not worry. 2, gastrointestinal tract dysfunction, abdominal cold may cause gastrointestinal tract dysfunction and indigestion, causing the phenomenon of foam in the stool. 3, intestinal infection, bacteria, viruses, parasites, fungi and other pathogens caused by intestinal infection, can lead to the phenomenon of bubbles. 3, intestinal infections, bacteria, viruses, parasites, fungi and other pathogens cause intestinal infections, can lead to the phenomenon of bubbles in the stool. 4, lactose intolerance, due to reduced intestinal lactase secretion, can not fully digest the decomposition of lactose in breast milk or cow’s milk caused by non-infectious diarrhea, the stool is mostly bubble stool. If your baby has foamy stools for a long time, go to the hospital for routine stool and stool pH check and treat under the advice of your doctor.