Breast milk is the best food for infants and young children, so it is generally recommended to exclusively breastfeed for 6 months, and then add complementary foods after 6 months. Breastfeeding diarrhea is mostly seen in small infants within 6 months of age, generally soon after birth, diarrhea, stools are mostly foamy and thin watery, sometimes containing milk flaps, occasionally green, also with strips of transparent mucus, the smell has a special sour odor. The stools are usually frequent, ranging from 3 to 20 times a day. However, the child is in good spirits, eats enough milk, and has normal weight gain. The typical characteristics are “eating, pooping, and growing at the same time”, and there are no abnormalities such as weight gain, choking, milk spillage, vomiting, bloating, abdominal pain, and crying after eating milk. If the baby has breast milk diarrhea, if the stool is slightly diluted and there is no disease manifestation, it usually does not need special treatment and will get better after adding complementary food. If breast milk diarrhea affects your baby’s growth and development, such as poor weight gain, reduced urine output, or frequent diaper dermatitis, you should add lactase to your baby before breastfeeding, which can promote the breakdown of lactose in breast milk and relieve breast milk diarrhea. However, if the baby has sudden onset of diarrhea within a short period of time, with a marked increase in the number of stools or containing mucus-purulent and bloody stools. At the same time, the child has a significantly reduced appetite, frequent vomiting, decreased urine output, frequent crying, fever, and eczema, this needs to be considered as other causes of diarrhea and requires prompt medical treatment.