Lactose intolerance, also known as lactase deficiency, is a disease caused by the lack of lactase or low lactase activity in the body and the inability to completely digest and absorb the lactose after consuming dairy products. Diarrhea: is a common and main symptom of lactose intolerance, which can be manifested as an increase in the number of bowel movements per day, mostly yellow or greenish egg-flake soup-like stools, foam and milk lumps can be seen in the stool, which can also be accompanied by an obvious sour odor; 2, hyperintestinal sounds: mostly due to increased gastrointestinal peristalsis, which can be manifested as a grunting sound in the abdomen, accompanied by increased exhaust; 3, bloating: indigestible lactose may be produced under the action of intestinal flora Gas, bloating symptoms; 4, abdominal pain: most of the pain is mild, a few babies can appear severe abdominal pain, the pain site is located in the upper abdomen, but the specific location is not fixed, pain characteristics can be burning pain, soreness or dull pain; 5, nausea and vomiting: relatively rare, may be due to unabsorbed lactose in the gastrointestinal tract by bacterial fermentation of harmful substances, resulting in nausea, vomiting and other uncomfortable symptoms of the baby ; 6, developmental delay: if long-term without effective treatment, malabsorption of nutrients can affect the normal growth and development, resulting in delayed development, and may even appear rickets, anemia and other diseases. In addition, babies with diarrhea, abdominal pain, nausea and vomiting and other uncomfortable symptoms can usually be accompanied by varying degrees of crying, restlessness and other performance, serious lactose intolerance may also appear allergies, dizziness, fever and other symptoms. Prolonged diarrhea may also lead to dehydration, dry mouth, dry skin, sunken eyes and other symptoms, requiring prompt medical attention. Lactose intolerance cannot be determined by symptoms alone, but needs to be diagnosed through tests such as stool routine, stool acidity test and the performance of lactose-free milk products after changing.