Normal stool test but diarrhea can be caused by many reasons, such as lactose intolerance, milk protein allergy, irritable bowel syndrome, etc. 1. Lactose intolerance: the body lacks the enzyme lactase to digest the lactose present in milk, resulting in metabolic disorders, mainly manifested as bloating, abdominal discomfort and diarrhea after eating milk. 2. Milk protein allergy: an abnormal or overly strong immune response caused by the large molecular proteins in milk. 3. Irritable Bowel Syndrome (IBS): a functional gastrointestinal disorder without organic lesions, which may be related to mental factors, abnormal intestinal motor-sensory function, autonomic dysfunction and so on. In addition, these symptoms may be caused by fat malabsorption, congenital malformations (e.g., pseudo-obstruction, congenital megacolon), neuroendocrine problems (vasoactive peptide tumors, multiple endocrine tumors, etc.), and so on. Normal stool test but diarrhea may also have other causes, it is recommended to consult a doctor in time, under the guidance of the doctor to carry out targeted treatment and therapy, to avoid adverse consequences.