Diarrhea once a day may be caused by physiological reasons, such as nervousness, etc., may also be caused by pathological reasons, such as irritable bowel syndrome, enteritis, etc.. 1. Physiological reasons: such as nervousness, nervousness stimulates gastrointestinal peristalsis to accelerate, diarrhea once a day. 2. Pathologic causes: (1) irritable bowel syndrome: the stomach and intestines are easily provoked, for example, slight temperature changes can also stimulate the stomach and intestines, causing diarrhea once a day. (2) enteritis: bacterial infection of the intestinal tract triggers inflammation and edema, stimulating the peristalsis of the intestinal tract to accelerate, diarrhea once a day will occur. Diarrhea once a day may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.