Eating onions and having diarrhea may be caused by allergic gastroenteritis and other digestive diseases. 1. Allergic gastroenteritis: onions belong to a kind of allergenic food, easy to cause the digestive system tissue metamorphic reaction, resulting in the stomach and intestines of these organs and tissues of the mucous membrane by the adverse stimuli caused by the decomposition and absorption of the obstacles to the body of a large amount of water and nutrients can not be absorbed through the intestinal tract, and through the excretory system out, causing diarrhea. 2. Other digestive diseases: such as gastric ulcer, chronic gastritis, chronic enteritis, etc., these digestive diseases can also cause gastrointestinal adverse reactions, resulting in gastrointestinal tract lesion tissue stimulation and induced contraction spasm and peristalsis enhancement, resulting in an increase in the number of bowel movements, and even diarrhea. It is recommended that patients go to regular hospitals to receive examination to clarify the cause, and treatment according to the results of the examination.