Diarrhea is a symptom -- it is not a disease. It is defined as loose, watery stools that occur more than three times in one day. Some of the things that can cause diarrhea include infections, food intolerance, reactions to medicine, intestinal diseases, and functional bowel disorders. While most people with diarrhea get better on their own, diarrhea can be serious for babies. There are a number of situations in which a person with diarrhea should see a healthcare provider. For example, you should see a healthcare provider if diarrhea is accompanied by signs of dehydration, blood in the stool, or a fever of 102 degrees Fahrenheit or higher, among other symptoms.