There are several causes for diarrhea. The most common causes are an infection of the stomach or intestines, irritable bowel syndrome, food allergies, medication (such as antibiotics), stress or chronic diseases like Crohn's disease or ulcerative colitis. You can also get diarrhea if you are constipated.
Gastrointestinal infections can be caused by viruses, bacteria and parasites. You can contract these infections everywhere. Diarrhea is called 'chronic' if you have had diarrhea for at least six weeks. When no clear cause for the diarrhea is found, it is called 'unexplained'.