Crohn's disease, also known as ileitis or enteritis, is a type of inflammatory bowel disease that causes patches of inflammation along the digestive tract -- most commonly near the end of the small intestine and in the colon. In a person with Crohn's disease, the inflammation frequently affects more than one layer of the wall of the digestive tract, and it can cause the intestines to empty more frequently -- resulting in diarrhea. While the disease can affect people of all ages, it is usually diagnosed before the age of 30. It cannot be cured in most people, so it usually requires lifelong treatment.