Crohn's disease is an inflammatory disease of the digestive system that affects children and adults. The cause of Crohn's disease is unknown, but a combination of genetic predisposition and environmental factors is suspected. Symptoms of Crohn's disease are usually mouth sores, fatigue, diarrhea, abdominal pain, weight loss, and fever. Patients may also have symptoms outside the digestive system: skin rash, joint pain, red eyes, and liver problems.