Crohn's disease is an inflammatory bowel disease in which inflammation injures the intestines. It is a long-term (chronic) condition. Crohn's disease typically begins between ages 15 and 40.
No one knows for sure what triggers the initial intestinal inflammation at the start of Crohn's disease. A viral or bacterial infection may start the process by activating the immune system. The body's immune system stays active and creates inflammation even after the infection goes away.
Certain genes passed on from parent to child may increase risk of developing Crohn's disease if the right trigger occurs.
Once Crohn's disease begins, it can cause lifelong symptoms that come and go. The inside lining and deeper layers of the intestine wall become inflamed. The lining of the intestine becomes irritated. It can thicken or wear away in spots. This creates ulcers, cracks and fissures. Inflammation can allow an abscess (a pocket of pus) to develop.
A common complication of Crohn's disease is called a fistula. A fistula is an abnormal connection between organs in the digestive tract, usually between one part of the intestine and another. A fistula can be created after inflammation becomes severe.
The section of the small intestine called the ileum is especially prone to damage from Crohn's disease. The ileum is located in the right lower abdomen. However, ulcers and inflammation can occur in all areas of the digestive tract, from the mouth to the rectum.
A few other parts of the body, such as the eyes and joints, also can be affected by Crohn's disease.