What is Crohn’s disease? Crohn’s disease is a chronic inflammation of the gastrointestinal tract and one form of inflammatory bowel disease. In Crohn’s disease, the body’s immune system mistakenly attacks healthy tissues in response to food or infection in the digestive tract. The disease can affect any part of the gastrointestinal tract, but it most commonly affects the lower portion of the small intestine (the ileum). Other areas affected include the mouth, esophagus, stomach, small intestine, large intestine, and rectum. Symptoms often have an insidious onset and happen in intermittent bouts. The frequency and intensity of symptoms steadily progress over time. Delay in diagnosis is common due to the diverse pattern of symptoms. Classic symptoms of Crohn’s disease include abdominal pain and swelling and frequent episodes of diarrhea. Crohn’s disease can seriously affect a person’s ability to participate in normal daily activities and can lead to serious complications including malnutrition and blockage in the intestines. Children who have Crohn’s disease may experience growth problems. The exact cause of Crohn’s disease is not known, but researchers believe it may be an autoimmune disorder that tends to run in families. Crohn’s disease can affect all age groups but especially young adults ages 15 to 35. Chronic inflammation of the gastrointestinal tract due to Crohn’s disease can lead to serious or life-threatening complications, such as nutritional deficiencies, gastrointestinal bleeding, anemia, and bowel obstruction. Seek prompt medical care if you have symptoms of Crohn’s disease, such as abdominal pain and frequent diarrhea. Seek immediate medical care (call 911) if you, or someone you are with, have severe bleeding from the rectum, severe and constant abdominal pain, or an unusual change in alertness.