Crohn's disease is a long-lasting disease. It causes inflammation — swelling and irritation — in your digestive tract. It can affect any part of the tract, from your mouth to your anus. Most often, it affects your small intestine and the start of your large intestine. Researchers think an autoimmune reaction may be one cause. That means your immune system attacks healthy cells by mistake. Genes may also play a role. Crohn's can run in families. The most common symptoms are diarrhea, belly pain and cramping, and weight loss. Other symptoms can include fatigue, fever, joint pain, nausea, and skin changes. Stress and certain foods, like carbonated drinks or high-fiber foods, do not cause the disease. But they can make symptoms worse for some people. Over time, Crohn's can cause other problems. These include intestinal blockages, fistulas — abnormal tunnels between body tissues — abscesses, and poor nutrition. Talk to your care team about what to watch for and how to protect your health.