Celiac disease is an inherited disorder that damages the small intestine and interferes with nutrient absorption. People with this condition have an intolerance for gluten, which is found in wheat, rye, and barley. Symptoms of the disease may include diarrhea, abdominal pain (or stomach pain), and irritability. The disorder is typically treated by eliminating all gluten from the diet, and people with celiac disease must follow this gluten-free diet for the rest of their lives.