Celiac disease is a digestive disorder characterized by intolerance to dietary gluten, which is a protein found in wheat, rye, and barley. Consumption of gluten leads to abnormal changes of the mucous membrane (mucosa) of the small intestine, impairing its ability to properly absorb fats and additional nutrients during digestion (intestinal malabsorption). Symptom onset may occur during childhood or adulthood. In affected children, such symptoms may include diarrhea, vomiting, weight loss or lack of weight gain, painful abdominal bloating, irritability, and/or other abnormalities. Affected adults may have diarrhea or constipation; abdominal cramping and bloating; abnormally bulky, pale, frothy stools that contain increased levels of fat (steatorrhea); weight loss; anemia; muscle cramping; bone pain; exhaustion (lassitude); and/or other symptoms and findings. Although the exact cause of celiac disease is unknown, genetic, immunologic, and environmental factors are thought to play some role.