Celiac disease is an autoimmune disease. If you have celiac disease, your body cannot tolerate gluten, a protein found in wheat, barley, rye and sometimes oats. If you eat gluten, your immune system responds by damaging or destroying the lining of the small intestine in the digestive tract (called villi). Without villi, your body cannot absorb nutrients from food into the bloodstream.
Even short-term exposure to gluten can cause serious symptoms if you have celiac disease.