Gluten (from Latin gluten, "glue") is a protein composite found in wheat and related grains, including barley and rye. Gluten gives elasticity to dough, helping it rise and keep its shape and often gives the final product a chewy texture. Gluten is used in cosmetics, hair products, and other dermatological preparations.
In individuals with coeliac disease (spelled "celiac" in American English), consumption of gluten causes adverse health issues ranging from abdominal bloating, gas, diarrhea and vomiting to migraine headaches and joint pain. Coeliac disease is an autoimmune disorder that affects the digestive process of the small intestine. In 2009 research showed between 0.5 and 1.0 percent of people in the US and UK are sensitive to gluten due to coeliac disease. It probably occurs with comparable frequency among all wheat-eating populations in the world. Coeliac disease has no cure but is manageable with a gluten-free diet.
Non-coeliac gluten sensitivity (sometimes known as gluten intolerance) is a condition thought to arise as a result of an immunological response to gluten that differs in nature to the immune response characteristic of coeliac disease. However, there is no current scientific consensus that this is a genuine pathological condition and the mechanism by which this could occur is unknown. Frequently, symptoms could arise in individuals as a result of undiagnosed coeliac disease or due to a reaction to other components of wheat, such as short-chain, fermentable carbohydrates called FODMAPs.
People can also experience adverse effects of wheat as result of a wheat allergy. As with most allergies, a wheat allergy causes the immune system to abnormally respond to a component of wheat that it treats as a threatening foreign body. This immune response is often time-limited and does not cause lasting harm to body tissues. Wheat allergy and coeliac disease are different disorders.