Gluten is a protein found in wheat, rye, barley, triticale and oats. In some people, eating or drinking anything containing gluten can cause different types of undesirable reactions. The most extreme of these is the auto-immune condition known as celiac disease. Some other types of reactions are known as non-celiac gluten sensitivity, gluten sensitivity, or gluten intolerance. Gluten sensitivity is different from wheat allergy.
People with celiac disease and gluten sensitivity show improvement when they follow a gluten-free diet.