Gluten is a general name for the proteins found in wheat, rye, barley and triticale. Gluten helps foods maintain their shape, acting as a glue that holds food together and is also responsible for foaming action in bakery products. Gluten can be found in many types of foods, even ones that would not be expected.
Gluten is not harmful to all people, but to those who are intolerant to it, a condition known as coeliac disease.
Celiac disease is a serious autoimmune disorder that can occur in genetically predisposed people where the ingestion of gluten leads to damage in the small intestine. It is estimated to affect 1% of the people worldwide.
Currently, the only treatment for celiac disease is lifelong adherence to a strict gluten-free diet. People living gluten-free must avoid foods with wheat, rye and barley, such as bread and beer. Ingesting small amounts of gluten, like crumbs from a cutting board or toaster, can trigger small intestine damage.
Information retrieved from: https://celiac.org