<p>Gluten is a common allergen found in foods, yet do you know what exactly it is? Here&#39;s a look at gluten chemistry and the foods most likely to contain gluten.</p><h3>What Is Gluten?</h3>Gluten is a protein found exclusively in certain grasses (genus <em>Triticum</em>). It is a composite of two proteins, gliadin and a glutenin, bound to starch in the seeds of wheat and related grains.<h3>Gliadin and Glutenin</h3>Gliadin molecules mainly are <a href="https://www.thoughtco.com/definition-of-monomer-605375" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">monomers</a>, while glutenin molecules typically exist as large <a href="https://www.thoughtco.com/definition-of-polymer-605912" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">polymers</a>.<h3>What Does Gluten Do in Plants?</h3>Flowering plants, including grains, store proteins in their seeds to nourish plants when the seeds germinate. Gliadin, glutenin, and other prolamin proteins essentially are the building blocks used by the seeds as they sprout into plants.<h3>What Foods Contain Gluten?</h3>Grains that contain gluten include wheat, rye, barley, and spelt. Flakes and flour made from these grains contain gluten. However, gluten is added to many other foods, usually to add protein content, impart a chewy texture, or as a thickening or stabilizing agent. Foods that contain gluten include bread, grain products, imitation meats, beer, soy sauce, ketchup, ice cream, and pet foods. It is commonly found in cosmetics, skin products, and hair products.<h3>Gluten and Bread</h3>Gluten in flour is used to make bread. When the bread dough is kneaded, the glutenin molecules cross-link the gliadin molecules, forming a fibrous network that traps carbon dioxide bubbles produced by yeast or a leavening agent, such as baking soda or baking powder. The trapped bubbles make the bread rise. When bread is baked, the starch and gluten are coagulated, locking the baked goods into shape. Gluten binds water molecules in baked bread, which may be a factor in causing it to go stale over time.<h3>Rice and Corn</h3>Rice and corn contain prolamin proteins to support growth of seedlings, but they don&#39;t contain gluten! Gluten is a protein specific to wheat and other grasses in its family. Some people have chemical sensitivities to the proteins in rice or corn, but these are reactions to different molecules.<h3>What Causes a Gluten Allergy?</h3>An allergic reaction to gluten is celiac disease. It&#39;s estimated between 0.5% and 1% of people in the United States are allergic to gluten and that this frequency applies to other wheat-eating countries as well. The allergy is linked to an excessive immune response to partially digested gliadin.