Being allergic to barley while tolerating wheat is possible, despite the grains being botanically related. A true food allergy is an IgE-mediated immune response that targets specific protein structures within the food. While barley and wheat share some protein families, they also contain distinct proteins. If the immune system has been sensitized only to the unique allergenic proteins found in barley, the individual can safely consume wheat without an allergic episode.
Distinguishing Allergy from Gluten Sensitivity
To understand grain reactions, it is helpful to clarify the differences between three distinct conditions. An IgE-mediated food allergy to a grain is an immediate hypersensitivity reaction involving Immunoglobulin E antibodies. Symptoms can range from hives and swelling to life-threatening anaphylaxis, occurring rapidly after ingestion.
This type of allergy is fundamentally different from Celiac Disease, which is a genetic autoimmune condition. In Celiac Disease, the ingestion of gluten—a protein found in wheat, barley, and rye—triggers a T-cell-mediated immune response that damages the lining of the small intestine. Celiac reactions are not immediate like an IgE allergy, and they require complete, lifelong gluten avoidance.
A third condition is Non-Celiac Gluten Sensitivity (NCGS), sometimes called gluten intolerance. NCGS is diagnosed when Celiac Disease and a wheat allergy have been ruled out, but symptoms like bloating, abdominal pain, or fatigue occur after consuming gluten-containing grains. The underlying biological mechanism for NCGS is not yet fully defined. It does not involve the autoimmune damage seen in Celiac Disease or the IgE antibody reaction of a true allergy.
The Science Behind Specific Grain Sensitization
Both wheat and barley belong to the grass family and contain gluten proteins, which are primarily storage proteins known as prolamins. The prolamin in barley is called hordein, while the prolamins in wheat are gliadins and glutenins. These proteins are composed of smaller structures, and it is the precise structure of these allergenic protein fragments, known as epitopes, that determines the immune response.
Although related, the specific hordein proteins in barley possess unique amino acid sequences that differ structurally from the gliadins and glutenins in wheat. An individual with a specific barley allergy has manufactured IgE antibodies only against these unique barley epitopes. This is known as specific sensitization, meaning the immune system targets only the barley proteins and ignores the distinct proteins found in wheat.
The potential for cross-reactivity does exist because barley and wheat share some structural similarities in their proteins. For instance, a barley protein called gamma hordein has been shown to cross-react with omega-5 gliadin, a major allergen in wheat. However, cross-reactivity is not guaranteed, and many individuals remain clinically sensitized to only one grain. The immune system’s recognition of shared versus unique epitopes is the scientific basis for why someone can react severely to barley but safely eat wheat.
Identifying and Managing Grain Allergies
A differential diagnosis is necessary to confirm a specific barley allergy and rule out a reaction to wheat or other conditions. Diagnosis is typically performed by a medical professional, such as an allergist. The primary diagnostic tools are the skin prick test and a specific IgE blood test.
The skin prick test involves placing a small amount of purified barley and wheat extract onto the skin and lightly scratching the surface. A raised, red welt at the barley site, with no reaction at the wheat site, suggests a specific barley allergy. The specific IgE blood test measures the amount of IgE antibodies in the bloodstream directed against barley proteins, confirming the IgE-mediated response.
Management of a confirmed barley allergy centers on strict avoidance of the grain. Individuals must identify hidden sources of barley, which often include malt, malt flavoring, and beer. Since an IgE-mediated allergy can cause anaphylaxis, patients at risk are advised to carry an epinephrine auto-injector and have a written emergency action plan. If the medical diagnosis confirms tolerance to wheat, a person can continue to consume wheat products safely while avoiding all forms of barley.