A food allergy is a specific adverse reaction involving the immune system, triggered by otherwise harmless food proteins. For centuries, people observed that certain foods caused illness, but they could not distinguish between a true immune response and simple food intolerance or poisoning. Identifying food allergy as a unique immunological disease required landmark discoveries in the nature of immune hypersensitivity and the identification of the specific antibody responsible.
Ancient Awareness of Adverse Food Reactions
Long before the mechanisms of immunology were understood, historical figures noted that certain foods could be toxic to specific individuals. The Greek physician Hippocrates, around 400 BC, is often credited with recognizing that foods could cause adverse symptoms like digestive issues and hives. He documented observations of patients who reacted negatively to specific foods, such as milk.
The challenge for pre-scientific medicine was the lack of tools to determine the cause of the reaction. Since there was no concept of an immune system, adverse food reactions were often mistakenly grouped with general food poisoning or other digestive intolerances. Early writings focused on observing the symptoms and identifying the culprit food, but the difference between an immediate immune response and a simple digestive upset remained unknown.
The Dawn of Immunological Hypersensitivity
The first significant step toward understanding the mechanism behind severe food reactions occurred in the early 20th century. In 1902, French physiologists Charles Richet and Paul Portier were studying sea anemone toxins on dogs, attempting to induce protective immunity (phylaxis). They discovered that a second, small injection of the toxin, given weeks later, caused a sudden, severe, and often fatal collapse—the opposite of protection.
Richet and Portier coined the term “anaphylaxis,” meaning “against protection,” to describe this exaggerated state of sensitization. This work established the concept that the immune system, once exposed to a foreign substance, could become sensitized and react violently upon re-exposure. This provided the conceptual foundation for understanding the most severe forms of food allergy.
Coining the Term Allergy and Early Food Connections
The next significant development was the creation of a term to classify this altered state of reactivity more broadly. In 1906, Austrian pediatrician Clemens von Pirquet introduced the term “allergy,” derived from the Greek words allos (other) and ergon (reaction). He used the term to describe any unusual or exaggerated reaction to a foreign substance, such as those seen after smallpox vaccination or injections of horse serum.
His concept proposed that the immune system could cause harm, not just protection, applying this “altered reactivity” to a wide array of conditions. Physicians soon applied the new term to chronic conditions like asthma, hay fever, and adverse reactions linked to food intake. This conceptual shift separated food allergy from simple poisoning, classifying it as a form of abnormal biological response. However, the precise biological component responsible for the immediate hypersensitivity reaction remained a mystery for several decades.
The Discovery of IgE and Modern Confirmation
The definitive scientific confirmation of the immediate food allergy mechanism occurred in the late 1960s with the discovery of Immunoglobulin E (IgE). Researchers were previously aware of an unknown serum factor, called “reagin,” that mediated allergic reactions, but they could not isolate it. Two independent research teams simultaneously identified this specific antibody.
In the United States, Kimishige and Teruko Ishizaka successfully isolated and identified a new class of immunoglobulin, calling it gamma E-globulin. Simultaneously in Sweden, S.G.O. Johansson and Hans Bennich identified the same molecule while studying a patient with a rare form of myeloma. The two groups confirmed their findings, and the World Health Organization officially named the specific antibody Immunoglobulin E (IgE) in 1968.
The discovery of IgE provided the long-sought biological marker linking harmless food proteins to the severe symptoms of immediate hypersensitivity. This allowed for the development of modern diagnostic tools, such as the Radio-Allergo Sorbent Test (RAST), which measures allergen-specific IgE antibodies in the blood. IgE identification marked the point where food allergy transitioned from a clinical observation to a verifiable immunological disease.