Allergies represent a widespread health concern, affecting millions globally with symptoms ranging from mild discomfort to severe, life-threatening reactions. Understanding how the human body reacts unexpectedly to normally harmless substances has been a long journey, marked by critical observations and groundbreaking discoveries. This journey has shaped our current understanding of allergies.
The Naming of Allergy
The term “allergy” was coined in 1906 by Austrian pediatrician Clemens von Pirquet. He observed that some of his patients developed altered responses, or “changed reactivity,” to substances like horse serum used in diphtheria antitoxin or to smallpox vaccinations. These reactions indicated a heightened or different immune response upon re-exposure, unrelated to the original disease.
Pirquet derived “allergy” from the Greek words “allos” (“other”) and “ergon” (“reaction” or “work”), describing a “different reaction.” His concept unified various seemingly unrelated conditions, such as asthma, hay fever, and eczema, under a single framework of altered reactivity. While Pirquet’s contribution was primarily conceptualizing and naming this phenomenon, his work laid a foundational understanding that the immune system, traditionally seen as protective, could also cause harm.
Early Insights into Hypersensitivity
Before Pirquet introduced “allergy,” scientists had already observed adverse reactions that hinted at hypersensitivity. A notable discovery was anaphylaxis, identified in 1902 by French physiologists Charles Richet and Paul Portier. They were researching the toxicity of marine animal venoms and observed unexpected, severe reactions in dogs upon a second, smaller exposure to the venom.
Instead of developing immunity, the dogs exhibited a life-threatening, opposite effect, which Richet and Portier named “anaphylaxis,” meaning “against protection.” This phenomenon demonstrated that an immune response could be detrimental, even fatal, challenging the prevailing view that immune reactions were solely protective. Richet received the Nobel Prize in Physiology or Medicine in 1913 for this discovery.
Broadening the Definition
The understanding of allergy evolved significantly, moving from a broad concept of altered reactivity to a detailed scientific understanding of specific immune mechanisms. A major advancement came with the discovery of Immunoglobulin E (IgE) in the late 1960s by independent research teams. This specific antibody was identified as the primary mediator of immediate hypersensitivity reactions, linking allergens to the release of inflammatory chemicals.
IgE antibodies attach to the surface of mast cells, which are immune cells. Upon re-exposure to an allergen, the allergen binds to IgE on the mast cell surface, triggering the mast cell to release mediators such as histamine. These mediators cause the characteristic symptoms of allergic reactions, including swelling, muscle contraction, and increased mucus production. The identification of IgE and the role of mast cells provided a concrete biological basis for allergic reactions, explaining the rapid onset of symptoms observed in conditions such as food allergies, seasonal allergies, and drug allergies. This understanding has deepened, allowing for classification of allergy types and development of targeted diagnostic and therapeutic approaches.