Allergy refers to an inappropriate or exaggerated immune response to an otherwise benign substance, known as an allergen. This adverse reaction occurs when the immune system mistakenly identifies a substance—which may be pollen, certain foods, metals, or dust mites—as a threat. The physiological cascade involves the production of specific antibodies and the release of inflammatory mediators, which can trigger symptoms ranging from localized skin rashes and sneezing to severe systemic reactions. While allergies can manifest in various forms, advanced manifestations may lead to rapid circulatory collapse, requiring immediate medical intervention. The study and management of allergic disease involve identifying specific triggers and utilizing therapeutic agents to modulate the immune system's overreaction.