IgE-mediated describes allergic reactions driven by immunoglobulin E — the antibody class behind immediate hypersensitivity. On first exposure to an allergen (peanut protein, pollen, bee venom), susceptible individuals produce IgE antibodies that arm mast cells and basophils; on re-exposure, the allergen cross-links those antibodies and the cells explosively release histamine, tryptase, and inflammatory mediators — hives, swelling, wheeze, and anaphylaxis within minutes. Skin-prick tests and specific-IgE blood tests detect this pathway, distinguishing true allergy from intolerance. Most food allergies — peanut, tree nut, milk, egg, shellfish — are IgE-mediated, which is why reactions are rapid, dose-independent, and potentially fatal: the immunology explains the urgency.