Fc epsilon RI alpha (FcεRIα) is the α-chain of the high-affinity IgE receptor (FcεRI), a critical mediator of type I hypersensitivity. As a transmembrane glycoprotein in the immunoglobulin superfamily, its extracellular domain specifically binds the Fc region of IgE. Mainly expressed on mast cells and basophils, FcεRIα cross-linking (by IgE-allergen complexes) triggers cell degranulation, releasing histamine and proinflammatory mediators—driving allergies, asthma, and anaphylaxis. It also participates in immune surveillance. Owing to its central role in allergic responses, FcεRIα is a key therapeutic target for anti-allergy agents.