EPX, also known as eosinophil peroxidase, is a cationic heme‑containing peroxidase enzyme that is predominantly stored in the specific granules of eosinophilic granulocytes. Encoded by the EPX gene located on human chromosome 17q13.1, the enzyme is synthesized as a single‑chain precursor that undergoes proteolytic cleavage to form a heavy and a light chain, which remain covalently associated in the mature protein. Upon eosinophil activation by immunological or inflammatory stimuli, EPX is secreted into the extracellular milieu where it catalyzes the hydrogen peroxide‑dependent oxidation of halides (bromide, chloride) and thiocyanate to generate potent cytotoxic oxidants, such as hypobromous acid and hypothiocyanous acid. These reactive species are essential for the eosinophil's effector function against helminthic parasites and certain bacteria, but they also exert profound pro‑inflammatory and tissue‑damaging effects when released inappropriately. Indeed, elevated EPX levels and activity have been implicated in the pathogenesis of allergic asthma, atopic dermatitis, and other eosinophilic disorders, making the enzyme not only a useful diagnostic biomarker but also an emerging therapeutic target for modulating eosinophil‑driven inflammation.