Clinical studies of anti-IL-5 and/or anti-IL-5Rα biologics in severe eosinophilic asthma, chronic rhinosinusitis with nasal polyps, eosinophilic granulomatosis with polyangiitis, hypereosinophilic syndromes, and other eosinophilic diseases have improved outcomes, underscoring that disease activity often depends on IL-5-driven eosinophil activation despite disease-specific IL-5-independent signals. This evidence concerns the gene IL5RA and eosinophil disorder.