We conducted a narrative synthesis of mechanistic, translational, and clinical evidence on Th2 pathways in atopic dermatitis (AD), prurigo nodularis, bullous pemphigoid, chronic spontaneous urticaria, and selected type I/IVb hypersensitivity reactions, with focused appraisal of trials targeting IL-4Rα, IL-13, and IL-31R. The gene discussed is IL4R; the disease is Alzheimer disease.