ATOPIC DERMATITIS: SKIN BARRIER DYSFUNCTION, TH2-DOMINANT IMMUNOPATHOGENESIS, DIAGNOSTIC CRITERIA, AND TARGETED BIOLOGIC AND SMALL-MOLECULE THERAPY

Background: Atopic dermatitis (AD) is the most prevalent chronic inflammatory skin disease, affecting 15–20% of children and 1–10% of adults worldwide—representing more than 230 million affected individuals globally. Characterized by intense pruritus, skin barrier dysfunction, and relapsing eczematous lesions, AD profoundly impairs quality of life and is the leading cause of years lived with disability (YLD) among skin diseases. Recent decades have established AD as a complex immunological disorder driven by type 2 helper T-cell (Th2) skewing, IL-4/IL-13 cytokine axis overactivation, and filaggrin-mediated skin barrier defects, fundamentally transforming therapeutic targeting.