Loricrin is a major structural protein component of the cornified envelope (CE), a specialized macromolecular protein-lipid complex that replaces the plasma membrane during terminal keratinocyte differentiation 1. Located primarily in the granular layer of human epidermis 2, loricrin becomes incorporated into the CE of stratum corneum cells where it is cross-linked with other proteins to form an insoluble, mechanically resilient barrier 2. This barrier provides desiccation tolerance and cytoprotection critical for skin function 3. Loricrin expression is tightly regulated by inflammatory cytokines and transcription factors; IL-4, IL-13, IL-17A, and IL-22 potently inhibit loricrin expression via STAT3/STAT6 pathways, while aryl hydrocarbon receptor (AHR) and NRF2 agonists upregulate it 4. Loricrin downregulation is associated with barrier dysfunction in atopic dermatitis and psoriasis 5, with periodontitis patients showing the most severe downregulation (-6.89x) 5. Mutations in the loricrin gene cause Vohwinkel syndrome and progressive symmetric erythrokeratoderma, characterized by abnormal protein localization and thinner CEs 6. Despite loricrin's structural significance, knockout mice demonstrate it is dispensable for barrier permeability but affects broader skin homeostasis 3. Therapeutically, abrocitinib enhances loricrin expression in atopic dermatitis lesional skin more effectively than dupilumab 7.