FLG and Alzheimer disease: Epidermal barrier (third field/target area) disruption is a hallmark of AD and is mostly due to a combination of two factors: first, mutations or alterations in the genes encoding the structural-filament-associated protein filaggrin that binds to keratin fibres in epithelial cells [42], and, second, the overexpression of inflammatory cytokines, such as IL-13, which will further disrupt the epidermal layer and impair or dysregulate epidermal barrier function, leading to increased skin permeability [43,44].