Prior studies related to skin aging have been focused primarily on the dermal changes such as reduction of the extracellular matrix, but aged epidermis develops an abnormality in permeability barrier homeostasis, leading to xerosis, pruritus, and abnormal susceptibility to exogenous agents. A global reduction in stratum corneum (SC) lipids, especially cholesterol, impaired SC acidification, decreased SC hydration, abnormal epidermal Hyaluronan (HA) metabolism, and oxidative stress are the molecular basis for the epidermal changes of aged skin. Developing technologies that enhance skin barrier function is an important part of the development of anti-aging cosmetics/cosmeceuticals. Hydroxy acids which are frequently used as the anti-aging cosmeceutical ingredients can enhance lamellar body secretion, ceramide biosynthesis, and HA synthesis by stimulation of epidermal Ca2+ gradient loss. Among the antioxidants, niacinamide is demonstrated to stimulate keratinocytes differentiation and ceramide synthesis and improve the SC moisture content. Among the growth factors, epidermal growth factor (EGF) upregulates epidermal HA synthesis, but it’s molecular sized is too large for skin penetration. As a vehicle for the anti-aging cosmetics/cosmeceuticals, physiologic lipid mixture (equimolar ratio of ceramides, cholesterol, and fatty acid or cholesterol dominant) with acidic pH can accelerate barrier recovery in aged skin. 11β-Hydroxysteroid dehydrogenase inhibitor and PPAR and LXR activators can be the promising anti-aging barrier enhancing strategies.
