This hydrating serum strengthens the skin's moisture barrier in one drop. ""The skin barrier is the outer surface of the skin. It acts as a powerful shield to help protect against external aggressors. It works to keep the good stuff in and the bad stuff out. When your skin barrier's natural balance is compromised it can leave your skin more vulnerable and more sensitive."" - Dr. Annie Black, Lancome International Scientific Director. A strong skin moisture barrier helps lock in hydration and defend against external aggressors, including pollution, cold and dry weather. Formulated with 10% bifidus prebiotic, hyaluronic acid, and vitamin Cg, this hydrating serum helps improve the look of dull skin for visibly glowing skin.