Hyaluronic Acid

Hyaluronic acid is a humectant: it draws water toward the surface of the skin and holds it there, so a fresh layer leaves the face smooth and cushioned to the touch. Press it onto skin that is still damp, then seal it with a moisturizer, so the water it gathers stays put instead of drifting off into dry indoor air. In a face wash it gives the rinse a softer, less tight feel; in a serum it is the whole point of a hydrating step.