But what makes hyaluronic acid so good at moisturising is the fact that it can hold up to 1,000 times its weight in water. Think of it like a soaked sponge that sits under the surface of the epidermis, and steadily drip-feeds skin with moisture throughout the day. As a result, lines look smoother because skin is plumper and dry patches vanish. But because it's a large molecule, it won't penetrate to the deepest layers, so that's where hyaluronic acid fillers , which are made of synthesised HA derived from sodium hyaluronate, come in.