So when you apply hyaluronic acid topically, “it draws water into the stratum corneum, the top layer of the skin. It gives an immediate improvement in the way the skin looks—less ashy, dry, dull,” says holistic dermatologist Cybele Fishman, M.D. And since it’s attracting so much water to the area, you’ll also see a fuller and more lush appearance. It makes sense why it’s often formulated into lip products, no?
Now, if you want to get into specifics, there are actually different molecular weights of hyaluronic acid. (This is important because things with lower molecular weights can shimmy down deeper than those that are larger.) Cosmetic chemists often use different varieties and weights depending on the intended purpose. For our lip balm we used sodium hyaluronate. This is the sodium salt of hyaluronic acid, which has a lower molecular weight and therefore can reach deep down into the skin barrier, providing a more lasting and meaningful hydration.
And as is the case with any humectant, it should be formulated right alongside emollients and occlusives. Otherwise, humectants can have the unintended consequence of making your lips drier, as they can trigger transepidermal water loss once they start to lose binding of the water they once attracted. Read: Don’t just apply your HA serum to the area and call it a day. You either need to top it with a balm—or just find one with the ingredient already infused into it.
Source: https://www.mindbodygreen.com/articles/how-hyaluronic-acid-can-improve-your-skin-and-lips