Short answer? Apply your vitamin C first, then pat on your HA. Vitamin C (especially L-ascorbic acid) is notoriously unstable—it loses potency when it’s exposed to air, light, and water—which is why you want to apply it on clean, dry skin right after washing. You’ll also want to let it dry completely, as piling on products right after could potentially deactivate the vitamin C.
You don’t need to be as precious with hyaluronic acid. Yes, applying on damp skin will make it easier for the humectant to pull in water, but it can also draw in that moisture from the surrounding environment, too. Let’s not forget: Hyaluronic acid can hold up to 1,000 times its weight in water, and you don’t necessarily have to provide that water yourself. “That way, you don’t need to worry that HA needs to go directly onto damp skin,” says board-certified dermatologist Ife J. Rodney, M.D., FAAD, founding director of Eternal Dermatology + Aesthetics.
So you can apply your vitamin C first, let it dry completely, then apply your hyaluronic acid. Just remember to top everything off with a moisturizer—you still want to seal in the HA to lock in the hydration.
Or, if you do want to apply your HA on damp skin to maximize its benefits, board-certified dermatologist Ava Shamban, M.D., founder of SkinFive and The Box by Dr. Ava, still recommends applying your vitamin C serum and letting it dry completely. “The highly reactive nature and low pH of vitamin C in serum form will usually allow it to penetrate the cleansed, dry skin quickly,” she says. After it dries, apply a water-based hydrating toner or essence (here are our favorites), then pat your hyaluronic acid serum onto the freshly misted skin. Again, follow up with a moisturizer to lock in the hydration.