Because along with all the glowing reviews, there’s one important rider to mind: Vitamin C degrades and deactivates quickly. It’s a water-soluble vitamin, so it loses its potency as soon as it’s exposed to air, heat, light, and—you guessed it—water. As board-certified dermatologist Julia T. Hunter, M.D., founder of Wholistic Dermatology, puts it: “It starts oxidizing and losing its chemical power.”
That’s why a vitamin C serum has a relatively shorter shelf life than the other products in your repertoire. (When it starts to visibly oxidize in the bottle, resulting in a yellow-brown substance, it’s probably time to toss it.) All that said, you don’t want to introduce vitamin C to any more air and water droplets than you already have to (like, every time you open the bottle)—so why would you willingly pat it on moist skin?
The solution here is simple: Just make sure your face is completely dry before pumping out product. Most experts will recommend waiting 30 to 60 seconds between cleansing and massaging in vitamin C—and if you love a good hydrating toner or essence, perhaps skip the spritz or wait until it completely dries.
Now, if you’re a skin care aficionado, you may at this point be thinking, Hey what about all that advice about skin being more permeable when wet? To which we say, Wow you are correct and really know your skin care facts! Buteven if your skin is more permeable, what’s the difference if what you’re applying isn’t as effective? That’s why it is advisable to apply vitamin C on dry skin—and feel free to stick to damp for most of the rest.
Finally, and just as important, following your application you must wait for the product to dry itself. If you don’t give your skin adequate time to drink in the actives before slathering on a cream or lotion, you may mix the antioxidant with another ingredient that it doesn’t play well with; this, too, will make it less effective.