Use Vitamin C Serum? Here's the One Thing You Need To Know

Vitamin C is the ultimate tease. Every dermatologist, esthetician, and beauty editor will tell you it's a must-have in your skin care regimen. For good reason: The superpowered antioxidant is shown to even tone, help smooth fine lines, and fight free radicals.

But, as an ingredient, it's also highly unstable and finicky. It loses efficacy with just the slightest provocation by pretty basic stuff: air, light, and just generally over time. For example, It needs to be packaged in a dark glass or an opaque bottle so light can't hit it. You also shouldn't keep it in an area that gets too hot, as elevated temperatures can break it down. Finally, air can cause it to oxidize—you'll notice this is happening when the liquid starts changing its color to brown—so it's best packaged in an airtight pump or tube.

Then you get into the formulation question: Since there's little regulation around skin care products, brands can market a serum as an antioxidant-fueled savior, without actually formulating the ingredient at effective levels. Meaning: Brands put enough in so they can say it's in there, even if it's not doing anything substantial. Vitamin C works best when formulated at about 10 to 20%, but unless a brand explicitly states the percentages, it's impossible to know. (Side note: Many people think you can just look and see where an active falls on the ingredient list, but that's an inaccurate reading. Some actives work best at smaller percentages and therefore will be at the bottom.)

So even if you correctly care for your precious little tonic, there's a chance it wasn't doing anything from the start. Truly, all things considered, it's nearly a beauty miracle that anyone can find an option that works.

And I'd hate to complicate matters more, but here's the next layer you need to know. However, this tip can actually make your product more effective, not less. It involves a little biology and chemistry lesson.

"There are two categories of antioxidants: water-soluble or oil-soluble," says herbalist and board-certified dermatologist Steven Wang, M.D. "And the point of antioxidants is to neutralize free radicals, both in oil phase and water phase of our bodies. Our body needs both oil- and water-soluble antioxidants."

Vitamin C, you'll see it as ascorbic or l-ascorbic acid, is a water-soluble antioxidant, so it activates when in water. Our cells are made of 70 percent water, so when vitamin C is applied to the skin, it penetrates the skin cells, activates in the water, and starts fighting off free-radicals.

But if you also remember from biology class, cells have lipid (or oil) barriers. Naturally, vitamin C is not oil-soluble. But some antioxidants are: vitamin E being the most prevalent. (The others options are vitamins A, D, and K.) These also fight free-radicals and damage, but in parts of the body that are made of fat and oil.

So when you are looking for a vitamin C product, your best bet is to find one that is also formulated with an oil-soluble agent. Not only will the product be able to work in more parts of the skin cell, but it becomes a "the whole is greater than the sum of its parts," situation.

"The two work together and have something of a synergistic effect," says Wang. "Making each better and more effective." It functions like this: As each antioxidant works in its respective area, they actually start working together to "recharge" each other, according to Wang. After neutralizing free radicals, the antioxidants need a boost, which each readily provides the other. (I liken it to the antioxidants are giving each other pep talks.)

The more you know, no?

So at this point, you might be thinking, what about vitamin C formulated in oils, rather than water-based serums? If you are ready to round up your vitamin C oils and toss them in the trash, not so fast. I asked Wang about how those options might work: And to make matters more complicated, there are forms of vitamin C that are oil-soluble, tetrahexyldecyl ascorbate and ascorbyl palmitate being the most common. These are more stable versions of ascorbic and l-ascorbic acid, which is why you will often seem them in tinctures with droppers, as they don't break down from air as quickly. And many of these formulations work quite well, however, generally these two antioxidants tend not to be as powerful as ascorbic and l-ascorbic.

Confused yet? Not sure where to find a product that works? We've rounded up a few of our favorites.