Vitamin C Is the Ultimate Skin Ingredient—Here's Why

While some skincare ingredients are shrouded in obscurity, others are much more familiar—one of the latter being vitamin C. It's so ubiquitous in brightening products, wrinkle-reducing eye creams, anti-aging serums, and other treatments that whether you're just dabbling in skincare or you're the friend everyone texts for advice, we're willing to bet you've heard of the powerful antioxidant. But if you have yet to incorporate a vitamin C product into your skin routine, allow us to convince you of the many reasons why you should.

Ahead, experts Ron Robinson, Anna Guanche, Jennifer Herrmann, and Renée Rouleau share all the need-to-know details about vitamin C, including its benefits and the most effective ways to use it.

Keep reading for the complete guide to the popular antioxidant ingredient.

What Is Vitamin C?

According to Robinson, vitamin C is an essential nutrient required for the growth and repair of tissues in all parts of the body, including the skin, but we cannot produce it on our own. The powerful antioxidant is found naturally in fruits and vegetables and commonly produced synthetically in skincare products, such as moisturizers, toners, and, most often, serums.

"It is important to note that vitamin C has both active and inactive forms," explains Guanche. "Depending on the skincare formulation, applying vitamin C can do absolutely nothing or can work as a powerful antioxidant." The first form of vitamin C worth mentioning is the pure form, L-ascorbic acid. Herrmann says this is the most biologically active and well-studied form of vitamin C, but there are also several vitamin C derivatives, such as sodium ascorbyl phosphate, ascorbyl palmitate, retinyl ascorbate, tetrahexyldecyl ascorbate, and magnesium ascorbyl phosphate.

"These derivatives are not pure vitamin C, rather they are combined with other ingredients, which might help to keep the vitamin C stable," Robinson adds. "So when these derivatives come in contact with the skin, they release the pure vitamin C onto the skin." For example, if a product contains 10 percent of one of these derivatives, it might only release 3 percent of pure vitamin C on the skin, he says. Herrmann adds that the variants mostly differ in their hydrophilicity (i.e. their ability to easily dissolve in water) and pH.

In some cases, as with Klairs' Freshly Juiced Vitamin Drop, other ingredients include extracts of other citrus fruits and flowers.

How It Works

To understand how vitamin C works, we first need to know how free radicals damage the skin. There are three types of free radicals, but Rouleau is mainly concerned with the reactive oxygen species (ROS). "We are exposed to ROS from the air we breathe (oxygen), cigarette smoke, UV sunlight, stress, and smog," she says. The effects of ROS are no joke: They damage the dermis of the skin and alter DNA, the moisture barrier, skin texture, color, and cell functioning.

To demonstrate the effects of ROS and oxidative stress to the naked eye—and to prove how vitamin C works to combat them—Rouleau devised a simple experiment involving an apple. She coated one end of a slice with a thin layer of vitamin C serum and left the other side completely untouched. Then, she waited for three hours. Here's what happened:

As you can see, the side of the apple that was coated with the vitamin C serum didn't oxidize at all. "This shows how topical vitamin C can prevent oxidation, and therefore, slow down the visible appearance of aging," Rouleau says.

Vitamin C is very reactive and easily loses its antioxidant properties when exposed to heat, light, air, and other chemicals. To prevent it from oxidizing and deactivating, use vitamin C products that come in air-tight, opaque packages and store them in a cool, dark environment. If your product has turned brown, Herrmann says it’s best to toss it and replace it with a new bottle, as this change in color indicates that the formula has oxidized and is no longer effective.

Benefits of Vitamin C for Skin

Vitamin C is an impressive skincare ingredient that is shown to be effective in the following areas:

• Protects against environmental stressors: As an antioxidant, one of vitamin C’s main functions is protecting the skin. "Normal cellular processes, as well as environmental insults like ultraviolet light and pollution, create free radicals in the skin," Herrmann explains. "Free radicals are inherently unstable molecules that damage cells, promoting skin dullness, wrinkles, and even cancers." Guanche adds, "Vitamin C is an antioxidant, which means that it can protect skin from damaging free radicals caused by UV exposure." By scavenging these free radicals, vitamin C protects the skin, keeping it healthy and improving visible signs of aging.
• Promotes collagen production: Vitamin C also plays an important role in collagen synthesis. "Collagen gives our skin support and structure, and as it degrades with age, we begin to notice wrinkles and lines," Herrmann explains. "Vitamin C is a necessary cofactor for building collagen bundles, without which this process halts."
• Lightens dark spots: Vitamin C is also helpful in lightening unwanted dark spots and post-inflammatory hyperpigmentation, or decreasing brown discoloration by blocking the pathway of pigment synthesis, according to both Herrmann and Guanche.

Side Effects of Vitamin C

Generally, vitamin C is safe for daily use. However, in high concentrations, it can be irritating, especially if mixed with other acids. Herrmann says those with extremely sensitive skin may not be able to tolerate it, and in which case, should avoid it. Many vitamin C products are also oily, which can be problematic for those with oily skin, so Herrmann recommends consulting your board-certified dermatologist to find a brand or product that is best suited for your skin type. 

How to Use It

One highly debated topic when it comes to vitamin C is what time of the day is best for application. While some argue that morning is best for protecting the skin, others are in favor of nighttime when the skin's vitamin C is most depleted. According to Herrmann, consistency is most important, whether you decide to apply it in the morning or before bed, but avoid using it at the same time as benzoyl peroxide. She also suggests using it daily or every other day, and if you're using a serum (the most common vehicle for vitamin C), apply it after cleansing.

Formulation Considerations

As great as it is, vitamin C isn't without obstacles. First of all, it's inherently unstable and reactive and easily loses its antioxidant properties when exposed to heat, light, and air. As a fix, cosmetic companies have been jumping on the powder form of vitamin C to help improve stability, which would, in theory, make it last longer and increase the shelf life.

Unfortunately, though, Herrmann says it’s not as simple as just mixing one part C-powder to one part of your favorite moisturizer; Vitamin C also does not easily penetrate the skin's barrier. "Depending on the skincare formulation, applying vitamin C can do absolutely nothing or can work as a powerful antioxidant," adds Guanche.

To be effective, Herrmann says vitamin C must be in a concentration of at least 10 percent, and the pH of whatever you’re adding it to must be acidic to allow for its absorption. "It’s hard to know the pH of products, and even if you get it right, the powder can crystallize on the skin before it has a chance to absorb, which is a must-do for efficacy." For this reason, Herrmann advises against the DIY trend. "I think it’s wiser to stick with high-quality products that have resulted from extensive research and development to make sure their vitamin C is made available in an optimal formulation for enhanced stability and skin penetration," Herrmann says.

Herrmann also recommends seeking well-researched forms of vitamin C—like L-ascorbic acid—and opting for formulas that also contain vitamin E, which helps to stabilize vitamin C.