Pure Vitamin C for Skin: The Complete Guide

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Vitamin C
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Pure Vitamin C Benefits

Vitamin C is, without a doubt, the It skincare ingredient, one of the best-known actives, hailed as the holy grail solution to most common skin concerns. Let aside it works for all skin types, but literally, Vitamin C leaves no stone unturned when it comes to taking care of skin and, most importantly, defending it against oxidative stress. 

Who doesn't want even tone, plump skin, smooth texture, and a dewy glow? We all do, and Vitamin C is the perfect ally to help us achieve just that. This post breaks down everything you need to know about what Vitamin C is, how to build it into your routine and the skin benefits of Vitamin C.

What is Vitamin C?

Vitamin C is a naturally-occurring antioxidant that most plants and animals produce from glucose. However, people cannot synthesize Vitamin C in the body, so we can only get it from foods (think citrus fruits, green leafy vegetables, papaya) and skincare.1

Actually, it has been shown that oral Vitamin C has a low bioavailability, meaning little absorbed Vitamin C is delivered effectively to the skin; thus, topical products are preferred. In skincare, you can find Vitamin C in three main forms: L-ascorbic acid, ascorbyl-6-palmitate, and magnesium ascorbyl phosphate — L-ascorbic acid being the most active form.

Now let's dig deeper into the skin benefits of Vitamin C that make it essential in your skincare regimen.

What Does Vitamin C Do for Your Skin? Benefits of Vitamin C

As one of the most potent antioxidants, Vitamin C shields the skin against free radical damage, photo-aging, and dark patches caused by the sun. On top of that, Vitamin C has anti-aging and skin smoothing benefits by supporting collagen production. That's not all. Vitamin C has been shown to reduce melanin formation, thereby brightening dark spots and evening skin tone.2, 3

Benefits of Vitamin C for skin

  • Scavenges free radicals
  • Boosts collagen
  • Offsets photodamage
  • Brightens dark patches
  • Improves skin texture

How to Use Vitamin C on Skin

Thanks to the various skin benefits of Vitamin C, it's the main selling pitch in lots of products, from toners, serums, moisturizers, and masks — with serums being the most effective since their small molecules allow actives to sink in the skin. If you don't know when to use Vitamin C serum, the how-to and when to apply Vitamin C serum, we've got you covered. 

Layer Vitamin C serum on cleansed, toned skin before moisturizer and sunscreen (at AM). Using your Vitamin C serum at AM helps prevent free radical damage, but don't forget to follow up with at least 30 SPF sunscreen since Vitamin C can make the skin photosensitive. 

Consider using Vitamin C serum at night, too. During the night, skin is in a repairing mode, and layering Vitamin C helps boost its regenerative state while building up the antioxidant defense for the next day. "Your body builds up a storage of antioxidants as you use them," says Joshua Zeichner, the cosmetic and clinical research director at Mount Sinai Hospital in New York City. "So using Vitamin C serum at night will help guarantee your body has enough ready to go in the morning when you need them most," he adds.4

Never mix Vitamin C with AHAs and BHAs. Due to their low pH, they might unstabilize each other. More than that, such a combination might be too active and cause sensitivity or irritations. Also, you shouldn't layer Vitamin C with benzoyl peroxide as it may lower the efficacy of Vitamin C.

Pro Tip: Using Vitamin C with vitamin E is one of the best things you can do for your skin. They work synergistically in the protection against oxidative damage.5

Now that you know when to apply Vitamin C serum, let's delve into how frequently you can use it in your skincare routine.

Should You Use Vitamin C Serum Every Day?

Using Vitamin C serum daily is the key to reaping all its benefits. There's no one-size-fits-all on how often to use Vitamin C serum — the concentration and skin type matter. Suppose your skin is on the sensitive side and you're using a highly concentrated product. In that case, you want to start with three-weekly applications and gradually increase up to daily use if you're not experiencing redness or irritations. 

Should You Use Vitamin C Serum Before or After Moisturizer?

You should use Vitamin C serum before moisturizer. The rule of thumb is layering skincare products from the thinnest to thickest formula. Hence, slathering Vitamin C serum before moisturizer allows the serum's actives to enter the skin, while the moisturizer forms a veil that traps in these actives for prolonged benefits.

The Shelf Life of Vitamin C

Most Vitamin C-infused skincare products have a shelf life between one to three years. Yes, a product can keep its potency up to three years, but only if it's not opened. Once opened, our skincare products start to lose the active ingredients making us often use ineffective products. 

The ideal scenario is using freshly activated ingredients, just as a cosmetician does for in-office treatments. But is that possible with our at-home skincare products? It might be.

Does Vitamin C Serum Lose Potency Over Time?

As an antioxidant, it's easy for Vitamin C serum to lose potency as Vitamin C is oxidized in the air and degraded by light and heat. Even if Vitamin C serum is packed in a dark bottle, every time you open your product, there's a chance light, heat, and air get in and deactivate the formula, making your efforts to protect the skin against free radicals in vain.

Most brands claim it's okay to use Vitamin C serum for six months to one year after opening because they're unaware of the storage conditions. What if your Vitamin C serum turned brown and oxidized? Will it still work as an antioxidant? Nope. As soon as you notice your Vitamin C serum has a brown, dark color, it's time to toss it. 

How Long Does Vitamin C Serum Last?

As stated by labels, Vitamin C serum lasts up to six months. But manufacturers are not aware of how people store their products. Keep your Vitamin C serum in light and open it a few times, so heat and air get in, and you'll have the perfect recipe for an oxidized product that's totally useless.

According to our clinical research, it turns out active ingredients degrade by 40% on average within 8 weeks, while clean formulations degrade 4.5X faster. Yep, on day 1, when the product was first opened, the concentration of active ingredients was 30% lower than the brand claimed.

Find the Best Vitamin C Serum for You

At Exponent, results come first. That's why we developed the first self-activated skincare line featuring skincare's most effective active ingredients—including Vitamin C. Our Brightening Boost Vitamin C protects highly sensitive Vitamin C, so it never degrades and delivers the optimal results in every dose. You can also check out our Product Recommendation List to find other Vitamin C products that pass The Exponent Standard.

Brightening Boost Vitamin C Serum System

Bonus: We made a Vitamin C Test kit that allows you to test how much active Vitamin C your product actually contains.

Words By: Ana Vasilescu


  • Murad Alam, Hayes B. Gladstone, Rebecca C. Tung, Cosmetic Dermatology, 2009. Source
  • Telang PS. Vitamin C in dermatology. Indian Dermatol Online J. 2013. Source
  • Al-Niaimi F, Chiang NYZ. Topical Vitamin C and the Skin: Mechanisms of Action and Clinical Applications. J Clin Aesthet Dermatol. 2017. Source
  • Chloe Metzger. Why You Should Wear This Daytime Skin Product at Night. Allure. June 2015. Source
  • Traikovich SS. Use of topical ascorbic acid and its effects on photodamaged skin topography. Arch Otolaryngol Head Neck Surg. October 1999. Source


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