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Learn the truth about vitamin C serums as the experts at Kiehl’s expose common myths about vitamin C in skincare. Discover how vitamin C benefits your skin and how to use it in your skincare routine.

the truth about vitamin c for skin

Kiehl’s became pioneers in vitamin C skincare when our chemists stabilised 10.5% vitamin C in our potent vitamin C serum formula. This customer favourite is formulated with 12.5% vitamin C* and hyaluronic acid and penetrates skin's deeper surface layers to help visibly reduce lines and wrinkles, minimise the appearance of pores, help firm skin and boost radiance. With 10.5% L-Ascorbic Acid and 2% vitamin Cg, the antioxidant vitamin C in our patented formula remains in the skin for up to 6 days.

From boosting radiance, to helping diminish signs of aging, to antioxidant protection, vitamin C is a highly efficacious skincare ingredient with a wide range of benefits.I With all of the myths and misinformation circulating about vitamin C, let's unravel the truth about the benefits of using a vitamin C face serum. Discover more about this trusted ingredient and how to choose the best vitamin C skincare to use in your daily skincare routine.

Fact: Not All Vitamin C Serums are Created Equal

There are actually several different forms of Vitamin C that are used in skincare formulas. While they have overlapping benefits, Pure Vitamin C (L-Ascorbic Acid) is absorbed into skin and starts working immediately upon contact while Vitamin Cg (Ascorbyl Glucoside) activates once absorbed into the upper layers of skin to boost Vitamin C activity over time. Kiehl’s Vitamin C serums and formulas effectively incorporate a form of topical Vitamin C that is carefully selected to maximize its targeted efficacy.

Fiction: The More Vitamin C, the Better

While it may seem like a higher level of Vitamin C would be better, these formulas can actually cause sensitivity or be less effective if they are not stabilized properly. When products have concentrations of L-Ascorbic Acid that are too high, skin can even experience irritation. Kiehl’s selects the best forms of stabilized Vitamin C at concentrations that are both efficacious and gentle. Our vitamin C skin serums are then dermatologist-tested for safety, demonstrating the suitability of our formulas for all skin types, including sensitive skin.


From dark circles, to crow’s feet, Vitamin C eye serums can also help brighten and smooth the eye area. When selecting an eye serum, look for a formula carefully designed for the delicate eye area. Kiehl’s Powerful-Strength Line-Reducing & Dark Circle-Diminishing Vitamin C Eye Serum with Pure Vitamin C, Tri-Peptide and Hyaluronic Acid is dermatologist- and ophthalmologist-tested for safety. This efficacious formula delivers the benefits of Vitamin C to your eye area for a fresher, brighter appearance.

Fiction: DIY Vitamin C Serums are as Effective as Other Formulas

L-Ascorbic Acid is an unstable ingredient, meaning it can be oxidized when it is exposed to light, air or heat and become less effective. This powerful form of Vitamin C can be very hard to stabilize within serums and needs to be formulated at a specific pH level to ensure that it effectively delivers benefits to skin. Kiehl’s became pioneers in Vitamin C skincare when we first stabilized L-Ascorbic Acid in our water-free formula more than 15 years ago.

“When exposed to water, Pure Vitamin C can degrade causing it to lose its effectiveness. A water-free formula (like Powerful-Strength Line-Reducing Concentrate) helps keep high concentrations of Pure Vitamin C stable and effective.” – Dr. Megan O’Brien, Kiehl’s Consulting Dermatologist

Fact: Your Skin Needs Topical Vitamin C

Just as Vitamin C is an essential part of your diet, it is also an important step in your skincare routine. The human body does not produce its own Vitamin C but relies on obtaining it through nutritional and topical applications.II Daily use of a balanced and stabilized Vitamin C facial serum will ensure that your skin soaks up all of the perks of this powerful ingredient.

Fiction: Vitamin C Serums Cause Skin Sensitivity to the Sun

In actuality, topical Vitamin C has been demonstrated to be a second line of defense against harmful UVA rays while also helping to bolster skin’s antioxidant defenses. We recommend applying a Vitamin C serum in the morning before adding a daily sunscreen.III

Fact: Vitamin C Products Benefit All Skin Types

The Vitamin C serum benefits extend to all skin types, including sensitive and dry skin. In addition to helping visibly fade discolorations or diminish fine lines and wrinkles, using a Vitamin C serum can also provide antioxidant protection to help defend from skin-damaging free radicals.

Fiction: Vitamin C Serums are Not Suitable for Sensitive Skin

At Kiehl’s our Vitamin C serums are carefully formulated to provide gentle skincare for sensitive skin and are tested on panels of 50% sensitive skin individuals. When first beginning to use a Vitamin C serum, start with a once-daily application and gradually build to twice a day. Always consult with your dermatologist when incorporating new skincare products into your routine.

Fact: Store Your Vitamin C Serum in a Cool, Dry Place

Store L-Ascorbic Acid serums in a place other than your bathroom cabinet as they are best kept in an area without humidity. Additionally, L-Ascorbic Acid serums in dark-colored or amber bottles can help protect the formula from light.


While retinol and vitamin C cannot be directly layered, we highly recommend incorporating these ingredients in separate morning and night routines for powerful anti-ageing benefits. Retinol (or vitamin A) works by accelerating the skin cell cycle bringing newer, fresher skin to the surface. This anti-aging ingredient improves signs of ageing, reduces breakouts and excess oil flow, and brightens dulled skin. When used alongside vitamin C, expect to see a visible improvement in dark spots and signs of ageing for youthful-looking skin. We recommend using your vitamin C face serum like the Clearly Dark Spot Serum in the AM and the Retinol Micro-Dose Serum in the PM.

Fact: Apply Vitamin C Serums Before Your Moisturizer

After you cleanse and tone your skin, apply a thin layer of your vitamin c skin serum. Smooth it on morning and night before your moisturiser to help lock in the skin benefits of your vitamin C serum. We recommend following with a nourishing moisturiser like the Ultra Facial Cream with Squalane to hydrate and protect skin.

Fiction: Vitamin C Serums are Only for the Daytime

While Vitamin C help defends skin during the day, it is also an efficacious ingredient to use in your nighttime skincare routine. In our formula, the antioxidant Vitamin C remains in skin for up to 6 days! For best results, use your Vitamin C serum twice a day, morning and night. Be sure to always use SPF in your morning routine to protect skin from UV rays.

Fact: Vitamin C Serums are Not Just for Anti-Aging

Vitamin C levels deplete in skin over time so using vitamin C skin care to help target the signs of ageing like fine lines and wrinkles is important as you grow older. However, vitamin C skincare also has other benefits besides anti-ageing, including reducing the appearance of dark spots and helping you achieve crystal-clear glass skin.

Types of Vitamin C in Skincare

As discussed, there are several forms of vitamin C all with unique benefits depending on your skincare goals. Let's deep dive into the different forms of vitamin C and how they differ from each other:

Pure Vitamin C

L-Ascorbic Acid, or Pure Vitamin C, is a powerful skincare ingredient that easily absorbs into skin and begins working immediately. A dermatologist-recommended ingredient, L-Ascorbic Acid is frequently used in anti-aging skincare products to improve radiance and skin texture while helping to diminish the appearance of fine lines, wrinkles and crow’s feet.


Vitamin Cg

Vitamin Cg, or Ascorbyl Glucoside, is a potent derivative of Vitamin C that provides antioxidant protection and helps to minimize the visible signs of aging. Kiehl’s Powerful-Strength Line-Reducing Concentrate is formulated with 2% Vitamin Cg to help enhance the efficacy of Vitamin C benefits over time.IV


Activated C

Activated C is a next-generation Vitamin C derivative that is highly efficacious. Within our formulas, this powerful form of Vitamin C penetrates skin’s surface and is known to help fade dark spots and skin discolorations. Activated C is a key ingredient in Kiehl’s dark spot corrector and brightening face mask.


*With 10.5% Pure Vitamin C and 2% Vitamin Cg
I Collagen Metabolism. Diegelmann, RF. 5, 2001. Wounds, Vol. 13.
II Topical vitamin C in aging. Colvin, RM and Pinnell, SR. 1996, Clin Dermatol, Vol. 14, pp. 227-234.
III Enzymatic and non-enzymatic antioxidants in epidermis and dermis of human skin. Shindo, Y, et al. 1994. J Invest Dermatol, Vol. 102, pp. 122-124.
IV Double-blind, half-face study comparing topical vitamin C and vehicle for rejuvenation of photodamage. Fitzpatrick, RE. and Rostan, EF. 3, 2002. Dermatol Surg. Vol. 28, pp. 231-236.

How to Use Vitamin C Skincare

Now that you know the benefits of vitamin C serums for the skin, let's unpack how to add this ingredient to your routine. We recommend following these steps:


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