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.

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 products 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 a 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.

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

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.

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

Other than its brightening benefits, Vitamin C is a potent antioxidant that can protect against free radical damage from UV rays and pollution. Pure Vitamin C, also known as L-Ascorbic Acid, in our Powerful-Strength Line-Reducing Concentrate, can prevent up to 90% free radical damage*** by neutralizing skin-damaging free radicals which can cause oxidative stress and early skin aging.

While many traditionally use Retinol at night and Vitamin C in the morning, you can also layer these two actives together. We recommend applying our Retinol Skin-Renewing Daily Micro-Dose Serum first, then following with our Powerful-Strength Line-Reducing Concentrate to complement the retinol’s efficacy.

The Vitamin C facial 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.

At Kiehl’s our Vitamin C serums are carefully formulated to be gentle enough 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.

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.

After you cleanse and tone your skin, apply a thin layer of your serum. Smooth it on morning and night before your moisturizer to help lock in the skin benefits of your Vitamin C serum.

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.

Vitamin C levels deplete in skin over time so using skincare products with Vitamin C is important as you grow older. However, these formulas are still effective to use before you start to see fine lines and wrinkles. These formulas help boost radiance and provide antioxidant protection to help defend skin from early signs of aging.