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Vitamin C is one of the most common antioxidants found in skin care products. According to Dr. Leslie Baumann‘s textbook Cosmetic Dermatology, topical application of vitamin C has been found to protect against UV-induced erythema and sunburn, to increase fibroblast production of collagen, and to possibly reduce wrinkle formation. For more on vitamin C and its derivatives in skin care products, read on!

Why use vitamin C in topical skin care?

According to the International Journal of Pharmaceutics, vitamin C has many favorable aspects for the skin, including:

• scavenging of free radicals (reacts with the superoxide anion or the hydroxyl radical);
• suppressing pigmentation of the skin (by inhibiting the enzyme tyrosinase);
• decomposing melanin;
• triggering collagen production and thereby increasing skin firmness;
• enhancing sunscreen protection (see below).

Dr. Jeannette Graf also adds in Dr. Burgess’s Cosmetic Dermatology text:

• “Topical vitamin C increases levels of tissue inhibitors of collagen-degrading matrix metalloproteinases (MMP-1). “

According to a study in the British Journal of Dermatology, topical application of vitamin C has been shown to prevent UVA-mediated phototoxic reactions in porcine [pig] skin, as well as to supplement depleted vitamin C levels after UVA exposure. According to the Journal of Photochemistry and Photobiology, UVA-induced damage includes the release of oxidative species, resulting in immunosuppression, photodermatoses, photoaging and photocarcinogenesis.

In addition, according to the study in the British Journal of Dermatology, topical application of vitamin C also protected skin from UVB-induced damage, as measured by erythema and sunburn. According to the Journal of Photochemistry and Photobiology, UVB-mediated damage includes activation of MAPK and NF-κB pathways that can result in erythema, hyperplasia, hyperpigmentation, immunosuppression, photoaging and skin cancer.

How does the efficacy of vitamin C compare to that of other antioxidants?

Based on a 2006 study by McDaniel et. al, vitamin C is less effective at reducing oxidative stress than similar concentrations of idebenone or vitamin E, kinetin, or ubiquinone. Other potent antioxidants anticipated to be more effective than vitamin C, such as CoffeeBerry and green tea, were not included in the study. However, in the study, vitamin C was found to be more effective at reducing oxidative stress than lipoic acid.

According to The Journal of Cosmetic Dermatology, the above ranking of antioxidants was found via a multistep sequence of in vitro and in vivo methods. In vitro methods included using UV-induced radical trapping/scavenging capacity measured by photochemiluminescence, pro-oxidative systems (LDL-CuSO4, microsome-NADPH/ADP/Fe3+) with measurement of primary and secondary oxidation products, UVB irradiation of human keratinocytes, and in vivo evaluation, using the human sunburn cell (SBC) assay. Correlation and trends between in vitro and in vivo results were established, and the standardized test protocol was used to quantify oxidative stress protection capacity of antioxidants.

What are all of the different forms of vitamin C available in skin care products?

L-ascorbic acid is the most common form of vitamin C used in skin care. It is water-soluble. The advantage to L-ascorbic acid is that its concentrations are well-established in skin care products; for instance, CellexC contains 10% L-ascorbic acid and Skinceuticals CE Ferulic ($103.70, Amazon.com) contains 15% L-ascorbic acid. It has been shown that topical application of CellexC, with 10% L-ascorbic acid, results in the presence of L-ascorbic acid in the skin days after application, with an increase in the level of collagen as well. Unfortunately, it is well known (and reported here in the journal Die Pharmazie) that L-ascorbic acid changes upon exposure to light, heat, or air. In particular, L-ascorbic acid is reversibly oxidized to L-dehydroascorbic acid, at which point it may then be irreversibly oxidized to diketogulonic acid, which is inactive. For this reason, numerous substitutes to L-ascorbic acid are used in skin care.

Ascorbyl palmitate is a fat-soluble ester of L-ascorbic acid; it is L-ascorbic acid combined with palmitic acid, a fatty acid. According to a 1997 study, the ascorbyl palmitate is more stable than L-ascorbic acid. A 2001 study in the International Journal of Pharmaceutics found that the stability of ascorbyl palmitate was increased further when ascorbyl palmitate was used in high concentrations (1-2%), or placed in water-in-oil emulsions rather than oil-in-water emulsions, due to the relocation of the unstable cyclic ring to the internal aqueous phase in the water-in-oil emulsions. Given that ascorbyl palmitate concentrations are generally 0.05-1%, unless a higher concentration of ascorbyl palmitate is established for a product, sodium ascorbyl palmitate or magnesium ascorbyl palmitate have been found to be more stable in solutions (see below).

Sodium ascorbyl palmitate is a water-soluble form of L-ascorbic acid; it is L-ascorbic acid combined with palmitic acid, a fatty acid, and – you’ll never guess – sodium. According to a 2001 study in the International Journal of Pharmaceutics, sodium ascorbyl palmitate has greater long-term stability than ascorbyl palmitate when each is used in similar concentrations. Unlike ascorbyl palmitate, sodium ascorbyl palmitate is stable in water-in-oil emulsions and oil-in-water emulsions.

Magnesium ascorbyl palmitate is a water-soluble form of L-ascorbic acid. According to a 1997 study in the Journal of Pharmaceutical and Biomedical Analysis, magnesium ascorbyl palmitate has greater stability than both L-ascorbic acid and ascorbyl palmitate, like sodium ascorbyl palmitate. (As far as I know, no peer-reviewed published studies have compared the efficacy and stability of magnesium ascorbyl palmitate and sodium ascorbyl palmitate.)

Ascorbyl glucoside. Ascorbyl glucoside has a structure in which the C2-hydroxyl group of L-ascorbic acid is masked with glucose. According to the manufacturer, Hayashibara International, once ascorbyl glucoside is selectively permeated through the skin, it is broken down into L-ascorbic acid and glucose by the enzyme alpha-glucosidase. Essentially, because ascorbyl glucoside is broken down into L-ascorbic acid, it has the same functions as L-ascorbic acid! In addition, ascorbyl glucoside has been found to have greater stability in the presence of air, heat, light, and pH changes than L-ascorbic acid.

Ascorbyl glucosamine is L-ascorbic acid combined with (yes, this is obvious) glucosamine. Although the combination of N-acetyl glucosamine (NAG) and niacinamide was shown to reduce facial hyperpigmentation in Japanese and Caucasian subjects with facial hyperpigmentation in two double-blind, vehicle-controlled, split-face, left-right randomized clinical studies, use of a formulation with 5% ascorbyl glucosamine was shown to be less effective in reducing hyperpigmentation than 20% azelaic acid (source: Dermatology).

According to Dr. Burgess’s Cosmetic Dermatology textbook, “the most stable vitamin C preparations remain anhydrous or completely water-free.”

Can vitamin C really reduce wrinkles?

According to Dr. Leslie Baumann‘s textbook Cosmetic Dermatology, there is only one study in the literature that studies the effects of vitamin C on wrinkles. In the study, CellexC with 10% L-ascorbic acid ($90.00, AstonishingSkinCare.com) was used in a split-face study for three months, and was found to decrease wrinkles (as measured by photography assessments and optical profilometry). However, as Dr. Baumann states, “the study cannot be considered as a blinded study because a large population of the patients experienced stinging on the side treated with vitamin C. However, there was a significant difference in the wrinkles on the treated side versus the untreated side.” Baumann speculates reasons for this may be increased collagen synthesis or inflammation from the product.

What’s the advantage to using vitamin C and vitamin E together?

According to Dr. Leslie Baumann’s Cosmetic Dermatology textbook, vitamin C and vitamin E are network antioxidants that have been found to synergistically enhance the power of one another. (When one antioxidant is depleted, it can essentially “borrow” an electron from the other antioxidant to renew itself, and vice versa). Vitamins C and E as L-ascorbic acid and tocopheryl acetate have also been reported by Djerassi et. al. to prevent the formation of carcinogenic nitrosamines. Vitamin C and vitamin E have also been shown to enhance the photoprotective effects of sunscreen, as vitamin C has been reported to enhance UVA protection, whereas vitamin E is more effective against UVB radiation.

Lastly, vitamin C has also been found to decrease hyperpigmentation, although a study in the International Journal of Dermatology found that 4% hydroquinone was more effective in treating melasma than vitamin C as L-ascorbic acid. However, a separate study, also in the International Journal of Dermatology, found that combination therapy of 4% hydroquinone, vitamin C, vitamin E, and 10% glycolic acid was effective in treating signs of hyperpigmentation.

Vitamin E is naturally produced in sites rich in sebaceous glands, as it is physiologically delivered to the surface via secretion of sebum, according to this article in the journal Skin Pharmacology and Physiology. According to a second research study, this study by Packer and Valacchi, vitamin E may be the predominant natural antioxidant both in murine and human skin, and it shows a characteristic gradient with lower levels towards the outer stratum corneum layers.

I know I’m just learning, but in my opinion…

Vitamin C has been proven to increase protection against free-radical damage, to increase collagen production, and to decrease tyrosinase activity. Unfortunately, L-ascorbic acid is not very stable upon exposure to heat, light, and air. This is unfortunate, because concentrations of L-ascorbic acid in skin care products and their effects have been widely studied, while the concentrations of other forms of vitamin C and their effects are not as established yet. I would love to see studies on how, say, 15% L-ascorbic acid compares to 2% ascorbyl palmitate and 2% ascorbyl glucoside upon first opening the package and after several uses of each product. At any rate, I hope you found this helpful, and I would love to learn (and publish) more from anyone with information!