Vitamin C is an essential vitamin for maintaining a healthy body and healthy skin. Yet, the body cannot synthesize vitamin C from glucose, because it lacks the enzyme required for this reaction. As a result, humans rely on dietary intake for their supply of vitamin C in the body, which can be ingested from food sources, such as citrus fruits and dark-green leafy vegetables. Unfortunately, ingested vitamin C cannot deliver an adequate amount of L-ascorbic acid to the skin. If antioxidants could be delivered in high concentration through the stratum corneum into the skin, then the antioxidant protective reservoir could be increased, and photoprotection and skin cell repair could be enhanced. More importantly, skin cell rejuvenation and collagen synthesis could be increased.1
The skin relies on antioxidants for protection against such environmental insults as ultraviolet (UV) rays, cigarette smoke and pollutants that can cause free radicals and photoaging of the skin. Free radicals damage DNA, proteins and lipids, which cause skin cells to die. Since the skin receives the most intense free-radical assault from UV light exposure, replenishing and increasing the antioxidant defense of the skin becomes an attractive strategy for photo protection and photo repair. Studies show that, when applied to the skin, L-ascorbic acid stimulates collagen synthesis, provides sun protection and protects the skin by reducing free radicals that would otherwise destroy skin cells and their components. Topical vitamin C has also been shown to improve skin texture and tone, reduce brown spots, decrease the appearance of fine lines and wrinkles, and help prevent their formation.2
L-ascorbic acid is one of the most abundant and most powerful antioxidants in the skin and body. It is the primary water-soluble, nonenzymatic biologic antioxidant in human tissue that protects the body from oxidative stress. It is important to note that water-soluble antioxidants act as a first defense against free radicals generated in plasma, but they cannot scavenge lipophilic (fat-soluble) free radicals within the membranes. Lipophilic antioxidants—particularly vitamin E—suppress oxidative damage efficiently in membranes. In addition to its direct antioxidant effects, L-ascorbic acid is known to be the primary replenisher of vitamin E, the most efficient inhibitor of lipid peroxidation in cell membranes.3
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Formulation characteristics are critical for the delivery and penetration of L-ascorbic acid into the skin to restore and enhance its natural antioxidant activity. The major formulation characteristics are related to the following:
- Molecular structure of the vitamin C;
- Concentration of the L-ascorbic acid;
- The pH of the L-ascorbic acid serum; and
- The proper packaging of the L-ascorbic acid.
Molecular structure and concentration
Available scientific data has allowed the production of oral vitamin C in appropriate amounts to supplement the diet to maintain serum L-ascorbic acid levels for normal systemic metabolic function.4 However, the challenge to determine the appropriate chemical form of vitamin C, the appropriate pH and concentration of vitamin C, and the appropriate preparation has been elusive until the past few years. A study published by the American Society for Dermatologic Surgery demonstrated that L-ascorbic acid, which is true vitamin C, is the chemical derivative of vitamin C that is chemically reactive and bioavailable. Other derivatives of vitamin C, including magnesium ascorbyl phosphate, ascorbyl-6-palmitate and dehydroascorbic acid, did not increase skin levels of L-ascorbic acid. These are vitamin C-related molecules that moisturize the skin, but have not been shown to penetrate the skin and do not increase L-ascorbic levels in the skin. In this study, Sheldon Pinnell, MD, demonstrated that free L-ascorbic acid is the only molecular structure proven to penetrate into the skin and neutralize those damaging free radicals. Therefore, simply because a vitamin C derivative is in a product does not mean it is effective—unless it is L-ascorbic acid. This highlights and magnifies just one of the problems of vitamin C products on the market today.5, 6
In addition, many preparations lack a sufficient concentration of free L-ascorbic acid for biologic activity and penetration. L-ascorbic acid concentrations were tested from 5–30%.6 Maximal tissue levels were obtained at L-ascorbic acid concentrations of 20% and maximal concentration for optimal percutaneous absorption was 20%. Tissue levels were saturated after three daily applications, and the half-life of tissue disappearance was about three days.6
pH and stability
Many vitamin C preparations also are not pH-adjusted for optimal biologic activity and penetration. The pKa, or acid dissociation, for L-ascorbic acid is 4.2. The pKa of an ingredient is the pH level where half of the molecule is free acid and biologically active, and the other half is bound and not biologically active. When pKa = pH, there is equal concentration of the acid to its conjugate base. Tissue levels of L-ascorbic acid were enhanced only for formulations with a pH less than 3.5.6 Preparations with a pH higher than 4.0 will oxidize the L-ascorbic acid in the product. Therefore, the molecule must be un-ionized and formulated at pH levels less than 3.5 to penetrate the skin. An appropriate pH of 3.0 will maximize biologic activity, penetration and effectiveness while avoiding skin irritation with a product where the pH is too low (particularly less than 2.5). An ideal pH is between 2.6–2.8.
To evaluate your products for effectiveness, check the ingredient list. Look for products containing L-ascorbic acid and not ascorbyl palmitate, at a concentration of 20%. Many times the concentration will be listed in product materials. If not, an ingredient’s concentration can be obtained by contacting the manufacturer. The company should also be able to tell you the pH of the product to verify it’s within the ideal range.
Equally important for the penetration and benefits of a vitamin C product is proper packaging. Vitamin C oxidation is due to the reaction between oxygen and light—especially UV rays. UV rays are the portion of light absorbed by vitamin C, which causes the oxidation of L-ascorbic acid. Some topical vitamin C preparations often lack stability when exposed to air and light, which causes oxidation of the L-ascorbic acid, not only making it ineffective, but also causing it to potentially increase the formation of free radicals. The bottom line: The presence of vitamin C in a product does not guarantee its effectiveness.
To produce an effective vitamin C preparation, a temperature- and light-controlled room should be used and as much air as possible should be expelled from the container prior to packaging. This produces a stable aqueous formulation of L-ascorbic acid in an appropriate 20% free acid concentration with a pH of 3.0 +/- 0.4 to maximize biologic activity and penetration contained in an appropriate package. This allows L-ascorbic acid delivery into the skin and provides photo-protection against both UVB and UVA phototoxicity by a mechanism that is clearly not a sunscreen effect, but accomplished by neutralizing free radicals created by UV damage, as well as cigarette smoking and environmental pollutants.
This concept also applies to foods containing vitamin C and their retention of vitamin C activity. Fruit that is cut prematurely will often turn brown and wilt if left out in the air. When placed in air-tight containers and refrigerated, fruit appears fresher, longer. This temperature effect is important with most ingredients and has some relevance to all vitamin C products. That is, high temperatures increase oxidation of L-ascorbic acid and other ingredients.
Studies show that an L-ascorbic serum at a pH of 3.0 with a free acid concentration of 20% in a light-protected package maximizes biologic activity and penetration into the epidermis.6 Research also demonstrates that daily application produces an L-ascorbic acid concentration more than 20 times the normal levels after three consecutive days of application and maintains these levels with daily use.6 From a scientific standpoint, these levels are maintained for three days in the skin after the application of an appropriate vitamin C serum product is stopped.
It is important for clients to keep the lids of vitamin Cskin care products on properly as all are subject to oxidation over time. However, antioxidants such as vitamin C can begin oxidizing within minutes, while a peptide moisturizer may take months to oxidize. Remind clients not to leave the lids off their vitamin Cproducts any longer than necessary when applying, and look for products with airless or air-tight packaging that blocks out UVA and UVB light.
The body protects itself naturally from reactive oxygen species by using antioxidants to neutralize them before they cause damage to the skin cells and their components. L-ascorbic acid is one of the most abundant antioxidants in the skin. Once in the skin, studies show L-ascorbic acid stimulates collagen synthesis, provides sun protection and protects the skin by reducing free radicals that otherwise would destroy skin cells and their components.
Researchers have concluded that oral administration of L-ascorbic acid cannot generate adequate tissue levels in the epidermis for these antioxidant effects. However, to prevent photodamage to collagen and elastin and to stimulate collagen synthesis, L-ascorbic acid must penetrate the epidermis.
With regular use of an appropriate vitamin C product, you and your clients can expect to see a decrease in skin discoloration, an improved skin tone, and a decrease in the appearance of fine lines and wrinkles, along with help in preventing their formation.
- RE Fitzpatrick, Double-Blind, Half-Face Study Comparing Topical Vitamin C and Vehicle for Rejuvenation of Photodamage,American Society for Dermatologic Surgery 28 231–236 (March 2002)
- DA Guzman-Sanchez, et al., Topical Uses of Vitamin C, Skin and Aging 53–58 (March 2006)
- ZD Draelos, Vitamins and Healthy Skin, Cosmetic Dermatology, 22 8 400–403 (August 2009)
- J Keri, et al, What You Should Know About the Chemistry of Vitamin C, Skin and Aging, 79–80 (May 1999)
- NV Perricone, Topical Vitamin C Ester (Ascorbyl Palmitate), J Geriatric Dermatology 5 4 162–170 (May/June 1997)
- SR Pinnell, Topical L-Ascorbic Acid: Pecutaneous Absorption Studies, American Society for Dermatologic Surgery 21 137–142 (Feb 2001)
Lawrence Samuels, MD, is a board-certified dermatologist with a practice in St. Louis. He is a fellow of the American Academy of Dermatology, chief of dermatology at St. Luke’s Hospital and founder of Rx Systems PF.