Vitamin C is the most important antioxidant found in skin. Unfortunately, human beings do not possess the enzyme L-glucono gamma lactone oxidase to make vitamin C. Therefore, it must be obtained externally.
Vitamin C’s active form, L ascorbic acid, is responsible for its biologic effects. Vitamin C is the second most researched ingredient in skincare, after retinoids. There are many benefits to ascorbic acid. Numerous studies have proven that it can prevent UVA and UVB photodamage. It stimulates collagen production and acts as a cofactor for enzymes involved in collagen production. Vitamin C is also a powerful lightning agent. It blocks the enzyme tyrosinase which is a key component in melanin production.
Vitamin C is however highly unstable. Vitamin C is easily affected by heat, light, pH changes, and other ions. These factors have led to the development of vitamin C derivatives which are stable and retain their efficacy. But formulation remains a challenge. It is important to demonstrate ingredient effectiveness not only in the laboratory or on animals but also on humans. There is a lack of data on skincare ingredients, and many publications have conflicting information. While one study might show the benefits of a derivative, another may not. This demonstrates the difficulties of manufacturing L. ascorbic acid.
Vitamin C derivatives
L -ascorbic acid
Active form of vitamin C (AA). This is the most well-studied form of vitamin C.
Concentration: 15%. The ideal range is between 10-20%. Higher than 20% does not cause skin to become more dry.
15% applied to the skin will saturate it in three days and then decrease by 50% in four days. It is impossible to wash off once it has penetrated the skin.
Combining 1% vitamin E with 0.5% ferulic Acid will increase the stability and antioxidant benefits 8 times more.
The most widely published studies on vitamin C serums have been done by Skinceuticals CE Ferulic. Skinceuticals holds a patent (U.S. Pat. No. 7,179,841 patent on this formulation. Since then, many dupes have been developed for Skinceuticals, but they do not contain the exact formula and lack clinical trials.
Magnesium and sodium ascorbyl phosphate
Salt is required to make L-ascorbic acids. Effectiveness is dependent on the skin’s conversion of SAP/MAP into AA.
There have been mixed results in studies on efficacy. While there are few studies that show problems with percutaneous absorption in some studies, others in vivo or in vitro studies have shown benefits.
These molecules are charged and should be prepared at a neutral pH to aid skin penetration.
Ascorbyl glucoside (AA-2G)
For photodegradation protection, glucose (sugar), group modified to AA. AA-2G can be converted to AA using the skin enzyme a-glucosidase. This allows for a more sustained release of vitamin C. However it is also less irritative than AA.
3-O ethyl ascorbic Acid (3OAA)
Ethylated vitamin derivative. It is stable at different temperatures and is most often used in Asian skincare to brighten skin.
It is similar to AA-2G but less effective than AA. Although it is promising as an antioxidant or tyrosinase inhibitor, studies on its effects on neocollagenesis are very limited.
Lipophilic ester of AA is one of the most unstable vitamin C derivatives due to its chemical structure. Since it’s lipophilic, it can penetrate the skin better.
It has been shown to have anti-aging and antioxidant properties. It is not as effective at converting skin to AA, like MAP/SAP. One study found that UVB exposure to ascorbyl palmitate can actually increase lipid oxidation and cause more skin oxidative damage.
Pro vitamin C is a stable, lipid-soluble form that can be converted to AA by the skin. It penetrates skin 4x better than MAP. It is lipophilic, meaning it can penetrate the dermis where AA cannot. It may be less irritating than AA, but smaller studies have suggested it to be potentially more potent.
Ascorbyl Tetraisopalmitate (ATIP)
ATIP, a lipid-soluble form of vitamin A with a slightly different chemical structure, is similar to tetrahexyldecyl ascorbate. Studies in vitro have demonstrated a conversion rate of 84% to AA. It is stable and has a shelf life of 6-12 months.
Finally, personal use is limited to products proven to be safe in clinics. SkinceuticalsCE Ferulic has had the greatest number of studies to date. Other products, such as Vichy Peptide C and Skinbetter Alo Defense and C+ Correcting Complex, are promising and supported by studies.