**9. Formulating vitamin C for topical/cosmetic use**

There are numerous studies that support and justify the topical/cosmetic use of vitamin C. Among its actions, we can highlight its ability to eliminate ROS, its action as a cofactor for the enzymes prolyl and lysyl hydroxylase, responsible for the stabilization and cross-linking of synthesized collagen by fibroblasts, the stimulation of collagen synthesis directly by activation of messenger ribonucleic acid (mRNA) and

the preservation of collagen in the skin by regulating the enzymes responsible for its degradation [19].

Oral vitamin C supplementation is less effective than topical, as its absorption is limited by intestinal transport mechanisms, so the topical route is the one of choice when we want to increase the concentration of vitamin C in the skin [24].

Vitamin C in its active form L-ascorbic acid is hydrophilic (water-soluble) and very unstable, and this characteristic conditions its skin absorption due to the hydrophobic nature of the stratum corneum. The first preparations of vitamin C for topical use presented the problem of its rapid oxidation of ascorbic acid in dehydroascorbic acid on contact with air and metals or if they were preserved at high temperatures.

For a good penetration through the epidermis, several studies report that the optimal pH of the preparation has to be less than 3.5, and this pH is achieved with the addition of ferulic acid that acts as a stabilizer of the L-ascorbic acid molecule.

Different strategies have been tested to solve the problem of the stability of vitamin C, such as encapsulation, formulation at low pH, oxygen-tight packaging, and the addition of electrolytes and other antioxidants [25].

The optimal concentration will depend on the type of formulation and presentation but should always be greater than 8% and less than 20%, higher concentrations have been irritating and have not offered an increase in their activity, and may be formulated alone or associated with other active ingredients [26].

The cosmetic industry has sought greater stability and easier formulation with derivatives such as ascorbyl 6 palmitate, magnesium ascorbyl phosphate, sodium ascorbyl phosphate, ascorbyl 2-glucoside, ascorbyl 2-phosphate6-palmitate, and 3-O-ethyl ascorbate [26].

Among the nonsaline derivatives of ascorbic acid used in formulations intended for topical use, we highlight:


The search for improvement in activity and skin penetration of vitamin C on the skin has led to clinical studies using the DNA aptamer: "Aptamin C". Studies such as

*Cosmetic Topical Use of Vitamin C DOI: http://dx.doi.org/10.5772/intechopen.109644*

that of Choi, S. et al. demonstrate the effectiveness *in vivo* and *in vitro* of this aptamer that binds specifically to vitamin C and inhibits its oxidation [27]. Aptamers are single-stranded DNA or RNA sequences that adopt unique three-dimensional structuresthat allow them to recognize a specific target with high affinity [28].
