| DERMATOLOGY | PEER-REVIEW
ABSTRACT Antioxidants have become increasingly popular as cosmeceuticals due to the beneficial effects they exert on oxidative
deficiency as the main cause of scurvy2
and some animals, humans are unable to synthesize vitamin C due to the absence of an enzyme called L-glucono-gamma lactone oxidase. Therefore, we rely entirely on oral supplementation either in the form of tablets or diet (citrus fruit and green leafy vegetables), and topical application in the case of cosmeceuticals for the skin3
V . With increasing evidence of the protective
effects of vitamin C and its derivatives on the skin, vitamin C has become a popular cosmeceutical agent. Biochemically, vitamin C has a 5-hydrocarbon ring similar to that of fructose4
. When ingested in usual doses
of up to 100 mg per day, complete absorption of vitamin C occurs in the distal small intestine. The plasma half-life is reported to be between 8–40 days. With higher levels of intake, more rapid renal excretion occurs and the half-life
stress and free radicals generated by exogenous factors such as pollution and solar radiation. Vitamin C is the main antioxidant in the skin and has been used
ITAMIN C IS THE MOST ABUNDANT antioxidant in human skin1
extensively for this purpose. This article details some of the physiologic properties of vitamin C as well as its main mode of action.
is thought to decrease markedly to about 30 minutes5 . The
importance of vitamin C for our health was signified in 1937 by Dr Albert von Szent-Györgyi who won the Nobel prize for discovering vitamin C . Unlike plants
.
Absorption of oral vitamin C is limited by active transport mechanism and despite high doses of oral supplementation, only a small fraction of it will eventually be biologically available and active in the skin. Hence, for any discernible role of its actions in the skin, vitamin C needs to be supplied topically2
.
Topical formulations of vitamin C Vitamin C is available in a number of active forms. Among all the available options, L-ascorbic acid is the most biologically active and well-studied3
. L-ascorbic acid is a
hydrophilic and unstable molecule, hence the poor penetration into the skin due to the hydrophobic character of the stratum corneum. L-ascorbic acid is also a charged molecule, which further limits its penetration6
.
The instability of the molecule (it degrades upon exposure to air and light) means that for L-ascorbic acid to be able to remain stable and penetrate through the stratum corneum, it needs to be formulated in a way that provides both stability and permeability. An effective method of achieving this is by reducing the acidity of
FIRAS AL-NIAIMI, MD, Consultant Dermatologist, Sk:n Clinics, London, UK,
email:
firas55@hotmail.com
KEYWORDS Antioxidant, ascorbic acid, photoaging, photoprotection, vitamin C
prime-journal.com | January/February 2016 25
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