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Chiral Skin Care
By: Shyam Gupta, PhD, and Linda Walker
Posted: November 5, 2010, from the November 2010 issue of GCI Magazine.
The left-handed and right-handed molecules usually have different physical, chemical and biological properties.
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The applications of chiral ingredients in skin care and other topical products are also abundant.
Before discussing how these ingredients work, a quick analogy: People are either right-handed or left-handed. Right-handed people work better with their right hand; left-handed people work better with their left hand. Very few people are ambidextrous, working equally well with their right or left hand.
Just like people, these right-sided or left-sided natural ingredients perform uniquely in many cases—as previously touched upon in the amoxicillin example. A left-handed ingredient can have a greater skin wrinkle reduction benefit than a right-handed ingredient—ascorbic acid being a prime example. An L ingredient can be skin soothing, while the same ingredient in its D-form may cause skin irritation. If skin irritation property of a D-form is greater than skin soothing property of an L-form, then the DL-form may cause skin irritation overall. The use of pure 100% L form in such cases, for example, is essential.
Natural ingredients included in a cosmetic product that are either L or D, too, may not absorb into skin at the same rate. If an L ingredient is absorbed more rapidly, then a 50:50 mixture of both L and D ingredients may have less beneficial effects compared to the use of a 100% pure L ingredient. If the ingredient has been made via synthesis in a pure L- or D-form, then both the natural and the synthetic would provide the same and equal biological properties. Synthetic ingredients are not bad, as long as they are nature-equivalent and have no undesirable chemical impurities. Examples follow.
Chirality in ascorbic acid: Ascorbic acid is a sugar acid possessing two chiral carbon atoms. The L-form of ascorbic acid is commonly known as vitamin C. A recent study has shown that D- and L-forms of ascorbic acid have different affinity for the enzyme tyrosinase, which catalyzes the production of melanin and other pigments. This would indicate that the skin-whitening efficacy of L-ascorbic acid and D-ascorbic acid are vastly different. The efficacy of protective effects of D- and L- ascorbic acid on light-induced retinal damage in rats in one study showed vastly different biological efficacy of these isomers. In addition, 5-lipoxigenase, an enzyme causing cellular oxidative damage, is selectively inhibited by L-ascorbic acid; D-ascorbic acid reverses this beneficial effect.