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By: Noureddine Mriouah
Posted: July 30, 2012, from the August 2012 issue of Skin Inc. magazine.
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Besides irritability, retinoids bring many challenges to skin care formulations, including water insolubility and chemical instability. Retinol and its derivatives are hydrophobic compounds that are liposoluble. They come in the form of crystals or oily solutions that are insoluble in water, but soluble in organic solvents, such as alcohol. They are also highly unstable in the presence of oxygen and other oxidants, and are highly sensitive to light. Although they are stable in alkaline environments, retinoids are very sensitive to acidic conditions.
Chemists have proposed several solutions to improve the stability of retinol and its derivatives. Among them is the use of UV-protective packaging and the addition of antioxidants, such as tocopherols, ascorbic acid, butylhydroxyanisole (BHA) or butylhydroxytoluene (BHT). Regarding the problem of solubility, other solutions include the use of different vehicles, such as emulsions and microemulsions. Other solid supra-molecular structures, such as microspheres and microcapsules—which are generally made of polymers—allow the incorporation of retinoids by improving their stability, solubility and, at the same time, their delivery.
Getting the best from retinoids
When it comes to developing new retinoid formulas, some skin care manufacturers have risen to the retinoid challenge, applying bold new techniques to temper the negative aspects of this essential ingredient. One particularly promising avenue is encapsulation.
Chemists have also found that combining retinol—or even more active retinal—with certain lipoproteins, glycoproteins, glycosaminoglycans (GAGs) and other natural plant-based amphiphilic compounds, can help overcome the challenge of permeating both water- and oil-based cellular barriers, as well as the issue of problematic irritation. In this case, multiple water- and lipid-soluble layers act as alternating keys, each allowing the transported ingredient—the retinoid—to pass deeper into the skin with less irritation.
Such encapsulation techniques have also been shown to reduce a retinoid’s trademark irritation. By minimizing the risk of adverse reaction, product developers can now increase retinoid concentration and, subsequently, product efficacy, without discomfort.