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“Beauty in the flesh will continue to rule the world.” —Florenz Ziegfeld
Whatever high-tech actives or exotic botanicals a skin treatment product may contain, the delivery system is still an essential key to the product’s effectiveness. In most cases, traditional emulsions are used. These emulsions break apart on the skin as their water content evaporates, and the material left behind either lays on the surface or tries to penetrate the outer layers of the skin. The assumption underlying cosmeceuticals is that active ingredients will indeed penetrate and maintain or repair the deeper layers of the skin. Other approaches are possible, such as microemulsions or the use of polymeric emulsifiers. Liposomes are also used to deliver actives, and several products on the market now use liquid crystal systems as the carrier. These systems are promoted as superior to traditional emulsions for moisturization and nourishment of the intercellular matrix. What’s to be made of these claims?
Liquid crystals are all around you—take, for example, the numbers on digital watches and DVD players. Liquid crystals are an organized state of matter (thus crystal), but they can still flow (thus liquid), so they form a unique family of materials.
Liquid crystals can have different shapes. If they form flat sheets laying on each other, they are called lamellar. Liquid crystals in lamellar form result from the interaction of polar bilayers with water. These arrangements are classified as lyotropic because they rely on the action of a solvent. They can be destroyed by excess solvent or elevated temperatures. Soaps, detergents and polypeptides can form lyotropic liquid crystal systems—the slimy stuff that forms under a wet soap bar is an example.
A simple way to look at skin structure is as a brick-and-mortar model. The two ways a chemical can penetrate the skin are directly through the bricks (transcellular) or through the mortar (intercellular). A liquid crystal emulsion, like most cosmetic ingredients, will take the intercellular path.