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One of the dominant trends in today’s dynamic skin care market is the quest for products that effectively prevent and treat aging skin. The importance of antiaging benefits is driven by demographics and the desire of most consumers to maintain a youthful appearance. The population in the leading personal care markets including the United States, Western Europe and Japan, is shifting toward older consumers as birthrates decline. At the same time, the rise in living standards in emerging markets allows aging consumers to purchase more sophisticated skin products that incorporate the latest developments in antiaging technology. The global skin care industry has responded by developing products intended to prevent premature aging, reverse specific aspects of aged skin and improve the appearance of skin.
Dimethicone – the Silicone Foundation for Skin Care
Silicones have a long history of use in skin care products, beginning in the 1950s. The first applications involved basic silicone fluids (INCI: Dimethicone). These linear polymers are liquid over a wide range of molecular weights. Dimethicones remain important for their emollient properties and their ability to improve the skin feel of many types of skin care formulations. In the late 1970s, another important class of silicones was introduced to the industry. Cyclomethicones are volatile, low-viscosity silicone fluids that act as cosmetic solvents. They are particularly suited for use with other silicones and as delivery vehicles for a variety of active ingredients.
Starting in the 1980s, the increasing popularity of silicones in skin care applications prompted silicone manufacturers to develop a variety of new materials, which led to even broader use. Many of the new silicones were derivatives of dimethicones, where specific functional groups were added to the backbone of the silicone polymer. For example, grafting hydrophilic polyethylene oxide chains to the dimethicone backbone produces non-ionic silicone surfactants that are useful as emulsifiers, foam stabilizers and wetting agents. Another family of silicones was created by introducing phenyl groups onto the silicone backbone to produce fluids with a higher refractive index and increased compatibility with cosmetic waxes. These phenyl silicones are useful for color cosmetics such as lipsticks, where the goal is to produce a high gloss coating on the lips.
One of the newest and most rapidly growing classes of silicones used in skin care applications is silicone elastomers, which are made by cross-linking dimethicone polymers to produce elastomeric solids that have properties quite different from dimethicone fluids. As the degree of cross-linking increases, the silicone network becomes more rigid. Although they are produced by a different process, silicone resins can be thought of as representing the most extreme examples of cross-linked silicone polymers. Silicone resins have a tight, three-dimensional structure that results in rigid materials that can form hard, durable films. Figure 1 illustrates variations in polydimethylsiloxane morphology based on increasing molecular weight and cross-linking.
Silicone Applications in Cosmetics
The signs of skin aging include a number of undesirable changes in its appearance, such as the development of wrinkles, loss of elasticity and uneven pigmentation. One of the most popular approaches used by skin care product manufacturers to address these problems is to develop cosmetics, which are products that temporarily improve skin appearance. Cosmetic products represent a large fraction of the skin care market because they work. They essentially provide instant gratification because consumers notice an improvement as soon as the product is applied. This is in contrast to products intended to provide a therapeutic effect, which may require 6 to12 weeks before improvement becomes apparent.