Silicones' Benefits in Antiaging Skin Care

By: Michael S. Starch, Dow Corning Corp.

Posted: November 13, 2008

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The most effective soft focus materials are various transparent particles. The transparency allows the skin color to pass through the particles, giving a more natural skin appearance. Optical effects are influenced by the size, shape, and refractive index of the particles. Spherical particles are popular because they spread well, have a pleasant feel and act as tiny lenses that bend light to create the soft focus effect. Silicone fluids offer the same benefits for delivering soft focus particles to the skin as they do for pigment particles. The refractive index of the silicone can be adjusted by choosing a dimethicone fluid or a phenyl silicone that has a higher refractive index. Spherical silicone elastomer and silicone resin particles are gaining in popularity for face care products. These are useful for soft focus applications because they have a different refractive index than organic cosmetic oils. Light scattering typically increases when the oils and the particles in the film have different refractive indexes. Apart from their aesthetic and optical properties, silicone elastomer particles offer the added benefit of absorbing sebum.

Prevention of Skin Aging
Many skin care products make claims for the prevention of skin aging by protecting the skin against the damaging effects of pollution, cigarette smoke, free radicals and other environmental insults. These claims have some scientific basis, but by far the most important factor in skin aging is exposure to the ultraviolet radiation in sunlight. Countless studies have shown that ultraviolet radiation causes cumulative skin damage that leads to loss of elasticity, uneven pigmentation and other signs of aged skin. The most effective prevention is regular use of sunscreen, which protects the skin against exposure to ultraviolet radiation.

Recognition of this fact has led to rapid expansion of products that contain sunscreen ingredients, particularly for use on the face and other areas of the body that are exposed to the sun on a daily basis. These active ingredients fall into two broad categories: organic and inorganic. Organic sunscreens are usually oily liquids that are added to a formulation in concentrations ranging from 3%-15%. Inorganic sunscreens consist of particles of titanium dioxide or zinc oxide that are used alone or in combination with organic sunscreens. When used alone, inorganic sunscreen concentrations range from about 10% to as high as 25%. When used to supplement the protection form organic sunscreens, inorganic sunscreens are typically included at 2-8%.

For both organic and inorganic sunscreens, the goal is a formulation that delivers the sunscreens in a uniform film to maximize protection against ultraviolet radiation. The film should remain uniform over time and help keep the sunscreens in place so they are not removed when the skin is brushed against other surfaces. For sunscreen products intended for use at the beach or during exercise, the sunscreen film must also be resistant to wash-off.

Silicone fluids are widely used in sunscreen formulations because of their ability to reduce the oily and sticky skin feel associated with high levels of organic sunscreen oils. Silicone fluids with phenyl groups have better solubility in sunscreen oils and this can increase the effectiveness of the sunscreen, presumably by producing a more uniform film on the skin. Silicone waxes in which long-chain alkyl groups have been grafted onto the silicone backbone have been shown to increase the protective effect of sunscreens. These silicone waxes are solids that affect the rheology of the formulation; they increase the viscosity of the sunscreen film on the skin so that it has a greater tendency to stay in place.