ABOUT AUTHOR:
Vinay Kumar Singh
Chief Research Officer,
Paramount Cosmetics India,
Bangalore, Karnataka
vinay@parammount.com
We all love silky, shiny hair, and makeup that will stay put even when we work up a sweat. The synthetic ingredient that’s responsible for those results is usually silicone.
Silicones used in personal care applications are of diversified types, including cyclic, linear,or organo-functional polydimethylsiloxanes (PDMS), as well as silicone elastomer dispersions and resins. This wide range of molecules provides benefits that impact the performance of almost every type of beauty product, conferring attributes such as good spreading, film forming, wash-off resistance, skin feel, volatility and permeability.
I as a Chemist have been benefitted by use of Silicones many a times. In fact it has helped me formulate products that were really a challenge. No doubt, I advocate that Silicone Chemistry is future of Cosmetics.
Now as there have been few concerns particularly environmental, we; Chemists have to find solution to it to use Silicone without any fear or risk.
First introduced to beauty products in the 1950s, silicones are derived from a natural product called silica (basic sand), but undergo extensive chemical processing before being added to our beauty products.
The term silicone represents a large family of polymers that range from low viscosity fluids, to viscous gums, to cross-linked elastomers and hard resins. Their unique chemical and physical properties have made silicones important ingredients. It is best known for their aesthetic properties, these versatile materials improve the performance of many cosmetics, sunscreens and skin treatment products. They help deliver pigments and other particles to the skin, enhance protection by sunscreens and improve the stability of antiaging ingredients.
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.
There are numerous forms of silicones used in cosmetic products, particularly leave-on skincare products and all manner of hair-care products.
Silicones go by different names and are modified into numerous different formulas in order to perform the specific role expected of them like waterproofing, retaining moisture, adhering colour pigments, protecting our hair and imparting smoothness, and making the application of skincare products feel silky i.e. no tugging on the skin as it is spread on, and no oily, sticky feeling. They give our deodorants that velvety feel, allowing them to dry quickly, and they keep water-resistant sunscreens on our skin, even when we sweat or get wet.
In any product, all ingredients must be suspended in some base formula; some of the ingredients remain on the surface, some are absorbed. The intent is for the “actives” to get through. Moreover, the molecular structure of commonly used silicones makes it impossible for them to suffocate skin (not to mention skin doesn’t breathe). The unique molecular structure of silicones (large molecules with wide spaces between each molecule) allows them to form a permeable barrier and also explains why silicones rarely feel heavy or occlusive, although they offer protection against moisture loss. Interestingly, silicone has been shown to be helpful for offsetting dryness and flaking from common anti-acne active ingredients such as benzoyl peroxide and topical antibiotics. Also, silicones are sometimes used as fillers to improve the appearance of acne scars, which certainly wouldn’t be the case if silicone were a pore-clogging ingredient. Perhaps the most telling reason why silicones do not clog pores and cause acne (or blackheads) is because, from a chemistry standpoint, most silicones are volatile. That means their initially viscous (thick) texture evaporates quickly and does not penetrate the pore lining where acne is formed. Instead, they help ensure the even application of other ingredients and leave behind a silky, almost imperceptible feel that noticeably enhances skin’s texture and appearance; without irritation.
When it comes to our hair, silicones are conditioning workhorses. They are in most of shampoos, conditioners and treatments, and many styling products; the most common are dimethicone and cyclomethicone. They can repair signs of damage, fill in cracks and crevices in hair’s surfaces, return water resistance to damaged areas and prevent new damage from occurring.
Silicones have revolutionized the application and longevity of most makeup products, including foundation, eyeshadows, blushes, and liquid and pencil eyeliners.
Silicones are critical in many foundation formulations to give them more ‘spreadability’ and a luxurious, comfortable feel on skin. Silicones in liquid foundation help keep it flexible on the face and maintain a fresh, dewy look. Without their benefits, you could be left with dry powder on your face, which would be more likely to move into wrinkles or laugh lines.
Silicones are used to increase water resistance in a formula. This is particularly useful for sun-protection products, foundations and powders, especially those that make the claim of being water-resistant and waterproof. We also use them to resist transfer onto clothing.
Today’s “state of the art” liquid foundations often are formulated as w/o emulsions. Unlike conventional emulsions where the oily (water-insoluble) ingredients are dispersed as droplets in water, w/o emulsions are droplets of water dispersed in the other ingredients (e.g., oils or silicones). For a foundation that incorporates silicones with hydrophobic pigments, w/s emulsions are ideal vehicles. Such formulations have pleasant aesthetics, excellent spreading characteristics and optimize the film-forming properties of silicone resins.To prepare stable w/s emulsions, special polymeric silicone emulsifiers are required. These emulsifiers are made by grafting hydrophilic groups such as polyethers onto a dimethicone backbone. Common examples are PEG/PPG-18/18 dimethicone, bis-PEG/PPG-14/14 dimethicone and cetyl PEG/PPG-10/1 dimethicone. Silicone emulsifiers are typically liquid at RT and do not require waxes for emulsion stabilization, which creates a heavier feel. Formulators can explore new possibilities with silicone emulsifiers to respond to ongoing consumer demands for next-generation products with innovative textures, feel and improved performance.
Even the lips are not immune to silicone’s charms. It makes Lipstick last for hours. Another important property of silicones is their ability to act as a carrier for colour pigments. ‘If you want a high-performance, long-lasting lipstick, you need silicones.
Silicone resins such as trimethylsiloxysilicate and polymethylsilsesquioxane are film-formers that improve adhesion of pigments to the skin and transfer resistance. These resins are soluble in cyclomethicone and many other silicone fluids so they are easy to incorporate into cosmetic products. They can also be used in lipsticks to provide long-lasting color with greatly reduced transfer properties. In lip products, a high gloss film as well as attractive color is desirable. Phenyl silicones such as phenyl trimethicone are popular in this application. In addition to imparting gloss, phenyl silicones are more soluble in cosmetic waxes used in lipstick, a property that reduces the problem of syneresis, or bleeding of oil from the lipstick.
Silicone in hiding wrinkles: A better approach to concealing wrinkles is to apply materials with optical properties that allow them to reflect and scatter light in such a way as to reduce the visibility of wrinkles and other skin imperfections. This phenomenon is often referred to as the “soft focus” effect because it is similar to what happens when skin is photographed with a camera that is out of focus; skin features such as wrinkles are “blurred” by the effect of the treatment. Silicone fluids offer the same benefits for delivering soft focus particles to the skin. 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.
Skin Aging prevention: Many anti-aging skincare products use silicone elastomers. These are our friend when it comes to hiding the telltale signs of aging. They impart a soft, bouncy feel to the skin. They also optically help blur fine lines and wrinkles, so they have really advanced the anti-aging category.
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.
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.
A number of different polymers are used to increase the water resistance of sunscreen formulations. Many are acrylate polymers and silicone manufacturers have produced hybrid silicone-acrylate copolymers that offer the benefits of both. Other silicone film-formers such as silicone resins have been shown to increase the water resistance of sunscreens. Cyclomethicone is a popular carrier fluid for inorganic sunscreen dispersions, particularly when the sunscreen particles have a surface treatment to make them more hydrophobic. Silicone additives such as polyether-modified dimethicones are included to prevent re-agglomeration.
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Silicone in treatment for Aged Skin : Consumers with signs of aging want products that can repair the damage and return skin to a more youthful appearance. This is the realm of skin treatments that are designed to reverse the symptoms of aged skin. Such treatments represent a large part of the skin care market and utilize a variety of active ingredients. Some active ingredients have been used for many years, including tocopherol (vitamin E), retinol (vitamin A) and its derivatives, alpha-hydroxy acids (lactic acid, glycolic acid) and ingredients derived from plants. Advances in biochemistry over the past 5-10 years have produced antiaging ingredients designed to stimulate enzymes in the skin that produce structural proteins and other molecules present in younger skin. Many of these biochemical actives are peptides or peptide derivatives.
One property common to many antiaging actives is that they are fragile molecules and can lose their effectiveness via interaction with other ingredients in the formula. This problem has prompted the development of various delivery systems designed to protect the active ingredient in the formulation and make it available when the formulation is applied to the skin.
One of the simplest delivery systems that can effectively protect antiaging actives is an anhydrous formulation. This is because water and chemicals contained in the water (acids, bases, dissolved oxygen, and metal ions) are often responsible for the degradation of the actives. Although this issue is eliminated by removing water from the formulation, other problems are created. A formulation consisting entirely of oils and oil-soluble ingredients is usually perceived as greasy or oily by the consumer. Another problem is that most thickening agents used to control the consistency of the formulation must be used with water. So the challenge in an anhydrous formulation is to improve aesthetics and thicken the formulation so it is not too thin and does not separate over time.
Silicone fluids offer greatly improved aesthetics, and silicone elastomers provide thickening while further improving aesthetics.
Anhydrous skin treatment products based on silicones often are sold as small gelatin capsules that provide a single application when the capsule is broken. The protective effect of a silicone elastomer delivery system for certain actives that are soluble in silicone (e.g., retinyl palmitate) has been shown for conventional water-based formulations. The active is first combined with cyclomethicone and silicone elastomers, and this mixture is emulsified into the formulation. The affinity between the active and the silicone is apparently enough to keep the active in the silicone droplets and protected from degradation.
Claims that silicones in any form cause or worsen acne have not been substantiated in published research, nor have reports that silicones are irritating to or “suffocate” skin. Almost all of these claims are either myths or based on anecdotal evidence, which isn’t the best way to determine the safety or efficacy of any cosmetic ingredient. How do we know that silicones don’t suffocate skin? Because of their molecular properties they are at the same time porous and resistant to air. Think of silicones in a skincare formula like the covering of a tea bag. When you steep the tea bag in water the tea and all of its antioxidant properties are released.
Silicones are not natural ingredients. They are non-toxic and very friendly for skin. In the beauty world, Dimethicone is commonly used in primers and liquid foundations because it fills up imperfections in the skin and creates a smooth canvas for the foundation to go on. Just think of putting on makeup like painting a wall and you’ll get the general idea. If you use long wearing or waterproof makeup, chances are that it contains silicones too because silicone repels water and sweat. Silicones are also present in oil-control or mattifying products so you will notice that some products with silicone give a matte look to the skin. It is because it is holding the oil in under the layer of silicone so you don’t notice it so much.
In hair products, silicone is commonly found in hair serums and conditioners. It is what gives that shine to the hair and makes it feel smooth and soft. The principle is pretty much the same. The silicone coats the hair so it feels and looks soft and smooth
Although there’s no risk of real harm to your skin, the environmental risk, on the other hand, is cause of concern. These molecules are chemically inert, very stable, and that raises the question of their biodegradability; It seems to take them years to decompose… with all the pollution risks and risks of disturbing the ecosystem that result from that.
Siloxanes D4 (cyclotetrasiloxane), D5 (cyclopentasiloxane) and D6 (cyclohexasiloxane), in use since the 1970s, came under review in 2009 by Health Canada, because they had initially been found to meet the criteria for being considered bioaccumulative and having inherent toxicity to non-human organisms. However, ‘Health Canada has concluded that all three siloxanes [D4, D5 and D6] are safe for human health.According to Christelle Legault, media relations officer for Health Canada screening assessment considered human exposure from uses of D4 and D5 in personal care products and cosmetics, but the scientific evidence showed they did not pose a risk to human health at current levels of exposure.
Yves Lanctôt, an independent chemist in Quebec who helps new cosmetic companies develop their products and keeps abreast of current industry research, acknowledges that silicones are not natural ingredients. But, he says, ‘they are non-toxic and very friendly for skin. They are safe to use even around the eye area. There are no studies I’m aware of to show that silicones represent a danger to human skin.’
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