Who doesn’t want silken, smooth, seemingly poreless skin and gleaming locks of hair? Smooth, poreless skin and shining hair are markers of youth and beauty. It is the promise in gleaming advertisements for skin and hair care products, but do not be fooled. Besides using photo editing software, there is one family of ingredients that is guaranteed to give the illusion of flawless skin and glossy hair, and that is silicones. Silicones are extremely useful in cosmetic formulations but they have also run into some controversy in recent years.
Silicon versus silicones
Silicon is an element, composed solely of silicon atoms. Like carbon, silicon is a Group IVA element; silicon (Si) is directly below carbon (C) in the periodic table of elements. This means silicon shares some similarities with carbon in terms of chemistry. For example, both silicon and carbon can form a maximum of 4 chemical bonds under normal circumstances. However, unlike carbon, silicon cannot form long chains with itself, but it can form stable long chains of silicon alternating with oxygen.
Silicones, also referred to as siloxanes, are a family of man-made compounds with alternating silicon (Si) and oxygen (O) atoms in a chain, forming the backbone of the polymer. Each silicon atom can carry two carbon-based groups.
Certain silicones can mimic some of the properties of the carbon-based oils and waxes, which are composed of long chains of carbon. A useful aspect of silicones is that they are relatively inert to the body’s biochemistry, and as a result, they exhibit low toxicity and low allergenic potential. Because of these characteristics, silicones are used in a wide variety of important applications ranging from medical/surgical devices and pharmaceuticals, to personal care products and cosmetics. In personal care products, they can form a water-resistant film on the skin that helps to seal in water. In water/oil emulsions that make up the base of most cosmetic products, they can be used to substitute all or part of the oil component.
There are literally hundreds of different silicone compounds, but they can be roughly categorized by the structure of their polymer backbone. The most common silicones in personal care products are:
Non-volatile silicones: dimethicone and related compounds
Dimethicone and related silicones have a straight chain backbone. These have an oily feeling, similar to mineral oil, and form a water-resistant film on hair and skin.
Volatile cyclic silicones: cyclopentasiloxane, cyclohexasiloxane
Cyclic silicones such as cyclopentasiloxane and cyclohexasiloxane are volatile, and are used in cosmetics and personal care products such as hair conditioners, styling products, and moisturizers that are meant to have a very light feel on the hair and skin. As they are volatile, they eventually evaporate off the skin and hair into the atmosphere.
Silicones have come in for some controversy recently. They were cited in the Suzuki Foundation’s “Dirty Dozen” list of suspect chemicals in beauty products (see my review of The Suzuki Foundation’s report here). Since that list came out, many cosmetic manufacturers, and particularly the green/eco brands, rushed to put out silicone-free products. In doing so, they missed reading the fine print of the report. It was only certain cyclic volatile silicones that were cited as being potentially problematic: cyclotetrasiloxane (also referred to as D4), cyclopentasiloxane (D5), cyclohexasiloxane (D6) and cyclomethicone (which is a mixture of two or more of the preceding compounds, usually D4 and D5). This conclusion was based on government reports from the European Union (EU), Environment Canada and California published between 2007-2009, all of which were based on inconclusive animal tests and data, and in which the report authors could only state potential risk, not probable risk.
The most recent report by the EU’s Scientific Committee on Consumer Safety, published in June 2010, concluded after a thorough review of the scientific research to date, that “cyclomethicone (D4, D5) does not pose a risk to human health when used in cosmetic products” [1]. This is an important conclusion, given that the EU has much stricter regulatory standards than either the US or Canada (a fact acknowledged by the Suzuki Foundation [2]). Unfortunately for the general public, this EU report was not reviewed in time for the publication of the Suzuki Foundation’s report (which came out in Oct. 2010). In the EU’s 2010 report, neither D4 or D5 were found to be carcinogenic or teratogenic, neither were found to be acutely toxic, and they do not appear to bioaccumulate in the body to a significant degree. Although the report was limited to D4 and D5, the authors noted that D6 may be present in either D4 or cyclomethicone. Due to their structural similarity, D6 likely has a low toxicity profile, similar to D4 and D5. Furthermore, these silicones do not seem to accumulate to any significant degree in the environment; instead, they are eventually degraded to silica, water and carbon dioxide.
In spite of all the undue suspicion surrounding cyclic volatile silicones, one fact is clear: silicones have made possible huge advances in medical and pharmaceutical technology, as well as cosmetic formulation technology. With regards to cosmetics and skin care, the use of silicones to replace some or all the oil component in water/oil emulsions allows the creation of advanced hair and skin conditioners that help retain moisture while still being low-oil or oil-free. As a result, you can get glossy hair without greasiness and you can get oil-free moisturizers that help the skin retain water without adding oils that can cause pimples.
The oil-free and low-oil skin care products, made possible with silicones, are a boon for people trying to deal with adult acne. This is the type of acne that crops up during the 30s onwards, due to stress and hormonal changes. Most acne skin care products are formulated with teenage skin in mind, skin that is more resilient to harsh treatment. Older skin types are more fragile and prone to scarring and wrinkling. The key to caring for problem-prone ageing skin is to use a lightweight moisturizer with low (or no) oil content, that relies instead on water and non-oily humectants to add moisture: such a formulation allows the skin to retain water, keeping wrinkles at bay, while also bolstering the barrier function of the skin and preventing over-production of sebum that can lead to breakouts. Earlier versions of oil-free moisturizers tended to contain too much silicone, forming an uncomfortable film on the skin that did not actually provide any moisturizing benefit. Newer, more advanced formulations contain more water and humectants lower silicone content, so they feel more natural on the skin.
Silicones can also be used as part of the base in cosmetics as well as hair car products. Some notable examples include foundation primers, BB creams and lightweight liquid foundations and hair styling products. In foundation primers and BB creams, non-volatile silicones fill in skin imperfections, creating the illusion of smooth skin. In lightweight liquid foundations, volatile silicones are often used as the base: once applied, the silicone evaporates, leaving behind a layer of pigment. Silicones are also found in many hair care products, particularly smoothing serums and conditioners. Once applied to the hair, the silicones form a film that smoothes over rough parts of the hair cuticle, thus making hair appear shiny.
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References:
- “Opinion on Cyclomethicone, Octamethylcyclotetrasiloxane (cyclotetrasiloxane, D4) and decamethylcyclopentasiloxane (cyclopentasiloxane, D6).” Scientific Committee on Consumer Safety. European Commission, Directorate General for Health & Consumers. SCCS/1241/10. 22 June 2010.
- “Backgrounder: The “Dirty Dozen” ingredients investigated in the David Suzuki Foundation survey of chemicals in cosmetics.” The David Suzuki Foundation. October 2010.