An affair to remember: Silicones and skincare. It started in the 1950s when dimethicone was used as an emollient, barrier former and “feel good” molecule. The 70s introduced a new type of fluid, volatile and low viscosity silicones, cyclomethicones, which act as solvent helping to deliver active ingredients to the skin. It was during the 80s when the love affair between skincare and silicones solidified with an increased demand for these molecules and the development of new versions such as non-ionic silicones (emulsifiers, foam stabilizers and wetting agents) and wax compatible silicones (ideal for lipsticks). Today, silicone elastomers and resins allow formulators to create elegant and light-weight products that hydrate the skin by forming a breathable barrier. In addition, silicones mattify the skin and fill in fine lines and wrinkles, smoothing texture, while providing a blurring effect.
Regardless if you like silicones or not, we have to acknowledge that they had taken the beauty industry by the horns becoming one of the most used ingredients in skincare, haircare and makeup (over 50% of the products launched in the past 10 years contain at least one type of silicone). Silicones, which are easily recognized by their names ending in col, cone, conol or zane; are synthetic, highly stable and large polymers made of repeating units that contain silicon [Si] and oxygen [O] as main atoms. Their backbones do not contain carbon [C] (this atom is only present in their side groups), therefore silicones are considered “inorganic” or “semi-organic” materials” (organic= [C] based). Due to their chemical composition and bonds, [Si]-[Si] bounds are stronger than [C]-[C] bonds, silicones are more resistant to heat than organic polymers. Thus, their side chains (attached to the backbone) are hydrophobic (repeal water) and almost non-reactive to other molecules. Silicones can be grouped in three different types: fluids, elastomers and resins depending on their cross-linking level. Fluid silicones are not cross-linked and therefore are linear and liquidy. Elastomer and resin silicones are both crosslinked resulting in more rigid nextworks. Elastomer silicones are ideal for sebum control as they absorb different types of oils providing a mattifying and smooth look that is powdery free. All silicones are great at improving the appearance, performance and feel of skincare products delivering a more luxurious texture to sunscreens, serums and moisturizers.
Silicones become popular just in time for the shifting in anti-aging age group leadership, or maybe it was the shift in leadership that triggered the development of silicones. Today, younger consumers are leading the beauty global market, searching for efficacious and elegant products to maintain a youthful appearance. Silicones are perfect to deliver what they are looking for, a smooth, velvety, non-greasy, non-oily application with the extra benefits of moisturization, increased spreadability and active ingredients enhanced penetration and protection.
As I stated in a previous post I love silicones and I am not afraid to use them. So, if silicones are so great why we are in the middle of a anti-silicone movement? Well, silicones are very popular synthetic molecules and we tend to have a bias in favor of natural molecules. In science, natural does not guarantee safety, lack of irritation or environmental friendliness. For example, essential oils are natural but irritate the skin and palm oil usage can have deleterious effects on the environment.
TOXICITY: Researchers have examined silicone toxicity measured by skin irritation, mutations (DNA alterations) and changes in the reproductive system determining that most of them are safe for human use (see below). It is important to remember that skin toxicity depends on factors such as concentration, exposure time, chemical composition of the formulation and the individual response. Dimethicone, one of the most commonly used silicones in skincare, is FDA approved for personal care and is considered safe to use. The Cosmetic Ingredient Review (CIR) had evaluated the scientific data available and concluded that this silicone is safe for cosmetic use. On the contrary, there are some indications that siloxanes (D4, D5 and D6) may pose a risk to the environment as they may accumulate in aquatic organisms, though they are considered safe for human health. In Europe, D4 had been classified as an endocrine disruptor.
OCCLUSIVENESS AND INHIBITION OF PENETRATION: Barriers formed by silicones are non-occlusive (this is the concept of “breathable barrier”) allowing the penetration of large molecules such as vitamin C and retinol while trapping water without interfering with natural functions of skin like perspiration. I would like to highlight that cetyl dimethicone uniquely forms a semi-permeable barrier and that C30-C45 alkyl methicone provide an occlusiveness similar to petrolatum. Some silicone films are not removed by water which people may think is bad (water resistance is not equal to occlusiveness). My recommendation when using products containing these silicones is to double cleanse (oil-based cleanser, followed by a water-based cleanser). Silicone acrylate copolymers are great for water resistant sunscreens and for products that are formulated for skin diseases in which active ingredients must be in contact with the skin for longer periods of time… as you can see for each skin need, there is a silicone we may use … the secret is to identify the one that works for you.
SKIN IRRITATION AND COMEDOGENICITY: Ingredient concentration and interaction with other components may determine if a final product is skin friendly (hypoallergenic) or non-comedogenic. Silicones are hypoallergenic and are not known to sensitize the skin; making them ideal for sensitive or compromised skin (disease or post-procedure). Allergic reactions to silicones are very rare especially if we consider how much silicones we use on a daily basis. Dimethicone is FDA-approved as skin protectant and is commonly used to decrease skin irritation. In subjects with eczema, silicones help to manage flakiness and skin cracking. Silicones lower AHA and retinol-linked irritation by improving skin hydration and helping products to spread evenly. Dimethicone also improves epidermal thickness and controls melanin production as shown by a study authored by Short et al (2007). Silicones, despite what people may think have either low-comedogenicity index or are non-comedogenic. Cyclomethicone has a standard rating of comedogenicity of 0 (completely non-comedogenic) while dimethicone has a rating of 1 (slightly comedogenic). On top of being non-comedogenic, silicones are excellent at offsetting dryness from acne-products that contains BPO or topical antibiotics. This is very important as skin dryness may increase the production of skin oils. Thus, silicones absorb sebum and mattify the skin, which visibly minimizes pores helping acne-prone skin.
FINAL REMARKS: All the products that I had conceptualized and co-designed that contain silicones passed the hypoallergenic test and are non-comedogenic. Silicones are not magic bullets, the important point here is to use the right silicone at the appropriate concentration to hit that sweet spot when you reach elegance, efficacy and safety. Silicones do not buildup on your skin as normal daily desquamation (shedding of cells) will remove the silicone from the upper layer too.
How do you know if you are exposing your skin to too much silicones? Well the products will ball up on your skin leading to pilling. When this happens is the time to review your skincare routine.
