Silicones have been widely used in the cosmetic industry for decades. They are exceptionally versatile and impart multifaceted benefits across a wide range of beauty and personal care products. Not all silicones have been created equal, however, and some of these materials are now limited by regulatory restrictions on their use. Due to an increasing focus on their toxicological and environmental impact, consumers are now gravitating towards natural, safe, and sustainable alternatives. This article provides an overview on how silicones have shaped the hair care industry and the continuous research necessary to find innovative and environmentally friendly alternatives to silicones.
Influence of Silicones in the Hair Care Industry
Silicones have been important ingredients in hair care products since the 1950’s. Silicones or silicone derivatives are widely used in shampoos, conditioners, colorants, or styling products where they act as either emollients, humectants, film formers, antifoaming, anti-static, or binding agents . These materials range from basic cyclic or linear polydimethylsiloxane (PDMS) to polyether-and amino-based fluids and silicone resins . All silicones have a natural origin (silica), but synthetic processes are used to create the plethora of silicone ingredients used in cosmetics .
Linear PDMS, also known as dimethicone, is available in a range of molecular weights and viscosities and is most used in hair care applications. They provide excellent conditioning and performance which increases with higher viscosity. Use of dimethicone reduces combing forces, provides great sensory benefits like gliding, and adds suppleness to hair.
Phenyl trimethicone is also based on linear PDMS with the addition of phenyl groups . This combination results in a higher refractive index that effectively coats the hair enhancing its shine and leaving hair soft. PDMS polymers are also highly water resistant which makes them effective agents in reducing tackiness of the formulations.
Cyclic polydimethylsiloxane (cyclic PDMS) or cyclomethicones fluids are characterized by ring structures typically containing three to six groups per ring . These fluids decrease combing forces by reducing friction and surface energy . Due to their volatility and fast spreading properties, they provide transient gloss to hair, leaving hair weightless and without any build-up. Cyclomethicones are more compatible with a wider range of ingredients versus linear PDMS.
Silicone gum/fluid blends provide a high level of substantive conditioning and frizz control while imparting a soft and lubricious feel . There are silicones that are modified, like amodimethicones (amine-functionalized silicones) or alkylmethicones (replacing methyl groups on PDMs with alkyl chains) which are widely used in hair care applications as well. Amodimethicones impart specific benefits like color protection, heat protection, repair, reduced flyways, and deep conditioning.
The above-mentioned silicones are non-water soluble, whereas silicone polyethers are a family of water and/or alcohol soluble materials commonly used in shampoo formulations. They provide light to medium conditioning. In addition to acting as emulsifiers or co-emulsifiers, they can be used as resin modifiers to aid curl retention .
Moving Away from Silicones
While silicones have been highly effective hair care ingredients providing both functional and enhanced sensorial benefits, there is a movement away from their use due to a variety of reasons. There are long-term effects of silicone such as causing build-up, greasiness, and scalp accumulation . Furthermore, concerns have been raised about their toxicity and effects on the environment.
The Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) assessed the potential environmental effect of cyclic silicones: cyclotetrasiloxane (D4) and cyclopentasiloxane (D5). Based on the evaluation, D4 meets the criteria for identification as a persistent, bio accumulative and toxic (PBT), very persistent, very bioaccumulative (vPvB) substance and D5 meets the criteria for a vPvB substance . After January 31st, 2020, the concentration of D4/D5 in rinse-off cosmetic products placed on the market should be less than 0.1% by weight of either substance. This has now been amended to include cyclohexasiloxane (D6) and is expected to be further restricted to include leave-on products .
Linear silicones are also not completely in the clear. They are suspected to be an environmental toxin and to be bioaccumulative. Dimethicone, Dimethicone Copolymer, Polysilicone-15 and other silicones are commonly considered to be microplastics [8,9]. In addition to being non-biodegradable, silicone oils also have an impact on the environment due to their industrial production process which has a high carbon footprint .
High performance, Natural and Sustainable Solutions
According to Mintel’s GNPD, between 2016 and 2021 the incidence of “silicone-free” claims for hair care products increased by over 200%. With regulations to control the usage of silicones in hair care products and a growing emphasis on naturality and sustainability, companies are looking for ingredients that serve as silicone alternatives. There is a huge focus on developing efficient and innovative ingredients that offer similar or better functional performance and with a better sensorial profile than silicones. A few ingredient solutions currently offered are highlighted below:
C13-C15 Alkane (plant-derived) is a sustainable natural silicone replacement developed via the fermentation of renewable sugar and grown sustainably without irrigation. This ingredient meets the performance of dimethicone in frizz reduction and color protection. It also matches the performance of amodimethicone in terms of wet/dry combability and provides an excellent sensorial profile. Ethyl Macadamiate is another silicone alternative of macadamia esters. It is biodegradable and provides the same silky, smooth after feel as cyclopentasiloxane . A highly viscous, hydrogenated polyfarnesene presents interesting properties to replace Dimethiconol-based blends .
A prime function of silicones is to act as emollients. A vegetable emollient that is readily biodegradable and reduces significant carbon footprint is a perfect ally to protect hair from repeated mechanical stress and perform superior to cyclopentasiloxane . An example is Hydrogenated Olive Oil which is an unsaponifiable squalene from olive oil and hydrogenated castor oil. It is yet another emollient offering to replace silicone and mineral oils that has great application in anti-frizz haircare products .
Reduced Silicone Solutions
It is not necessary to exclude all silicone products; cyclic free or synthetic silicones that meet REACH requirements can still be used as alternative solutions. Using low viscosity dimethicone and a mixture of C13-C14 isoparaffin can be considered as a replacement for cyclomethicones delivering a similar sensory profile . Use of terminal hydroxy amino-modified silicone (THA) chemistry provides long-lasting conditioning and protects hair against breakage . As for synthetic offerings, combining quaternary conditioning properties of cetrimonium chloride with a carboxylated silicone provides thermal protection and enhances the manageability of hair, while a complex of cetrimonium chloride with a water-soluble silicone provides great hair care benefits in different formats . A combination of natural oils and a synthetic polymer can enhance and extend the benefits of natural oils to smooth and restore damaged hair and protect and reduce hair damage from different grooming regimens .
The industry also offers some unique solutions like quat-free polymeric conditioning additives that can provide multi-functional benefits to hair which are ideal for amodimethicone free formulations. Lastly, to reduce the carbon footprint, manufacturers are cutting down the high use of energy to produce dimethicones of various viscosities by using methanol obtained from biomass instead of fossil fuels .
Using Digital Tools to Source Ingredients
In the quest for clean and sustainable ingredients, Artificial Intelligence (AI) is playing a critical role in research and development. Machine learning is a powerful tool that can collect large amounts of data and provide detailed information about ingredient sourcing . AI will be further integrated to explore unmet needs and help screen and identify innovative ingredients for various applications. Companies are also developing apps, using QR codes to trace ingredients, and promote ingredient transparency by providing origin and sustainable properties .
Over the last decade, there has been a strong shift in consumer product preferences with emphasis on personal wellbeing and the environment. The cosmetic industry has made great progress in offering many eco-friendly, clean, and sustainable solutions not only to replace silicones but also other ingredients that are currently being challenged. Companies are tasked to continue their efforts in developing eco-friendly and sustainable products that are highly effective in functional and sensorial performance to meet consumer needs.
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Mythili Nori has worked in the Personal Care industry for over a decade. Her expertise is in Product Claim Substantiation and Data Science. In her current role at BASF, she is responsible for Physical Claim Substantiation & Sensory testing for Hair & Skin Care. Prior to joining BASF, she spent 5 years at TRI/Princeton as a Senior Research Associate, supporting claim substantiation and fundamental research activities for textile and hair surfaces. She earned a Bachelor of Technology in Chemical Engineering from India and received Master of Science in Chemical Engineering at North Carolina Agriculture & Technical State University focusing on purification of drinking water.