Surfactants and Their Functions in Hair Care
Some readers may remember that hair care before the 1980s was simpler with respect to the role of shampoos and the benefits they provided. Most brands essentially offered the consumer a dry, normal or greasy hair product variant in which the level and type of surfactant would be varied to deliver slightly different benefits.
Overall, it is safe to say that today’s formulation chemist faces significant challenges to create new commercially viable products that meet the challenge of superior performance and acceptable cost, along with compliance with emerging biodegradability and sustainability regulatory standards. On the plus side, the same chemist probably has access to more ingredients and technology options than ever before — to the extent that the range of choices can be overwhelming.
This article discusses surfactants and their roles in hair cleansing and care. It starts with a primer, considers traditional and modern ingredients, then looks to the future of these categories with specific examples from the industry.
Surfactants in Hair Care
As a review, surfactants, short for surface-active agents, are amphiphilic molecules, meaning they have both hydro-phobic (water-repelling) and hydrophilic (water-attracting) regions.1, 2 The primary role of surfactants is to help emulsify and solubilize oils and dirt on the hair and scalp. The hydrophobic tail of the surfactant binds to oils and grease, while the hydrophilic head allows the emulsified particles to be carried away by water during rinsing.
The role of surfactants in shampoos is multifaceted, as these ingredients play a crucial role in the cleaning, foaming and overall performance of the product. Surfactants also contribute to the formation of lather during washing, which while in and of itself does not necessarily enhance cleaning, is important to consumers, as they often associate a rich lather with effective cleansing.
Surfactants can also be used to control the viscosity of the shampoo formulation, which is essential for ensuring that it is thick enough such that when it is poured into the hand it does not run through the fingers. On the other hand, the shampoo must not be so thick that it is hard to apply and spread through the hair.
- Anionic: As most readers know, there are three main classes of surfactant used in shampoos. The first and primary surfactant in most shampoo formulations are anionic, examples of which are sodium lauryl sulfate (SLS) or ammonium lauryl sulfate (ALS). More often, the milder ethoxylated versions of these surfactants, e.g., sodium laureth sulfate — where an ethylene oxide chain is inserted between the anionic head group and the hydrophobic tail – are used in the majority of commercial shampoo formulations. The main role of anionic surfactants is to provide excellent foaming and cleaning properties.
- Nonionic: Nonionic surfactants such as cocamide MEA are often included as a secondary co-surfactant to enhance the mildness of the shampoo and reduce skin irritation.
- Amphoteric/zwitterionic: Alternatively, amphoteric or zwitterionic surfactants such as Cocamidopropyl betaine (CAPB) can also be used to improve the overall mildness of a formulation. In both cases, the nonionic or amphoteric surfactants interact with the primary anionic surfactant to lower the critical micellar concentration (CMC).
Processing and Substitutions
CAPB and CMEA, both are derived from coconut oil that is then reacted with dimethylaminopropylamine (DMAPA) and monoethanolamine (MEA), respectively. Both amines are usually derived from petrochemical sources.
In terms of cost effectively manufacturing shampoos, the use of laureth sulfate in combination with either CAPB or CMEA is the major formulation route.
Trends in Surfactants
While both ammonium and sodium laureth sulfate remain the dominant primary surfactants within the shampoo industry, clearly there are consumer concerns regarding the use of both petrochemical and palm-derived feedstocks in terms of their impact on the environment. Although most responsible manufacturers endeavor to source PKO from certified sustainable sources, nevertheless, there is pressure from consumers and organizations to move toward more environmentally friendly ingredients.
- Bio-based surfactants: For example, there is increasing demand for surfactants derived from robust and certified renewable resources, such as plant-based or bio-based surfactants. These ingredients aim to address environmental concerns and contribute to sustainable and eco-friendly formulations. Surfactants derived from sugars, becoming popular due to their natural origin and mildness.
- Mild surfactants: Formulators are also exploring surfactants that provide effective cleansing while being milder on the skin and hair. This trend is driven by consumer preferences for products that are gentle, especially for sensitive skin. Again, it is important to realize that many synthetic surfactants may offer mildness benefits.
- Biodegradability: Biodegradability is another critical factor in reducing the environmental impact of personal care products. As such, surfactants designed to break down more easily in the environment are gaining attention. Again, it is important to realize that a biodegradable surfactant is not necessarily sustainably sourced or even milder.
- Sulfate-free: Finally, due to extensive influencer comments regarding the use of sulfate-containing shampoos, products that are sulfate-free have become an increasingly important segment of the hair care market — although the precise technical and consumer benefits for hair are yet to be determined. Also, as alluded to above, a sulfate-free shampoo does not necessarily mean a milder product, compared with mainstream sulfate-containing shampoos.
Overall, it is important, when selecting a specific novel surfactant, that the formulator (and marketing partners) fully understand its relevant properties along with any trade-offs such as cost and performance.
The following section highlights a number of emerging commercially available bio-surfactants to illustrate the new benefits and potential claims they can offer. These bio-surfactants have gained attention from formulators for their surface-active properties, including wetting, emulsification and foaming, and are increasingly being used in shampoos for their mild and sustainable cleaning properties.
Notably, the foam produced may be different from the dense lather associated with synthetic surfactants such as sulfates. Another critical challenge associated with these new classes of surfactant is their production cost compared to traditional surfactants. Additionally, their sourcing and purification need to be carefully managed to ensure product consistency and quality.
Consumers prefer simplified routines with products offering multiple benefits. Advances in sulfate-free technology allow shampoos and conditioners to double as treatments, delivering nourishment and protection in one step. Such formulations align with consumer desires for convenience and high performance.
Natural Oils:
Natural oils that can be incorporated into formulations on their own or as combinations with other oils or emollients. Unlike silicones, these ingredients have rich backstories, supporting new compelling consumer stories and claims, which are summarized below. For example, Coconut oil is Known for its moisturizing properties, coconut oil can penetrate the hair shaft to nourish and condition the hair from within. It helps to reduce protein loss and strengthens the hair.
While these natural oils as an alternative to silicone offer promising solutions for reducing the environmental impact of hair care products, it is important to note that they may not provide identical performance to traditional silicones. Formulators may need to optimize formulations and adjust product claims to meet consumer expectations while leveraging the sustainability benefits of these biodegradable alternatives.
Conclusion:
Today’s formulation scientist faces an increasingly challenging and complex world in which the traditional palette of formulation ingredients to clean and care for hair becomes more restricted by regulators, is questioned by consumers and is under pressure from a range of NGOs. However, in response to this, technology companies and suppliers are creating ever more innovative ingredients that demonstrate either a significant improvement in ethical and sustainable sourcing and/or (bio)degradability profile, and overall carbon footprint to enable the creation of a new generation of shampoo and conditioner formulations with acceptable consumer performance.
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