Emulsifiers are key ingredients in formulation, as they enable the combination of two phases that would naturally tend to separate, such as water and oil. Their main function is to reduce <\/strong>the interfacial tension between both liquids, allowing them to mix uniformly and remain stable over time. This is possible due to their amphiphilic nature<\/strong>: within the same molecule, there is a lipophilic group (affinity for oils) and a hydrophilic group (affinity for water) (Figure 1). <\/p>\n<\/div>\n When incorporated into a system, emulsifiers spontaneously migrate to the oil\u2013water interface, where they orient themselves so that each end interacts with its compatible phase. This phenomenon reduces the free energy associated with the interface and stabilizes the dispersion. <\/p>\n\n Furthermore, above a critical concentration, many emulsifier molecules tend to self-organize into micelles: structures in which the hydrophobic groups are protected inside, surrounded by a hydrophilic \u201cshield\u201d in contact with water. <\/p>\n\n This dynamic equilibrium between free molecules and micelles contributes to maintaining system stability and controlling droplet size<\/strong>. The smaller the droplet diameter and the larger the interfacial area, the greater the amount of emulsifier required to cover it. Otherwise, the system tends to minimize the exposed surface, promoting coalescence phenomena and eventual phase separation. <\/p>\n\n Depending on which phase acts as the continuous phase and which as the dispersed phase, different types of emulsions can be distinguished:<\/p>\n\n The selection of the emulsion type directly determines the required emulsifier. Formulating a lightweight O\/W system is not the same as developing a water-resistant W\/O emulsion.<\/p>\n\n The chemistry of an emulsifier defines its solubility, compatibility and function within cosmetic formulations. <\/p>\n\n Based on their charge, emulsifiers can be classified as follows:<\/p>\n\n The HLB <\/strong>(Hydrophilic-Lipophilic Balance) concept remains a classical and widely used tool to guide emulsifier selection.<\/p>\n\n <\/p>\n\n In practice, formulators do not rely on a single emulsifier but instead combine surfactants with different HLB values.<\/strong> For example, it is common to combine a highly hydrophilic surfactant (HLB 16\u201320) with one of intermediate HLB (9\u201315) and a more lipophilic one (<8), adjusting the proportions to obtain an emulsifying system capable of stabilizing oils with different polarities. This approach allows modulation of viscosity, improved tolerance to temperature changes, and the achievement of more robust emulsions. <\/p>\n\n The combination of fatty alcohols with non-ionic emulsifiers is also a common strategy. For instance, blends such as Cetearyl Alcohol<\/em> and Cetearyl Glucoside act as self-emulsifying O\/W systems, providing high stability and a pleasant creamy texture in facial and body creams. <\/p>\n\n The origin of the emulsifier defines both its technical profile and its market perception:<\/p>\n\n The Hydrophilic\u2013Lipophilic Balance (HLB)<\/strong> system was developed by Griffin in the mid-20th century to facilitate emulsifier selection. It is a numerical index (ranging from 0 to 20 in the original method)<\/strong> that reflects the relative affinity of a surfactant for water (hydrophilic) or oils (lipophilic). <\/p>\n\n <\/p>\n\n Subsequently, Davies proposed an extension of the system by considering the contribution of different functional groups within the molecule, allowing the scale to be extended up to values of 40 in some cases (especially for ionic surfactants).<\/p>\n\n In cosmetics, it is important to distinguish between:<\/p>\n\n The basic principle is straightforward: oils with a low required HLB need emulsifiers with low HLB, and vice versa<\/strong>. If there is a mismatch, the system loses stability, leading to phase separation or undesirable textures.<\/p>\n\n Although it is possible to use a single emulsifier that matches the required HLB, in practice it is often more effective to combine a high-HLB emulsifier with a low-HLB one.<\/strong><\/p>\n\n The formulation of emulsions in cosmetics requires consideration of both process parameters and ingredient compatibility. Emulsifiers do not act in isolation: their effectiveness depends on the balance between phases, the order of addition and the emulsification conditions. <\/p>\n\n The first step in designing an emulsion is to define the balance between the aqueous phase and the oil phase. In both cases, the ratio between water and oil not only determines the sensory profile but also the final viscosity and overall robustness of the emulsion. Therefore, this balance must always be considered together with emulsifier selection and the manufacturing process. <\/p>\n\n Stability depends on working at appropriate temperatures<\/p>\n\n In practice, it is common to combine:<\/p>\n\n The synergy between both defines the emulsion\u2019s resistance to variations in pH, temperature and storage conditions.<\/p>\n\n In W\/O emulsions, in addition to primary emulsifiers, co-emulsifiers such as Glyceryl Caprylate can play a dual role: increasing system viscosity and improving resistance to coalescence, while also providing an emollient touch that enhances the final sensory profile of the product.<\/p>\n\n The selection of the emulsifying system must also be adapted to:<\/p>\n\n <\/p>\n\n It is important to understand that an emulsion is not a naturally stable system, but a transient state that can be maintained for months or years thanks to emulsifiers.<\/strong> These ingredients act as a barrier that delays phase separation, although they cannot completely prevent it.<\/strong><\/p>\n\n <\/p>\n\n Figure 3<\/strong> helps to visualize this concept. In the initial state, with the phases separated, the system is at a low free energy level (G\u2080<\/strong>). Upon applying energy during emulsification (stirring, homogenization), the system transitions to a metastable state (G\u2081<\/strong>), where water and oil are dispersed as droplets. Meanwhile, dispersed droplets are in constant motion due to thermal agitation or gravity, colliding with one another. Over time, these interactions promote destabilization processes, which manifest through different mechanisms: <\/p>\n\n![\"\"](\"https:\/\/ismaelquesada-personalcare.com\/wp-content\/uploads\/2025\/08\/Captura-de-pantalla-2025-08-24-a-las-15.45.23.png\" "\\"Schematic")
2. Types of Emulsions in Cosmetics<\/h2>\n\n
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Classification and Selection of Emulsifiers<\/strong><\/h2>\n\n
According to ionic charge<\/strong><\/h3>\n\n
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According to Hydrophilic-Lipophilic Balance (HLB)<\/strong><\/h3>\n\n
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According to Origin <\/strong><\/h3>\n\n
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3. Required HLB and Stability<\/strong><\/strong><\/h2>\n\n
What is HLB?<\/strong><\/h3>\n\n
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HLB<\/strong><\/td> Water Solubility<\/strong><\/td> Application<\/strong><\/td><\/tr> 1,5 – 3<\/td> No dispersion in water<\/td> Antifoaming agent<\/td><\/tr> 3 – 6<\/td> Poor dispersion in water<\/td> W\/O emulsifier<\/td><\/tr> 7 – 9<\/td> Milky dispersions<\/td> Humectant agent<\/td><\/tr> 10 – 18<\/td> Stable milky dispersions<\/td> O\/W emulsifier<\/td><\/tr> 13 – 15<\/td> Nearly transparent dispersions<\/td> Detergent<\/td><\/tr> > 15<\/td> Clear solutions<\/td> Solubilizer<\/td><\/tr><\/tbody><\/table> Real HLB vs Required HLB<\/strong><\/h3>\n\n
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Emulsifier Blending Strategy<\/strong><\/h3>\n\n
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4. Formulation with Emulsifiers<\/strong><\/h2>\n\n
Oil\/Water Phase Ratio<\/strong><\/h3>\n\n
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Emulsification Temperature <\/strong><\/h3>\n\n
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Primary and Secondary Emulsifiers<\/strong><\/h3>\n\n
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Compatibility with Actives and Desired Texture<\/strong><\/strong><\/h3>\n\n
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6. Emulsion Destabilization Factors<\/strong><\/h2>\n\n
![\"\"](\"https:\/\/ismaelquesada-personalcare.com\/wp-content\/uploads\/2025\/08\/Captura-de-pantalla-2025-08-24-a-las-14.18.08-1.png\" "\\"Metastable")
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