How to choose an emulsifier for formulation: why HLB matching isn’t the whole story

On this page

• Emulsifier selection goes far beyond basic function
• What is HLB, and how do you use it effectively in cosmetics?
  • Case Study: Polysorbates
• Why do emulsifiers with the same HLB perform differently?
• How does the emulsifier choice shape formula feel?
  • Rich & Thick sensory with Brij™ S2 and Brij™ S721
  • Nourishing, Smooth, and Creamy Textures
  • Selecting Emulsifiers by Target Application & Sensory Feel
• Emulsifier selection is a strategy, not just a function

Emulsifier selection goes far beyond basic function

Emulsifiers are the unsung heroes of personal care products. While combining oil and water phases requires solid technical knowledge, selecting the right emulsifier also shapes the overall consumer experience.

At their core, these amphiphilic agents blend immiscible phases like oil and water by coating dispersed droplets to prevent separation. Yet beyond basic stability, emulsifiers help shape the tactile experience – determining whether a formula feels weightless, cushiony, rich, or velvety upon application.

The Hydrophilic-Lipophilic Balance (HLB) scale (0–20) helps predict emulsion types and texture profiles. However, emulsifiers with the same HLB value are not automatically interchangeable.

Ingredients at the same spot on the scale often differ in chemical structure, melting point, and physical form. To address these variations, selecting the right ingredient requires a structured three-step method:

1. Match the required HLB: Calculate the exact HLB needed for the oil phase to ensure proper blending and stability.
2. Filter by Technical Performance: Review chemical compatibility to keep the formula stable and mild under key processing, regulatory, and formulation conditions:
1. Thermal stability and temperature range tolerance
2. Cold vs. hot processing capabilities
3. Global compliance and clean-beauty certifications
3. Select by Sensory Signature: Refine the options to deliver the exact skin feel – from light fluids to rich creams – that consumers prefer.

Continue reading to explore the selection process of emulsifiers and multiple ingredient solutions from Croda Beauty, offering practical guidance on how to curate the ideal match for any formulation.

What is HLB, and how do you use it effectively in cosmetics?

The HLB value reveals whether an emulsifier is hydrophilic (water-loving) or lipophilic (oil-loving), directly steering product architecture and tactile feedback:

• Oil-in-Water (O/W) Systems: Refreshing, lightweight, rinse off, which rely on high-HLB emulsifiers.
• Water-in-Oil (W/O) Systems: Rich, protective barrier formulations, that depend on low-HLB emulsifiers.

When a single ingredient cannot provide both required stability and desired texture, creating a custom HLB blend offers an effective solution.

Combining low- and high-HLB ingredients can match the exact required HLB of the oil phase. This forms a protective layer around oil droplets to prevent separation. For example, to reach a target HLB of 10, combining Croda’s Brij™ S2 (HLB 4.9) and Brij™ S721 (HLB 15.5) in roughly a 52:48 ratio provides strong stability and a soft, smooth texture.

At its core, an emulsifier's HLB reflects the exact ratio of its hydrophilic head to lipophilic tail. For non-ionic surfactants, this balance is calculated using standard formulas based on relative molecular weights, translating molecular structure directly into predictable functional behavior.

Case Study: Polysorbates

The polysorbate family illustrates this concept clearly. While sharing the same water-loving head group, performance shifts according to the length of the oil-loving fatty acid tail:

• Tween™ 20: A compact lauric acid tail yields a high HLB of 16.7, making it an exceptional solubilizer for crystal-clear aqueous systems.
• Tween™ 60: A longer 18-carbon stearic tail increases oil weight, lowering the HLB to 14.9 – making it a standard choice for classic lotions and creams.

As the polysorbate series shows, HLB serves as a reliable mathematical guide to surfactant behavior. By adjusting chain lengths and head-group structure, formulators can fine-tune stability and performance. However, relying on HLB alone is not enough when designing high-performing formulations.

Why do emulsifiers with the same HLB perform differently?

Reaching a target HLB is only the first step. The HLB value serves as a helpful guide, but it does not fully predict how an emulsifier behaves in a complete formula. Two ingredients can share the same number yet act differently in practice due to structural and physical variations. Consequently, relying on HLB alone cannot guarantee identical performance.

To choose an emulsifier that performs – and delivers the desired skin feel – evaluate candidate options against these essential performance checks:

1. Oil Compatibility & Inclusion Levels
   • Polarity Matching: Match emulsifier structures with oil phase polarity (e.g., polar plant oils vs. non-polar silicones and hydrocarbons).
   • High Oil Content: Formulations with high oil levels (>30%) require strong structural networks beyond simple HLB matching.
   • Lipid & Wax Stabilization: Prevent unwanted crystallization or liquid separation when using heavy plant butters or waxes.
2. Co-Surfactants & Rheology Support
   • Liquid Crystal Networks: Combine with fatty alcohols (such as Cetearyl Alcohol) to build gel structures that lock in moisture and improve hydration.
   • Charge Stabilization: Add small amounts of secondary emulsifiers (such as Sodium Stearoyl Glutamate) to increase repulsion between oil droplets and prevent separation.
   • Thickener Compatibility: Ensure compatibility with rheology modifiers (such as Carbomers or Xanthan Gum) to prevent loss of texture.
3. pH Robustness & Electrolyte Tolerance
   • Chemical Stability: Use strong ether or glucoside bonds for extreme pH environments; ester bonds may break down outside pH 4.5–8.0.
   • Salt Tolerance: Use alkyl polyglucosides (APGs) or ether-based systems in high-active formulas to prevent breakdown from salts.
4. Texture, Viscosity & Sensory
   • Viscosity Build: Check if the main emulsifier builds thickness on its own or needs extra thickening ingredients.
   • Particle Suspension: Maintain sufficient structural support to keep mineral UV filters or color pigments evenly suspended.
   • Sensory Profile: Design application textures ranging from fresh, fast-absorbing gels to rich, smooth creams.
5. Further requirements a formulation brief might have
   • Processing Energy: Select energy-efficient cold-process systems or hot-process methods required for high-melting waxes.
   • Skin Compatibility: Select mild emulsifiers for sensitive skin formulations and leave-on products.
   • Clean Standards: Align emulsifier selection with COSMOS standards, RSPO palm traceability, or other product requirements.
   
   

How does the emulsifier choice shape formula feel?

While technical metrics like HLB and stability testing confirm that a formula works, sensory properties determine how consumers experience the product. Formulators carefully select emulsifiers to achieve specific textures – from light, fast-absorbing fluids to rich night creams.

Rich & Thick sensory with Brij™ S2 and Brij™ S721

To build a thicker body, pairing Brij™ S2 (Steareth-2) and Brij™ S721 (Steareth-21) offers full control over texture. As discussed in Section 2, blending low- and high-HLB emulsifiers matches the exact required HLB of the oil phase to form a stable structure. Beyond ensuring physical stability, this combination provides rich sensory and a comfortable skin feel across lotions and creams. 

Nourishing, Smooth, and Creamy Textures

For natural formulations, NatraGem™ EW is a self-emulsifying base that adds thickness to a system. It works across pourable lotions and high-viscosity body creams while being non-whitening during application and providing SPF boosting.

For classic, thick O/W creams, Arlacel™ LC builds hydrosome-based liquid crystal networks. This prolongs skin hydration and offers controlled release of actives

Selecting Emulsifiers by Target Application & Sensory Feel