Choosing the Right Emulsifier

You can’t make a lotion, cream, or serum without creating an emulsion. And, at the heart of any emulsion is the emulsifier, a raw material that lets you combine ingredients that normally want nothing to do with each other.

Choosing an emulsifier isn’t just about picking one from a dropdown menu. You need to understand how they work, what their limitations are, and when to use oil-in-water vs. water-in-oil systems.

What Is an Emulsion?

An emulsion is a mixture of two immiscible liquids (usually oil and water) where one is dispersed in the other in the form of small droplets. Since oil and water naturally repel each other, they need help staying mixed. That’s where emulsifiers come in.

What Does an Emulsifier Do?

An emulsifier is a surface-active molecule with:

• A hydrophilic (water-loving) head

• A lipophilic (oil-loving) tail

This dual nature allows the emulsifier to sit at the oil-water interface, reducing surface tension and forming a physical barrier that keeps droplets from coalescing (merging). The result? A stable, uniform product.

Oil-in-Water vs. Water-in-Oil

The type of emulsion you’re building determines what kind of emulsifier you’ll need:

In O/W emulsions, the continuous phase is water, so the product tends to feel lighter. In W/O systems, the continuous phase is oil, giving more occlusion and water resistance.

The HLB System (Hydrophilic-Lipophilic Balance)

To choose the right emulsifier, formulators use the HLB system, which rates emulsifiers on a scale of 0 to 20 based on how hydrophilic or lipophilic they are.

• HLB 3–6: Suitable for W/O emulsions

• HLB 8–18: Suitable for O/W emulsions

The oil phase in your formula also has an HLB requirement called the required HLB. Your goal is to match the emulsifier’s HLB (or blend of emulsifiers) to the oil phase’s required HLB for optimal stability.

Some emulsifier systems are pre-optimized and don’t require you to calculate HLB manually, but understanding the principle still helps you troubleshoot and substitute more effectively.

Choosing the Right Emulsifier

Here’s what to consider:

1. System Type

Are you building an oil-in-water or water-in-oil emulsion?

2. Oil Phase Composition

What oils, esters, or silicones are you using? Do they have a high required HLB?

3. Application Needs

Do you want a light feel (e.g., esters, PEG-based emulsifiers) or richness (e.g., polyglyceryl-based, W/O systems)?

4. Processing Constraints

Some emulsifiers require heating; others work cold process. Some need high shear, others don’t.

5. Compatibility and Charge

Is your formula anionic, nonionic, or cationic? Charged emulsifiers don’t always play well with certain actives or polymers.

Common Emulsifiers by System

Oil-in-Water (O/W):

• Polysorbate 60 + Sorbitan Stearate (classic pair)

• Ceteareth-20

• Glyceryl Stearate SE

• PEG-100 Stearate

Water-in-Oil (W/O):

• Sorbitan Oleate

• PEG-30 Dipolyhydroxystearate

• Cetyl PEG/PPG-10/1 Dimethicone

• Polyglyceryl-4 Oleate

Final Thought: Emulsifiers Don’t Work Alone

Even with the right emulsifier, emulsion stability depends on:

• Oil phase composition

• Viscosity modifiers (like cetyl alcohol or carbomer)

• pH control

• Proper mixing and heating

That’s why understanding raw materials, not just using them, is essential to cosmetic formulation.