If you have ever made a lotion that looked perfect when you first made it and then separated into an oily puddle within 24 hours, you already know the most important lesson in emulsion chemistry: stability is not accidental. It is the result of selecting the right emulsifier for your specific oil phase, processing at the correct temperature, and understanding the physical chemistry that holds oil and water together.
Emulsifiers are the most technically demanding ingredient category in cosmetic formulation. Unlike surfactants, which are selected primarily on mildness and foaming profile, emulsifiers must be matched to the polarity of your oil phase, the intended emulsion type, the processing method, and the electrolyte load of your formula. Getting this wrong produces formulas that separate, soap, or fail stability testing within weeks.
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Oil-in-Water vs Water-in-Oil: Choosing the Right Emulsion Type
An emulsion is a mixture of two immiscible liquids, one dispersed as droplets within the other. In cosmetic formulation, the two most common emulsion types are oil-in-water (O/W) and water-in-oil (W/O). Understanding the difference is the first step in selecting the correct emulsifier.
In an oil-in-water emulsion, oil droplets are dispersed within a continuous water phase. This is the most common emulsion type in cosmetic formulation. O/W emulsions are lighter in texture, absorb more readily into the skin, and are easier to manufacture than W/O emulsions. Most lotions, serums, and lightweight creams are O/W emulsions. They require emulsifiers with a relatively high HLB value (8–18).
In a water-in-oil emulsion, water droplets are dispersed within a continuous oil phase. W/O emulsions are richer, more occlusive, and provide a stronger barrier function. They are used in heavy creams, barrier balms, and sunscreen formulations. They require emulsifiers with a low HLB value (3–6) and are significantly more difficult to manufacture than O/W emulsions.
Key Emulsifier Profiles for Australian Formulators
| Emulsifier | INCI Name | Type | Usage Rate | Key Characteristics |
|---|---|---|---|---|
| Olivem 1000 | Cetearyl Olivate, Sorbitan Olivate | O/W | 3–8% | Forms liquid crystalline structures; excellent skin feel; COSMOS-approved |
| Montanov 68 | Cetearyl Alcohol, Cetearyl Glucoside | O/W | 2–6% | Stable across wide pH range; good electrolyte tolerance; natural origin |
| Natragem EW | Glyceryl Stearate, PEG-100 Stearate | O/W | 2–5% | Easy to use; broad compatibility; suitable for beginners |
| Arlacel 1689 | Polyglyceryl-3 Methylglucose Distearate | O/W | 2–5% | Polymeric; excellent stability; suitable for high-electrolyte formulas |
| Arlacel 1690 | Sucrose Polystearate | O/W | 1–4% | Polymeric; very stable; COSMOS-approved; suitable for sensitive skin |
The Liquid Crystalline Network: Why Olivem 1000 Behaves Differently
Most emulsifiers work by reducing the interfacial tension between oil and water, allowing them to mix. Olivem 1000 works differently. When combined with water and oil at the correct temperature and concentration, it forms a liquid crystalline lamellar network, a structured arrangement of alternating oil and water layers that mimics the architecture of the skin's own lipid barrier.
This liquid crystalline structure provides several advantages over conventional emulsions. It is inherently more stable because the lamellar structure physically prevents oil droplets from coalescing. It delivers active ingredients more effectively because the lamellar structure is compatible with the skin's own barrier. And it produces a distinctive skin feel, a light, non-greasy texture that absorbs rapidly, that is difficult to replicate with conventional emulsifiers.
The trade-off is that Olivem 1000 is sensitive to processing temperature. The emulsion must be formed above the melting point of the liquid crystalline phase (approximately 70–75°C) and then cooled slowly and with gentle agitation. Rapid cooling or excessive shear disrupts the lamellar structure and produces an unstable emulsion.
The 24-Hour Evaluation Rule
One of the most common mistakes in emulsion formulation is evaluating stability too early. A freshly made emulsion will almost always look stable immediately after manufacture. The real test is what happens over the following 24–72 hours as the emulsion equilibrates to room temperature and the emulsifier network fully sets.
The professional standard is to evaluate emulsions at 24 hours, 48 hours, and 7 days at room temperature, and to run parallel samples at 40°C and at 4°C to assess temperature stability. An emulsion that passes all three temperature conditions at 7 days is likely to be stable for at least 3 months under normal storage conditions. An emulsion that separates at 40°C within 24 hours will not survive an Australian summer on a retail shelf.
A Professional O/W Lotion Formula
| Phase | Ingredient | INCI Name | % (w/w) | Grams (100g batch) |
|---|---|---|---|---|
| A (water) | Distilled Water | Aqua | 72.5% | 72.5g |
| A (water) | Glycerin | Glycerin | 3.0% | 3.0g |
| B (oil) | Jojoba Oil | Simmondsia Chinensis Seed Oil | 8.0% | 8.0g |
| B (oil) | Shea Butter | Butyrospermum Parkii Butter | 4.0% | 4.0g |
| B (oil) | Cetyl Alcohol | Cetyl Alcohol | 1.5% | 1.5g |
| B (oil) | Olivem 1000 | Cetearyl Olivate, Sorbitan Olivate | 5.0% | 5.0g |
| C (cool down) | Niacinamide | Niacinamide | 3.0% | 3.0g |
| C (cool down) | Allantoin | Allantoin | 0.5% | 0.5g |
| C (cool down) | Preservative | Per supplier spec | 1.0% | 1.0g |
| C (cool down) | Citric Acid (50% solution) | Citric Acid | q.s. | q.s. to pH 5.5 |
| Total | 100% | 100g |
Method: Heat Phase A and Phase B separately to 75°C. Add Phase B to Phase A with constant stirring. Homogenise for 2–3 minutes. Cool to 40°C with gentle agitation. Add Phase C ingredients one at a time, mixing well after each addition. Adjust pH to 5.0–5.5 with citric acid solution. Package immediately.
Troubleshooting Common Emulsion Failures
| Problem | Cause | Solution |
|---|---|---|
| Emulsion separates within 24 hours | Insufficient emulsifier or wrong emulsifier type for oil phase | Increase emulsifier to upper end of usage range; verify HLB compatibility with oil phase |
| Soaping effect (white, soapy feel on skin) | Emulsifier reacting with hard water or high-pH formula | Add chelating agent (EDTA 0.1%); reduce pH to 5.5–6.0 |
| Low viscosity / watery texture | Insufficient fatty alcohol or thickener | Increase cetyl or cetearyl alcohol by 1–2%; add Carbomer or HEC at 0.3–0.5% |
| Grainy texture after cooling | Rapid cooling causing crystallisation of fatty alcohols or butters | Cool slowly with gentle agitation; avoid refrigerating during manufacture |
Frequently Asked Questions
An emulsifier is the primary ingredient responsible for creating and stabilising the emulsion. A co-emulsifier is a secondary ingredient that supports the primary emulsifier by increasing the stability of the interfacial film between oil and water. Fatty alcohols such as cetyl alcohol and cetearyl alcohol are the most commonly used co-emulsifiers in O/W lotion formulation. They also contribute to viscosity and skin feel.
Yes. Combining two compatible emulsifiers can improve stability and skin feel. Olivem 1000 and Montanov 68 are both O/W emulsifiers with similar HLB values and are compatible in the same formula. A typical combination would be 3–4% Olivem 1000 and 2–3% Montanov 68, with the total emulsifier level adjusted based on the oil phase percentage.
As a general rule, the emulsifier percentage should be approximately 25–30% of the total oil phase percentage. For a formula with a 15% oil phase, you would typically use 3.75–4.5% emulsifier. This is a starting point, not a fixed rule. The optimal emulsifier level for your specific formula should be determined through stability testing.
Many active ingredients, particularly those that are highly electrolytic (such as Niacinamide at high concentrations, Vitamin C, and AHAs), can destabilise emulsions by disrupting the emulsifier network. Polymeric emulsifiers such as Arlacel 1689 and Arlacel 1690 are significantly more tolerant of electrolytes than conventional emulsifiers. If you are formulating with high concentrations of electrolytic actives, switch to a polymeric emulsifier system.
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Get the Emulsifier GuideDisclaimer: All ingredients and products referenced in this article are intended for cosmetic use only. No therapeutic, medicinal, or TGA-regulated claims are made or implied. Always conduct a patch test before use and ensure your finished formulations comply with Australian cosmetic regulations.