Every moisturiser, lotion, and cream is an emulsion — a mixture of oil and water that has been forced into a stable, homogeneous state by the addition of an emulsifier. Without the emulsifier, the oil and water phases would separate within minutes. The emulsifier's job is to sit at the interface between the two phases and prevent that separation.
Oil-in-Water vs Water-in-Oil
The two primary emulsion types are oil-in-water (O/W) and water-in-oil (W/O). In an O/W emulsion, oil droplets are dispersed throughout a continuous water phase. In a W/O emulsion, water droplets are dispersed throughout a continuous oil phase.
"The emulsion type determines the product's texture, absorption rate, and occlusive properties more than any individual ingredient."
O/W emulsions feel lighter, absorb faster, and are less occlusive. Most serums, lightweight moisturisers, and day creams are O/W. W/O emulsions feel richer, are more occlusive, and are better suited to dry or compromised skin. Many night creams and barrier repair products are W/O.
The HLB System
The Hydrophilic-Lipophilic Balance (HLB) system assigns a numerical value to emulsifiers based on their relative affinity for water versus oil. Emulsifiers with HLB values of 8–18 are suitable for O/W emulsions. Those with HLB values of 3–6 are suitable for W/O emulsions.
Common O/W emulsifiers you will see on INCI lists include Cetearyl Alcohol combined with Ceteareth-20, Glyceryl Stearate combined with PEG-100 Stearate, and various polysorbates. The presence of two emulsifiers — one with a higher HLB and one with a lower HLB — in a formula is a sign of careful formulation: the combination creates a more stable emulsion than either alone.
What This Means for Label Reading
The emulsifier system in a formula tells you a great deal about the intended texture and performance. A formula with Cetearyl Alcohol and Ceteareth-20 as the primary emulsifiers will have a different skin feel than one using Glyceryl Stearate SE or a natural wax-based system. Learning to recognise the common emulsifier combinations is one of the most useful skills in INCI literacy.
Oil-in-Water vs. Water-in-Oil Emulsions
The two primary emulsion types have fundamentally different properties and applications:
Oil-in-water (O/W) emulsions: Water is the continuous phase; oil droplets are dispersed within it. These feel lighter, absorb more quickly, and are easier to spread. Most serums, lotions, and lightweight moisturisers are O/W emulsions. They are less occlusive than W/O emulsions and better suited to normal-to-oily skin types.
Water-in-oil (W/O) emulsions: Oil is the continuous phase; water droplets are dispersed within it. These feel richer, provide greater occlusion, and are more resistant to water. Cold creams, barrier creams, and some sunscreens are W/O emulsions. They are better suited to very dry or compromised skin types.
The emulsion type can often be inferred from the INCI list: if water (Aqua) is the first ingredient, it is almost certainly an O/W emulsion. If an oil or wax appears first, it may be a W/O emulsion.
Common Emulsifier Systems and What They Tell You
Cetearyl Alcohol + Ceteareth-20: One of the most common emulsifier combinations in conventional cosmetics. Cetearyl alcohol is a fatty alcohol that provides structure and emolliency; Ceteareth-20 is the emulsifying agent. This combination produces stable, creamy emulsions with a classic moisturiser texture. Well-tolerated by most skin types.
Glyceryl Stearate + PEG-100 Stearate: Another common conventional emulsifier pair. Produces lighter, more fluid emulsions than the cetearyl alcohol system. Often used in serums and lightweight moisturisers.
Glyceryl Stearate SE: A self-emulsifying form of glyceryl stearate that can form emulsions without a co-emulsifier. Used in simpler formulations and "clean" beauty products. Produces stable emulsions but may have a slightly less elegant skin feel than multi-component systems.
Lecithin (Phosphatidylcholine): A natural emulsifier derived from soy, sunflower, or egg. Produces liposomal structures that can enhance active ingredient delivery. Used in premium and "natural" formulations. More expensive and less stable than synthetic emulsifiers.
Polyglyceryl Esters (Polyglyceryl-3 Methylglucose Distearate, Polyglyceryl-6 Distearate): A family of mild, skin-compatible emulsifiers increasingly used in "clean" and sensitive-skin formulations. Generally well-tolerated and biodegradable.
The Role of Co-Emulsifiers and Stabilisers
Most emulsions use a primary emulsifier in combination with co-emulsifiers and stabilisers:
Fatty alcohols (Cetyl Alcohol, Stearyl Alcohol, Cetearyl Alcohol): Provide structure, increase viscosity, and act as co-emulsifiers. Their presence in an INCI list is a positive stability signal.
Carbomer, Xanthan Gum, Hydroxyethylcellulose: Rheology modifiers that increase viscosity and improve emulsion stability. Their presence does not indicate emulsion type but suggests the formulator has addressed stability.
Magnesium Aluminum Silicate, Silica: Inorganic stabilisers that improve emulsion stability, particularly in W/O systems.
Emulsifier-Free Formulations
A growing category of "emulsifier-free" moisturisers uses alternative approaches to combine oil and water phases:
Lamellar gels: Use fatty alcohols and surfactants to create a lamellar (layered) structure that mimics the skin's own lipid organisation. Brands like Dermalogica and some pharmaceutical brands use this approach.
Microemulsions: Thermodynamically stable systems that form spontaneously without mechanical emulsification. Require specific ratios of oil, water, and surfactant.
Anhydrous formulations: Avoid the oil-water combination entirely. Balms, facial oils, and some serums are anhydrous — they contain no water and therefore require no emulsifier and no preservative.
What Emulsifiers Tell You About a Formula
The emulsifier system is one of the most informative sections of an INCI list for understanding a product's intended performance:
- Multiple emulsifiers suggest a complex, carefully engineered formula - A single self-emulsifying ingredient suggests a simpler formulation - The presence of lecithin or polyglyceryl esters suggests a "clean" or sensitive-skin positioning - The absence of any recognisable emulsifier in a product claiming to be a cream or lotion is a red flag — either the product is anhydrous, or the emulsifier is listed under an unfamiliar name
The Bottom Line
Emulsification is the invisible architecture of every moisturiser, serum, and cream. Understanding the emulsifier system in a formula gives you insight into its texture, stability, skin feel, and formulation philosophy that no marketing claim can provide.
The emulsifier system in a formula tells you a great deal about the intended texture and performance. Learning to recognise the common emulsifier combinations is one of the most useful skills in INCI literacy.
