Water-in-Oil Emulsions (W/O) – Cosmetic Uses in Emollient Skin Care

What Are Water-in-Oil Emulsions?

Water-in-oil (W/O) emulsions consist of water droplets dispersed throughout a continuous oil phase. Although less common than oil-in-water emulsions, they can be desirable when a more emollient skin feel or enhanced release of certain ingredients is required.

W/O emulsions typically contain approximately 45–80% oil phase, resulting in formulations that can provide a richer and more protective sensory profile.

Emulsifier Selection

Emulsifiers with an HLB range of approximately 2.5–6 are frequently selected for W/O systems. When several emulsifiers are used, the predominant emulsifier is generally lipophilic, with a smaller amount of a hydrophilic emulsifier.

Sorbitan stearates and sorbitan oleates can be effective emulsifiers for W/O systems. Sorbitan isostearates, which have branched hydrocarbon chains, can also contribute to a more uniform particle size distribution.

Anionic emulsifiers are generally less efficient as W/O emulsion stabilisers because larger amounts of surface-active material may be required.

Emollients and Sensory Properties

Modern W/O formulations can be developed with a more elegant skin feel by selecting suitable esters, Guerbet alcohols, silicones, and other emollients.

The choice of emollient depends on several factors, including:

• Spreading behaviour on the skin
• Tackiness
• Dermal compatibility
• Polarity
• Molecular weight
• Perceived sensory elegance

Research has shown relationships between the molecular weight of emollients and the viscosity of W/O creams. Higher-molecular-weight co-emulsifiers combined with higher-molecular-weight emollients have also been associated with improved emulsion stability.

Emollients or combinations of emollients with medium polarity have demonstrated favourable stability characteristics in W/O lotion systems.

Cosmetic Applications

W/O emulsions are particularly useful for cosmetic products where a rich, emollient texture is desired. Their continuous oil phase can contribute to a distinctive application and afterfeel compared with conventional O/W emulsions.

They can therefore be considered for richer creams, protective skin-care products, and other formulations where emolliency and sensory performance are important.

Source: Handbook of Cosmetic Science and Technology - André O. Barel, Marc Paye, Howard I. Maibach