Co-emulsifiers support the primary emulsifier in forming and stabilizing an emulsion. They can contribute to the structure of the interfacial layer surrounding droplets and can also increase the viscosity of the continuous phase.

Common cosmetic co-emulsifiers include fatty alcohols such as cetyl alcohol, stearyl alcohol and cetearyl alcohol.

These materials can provide several functions simultaneously. They may improve emulsion stability, increase creaminess, modify spreadability and create a more substantive skin feel.

Formulation Considerations

The effect of a co-emulsifier depends strongly on the primary emulsifier and the oil phase. A fatty alcohol that performs well in one emulsifier system may produce a very different texture in another.

Concentration is also important. Excessive levels can create a waxy or heavy skin feel and may alter the melting characteristics of the product.

Processing

Many co-emulsifiers require heating to melt completely and should be incorporated into the appropriate phase before emulsification.

Cooling conditions can influence the final crystalline and lamellar structure of the formulation.

References

Barel, A. O., Paye, M. and Maibach, H. I. Handbook of Cosmetic Science and Technology. CRC Press.

Lachman, L., Lieberman, H. A. and Kanig, J. L. The Theory and Practice of Industrial Pharmacy.

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