In an oil-in-water emulsion, water is the continuous phase and oil exists as dispersed droplets. In a water-in-oil emulsion, the opposite is true.

Phase inversion occurs when formulation or processing conditions cause the preferred continuous phase to change.

Causes

Potential causes include changes in phase ratio, temperature, emulsifier characteristics, electrolyte concentration and mechanical processing.

Some emulsifier systems are deliberately processed close to a phase-inversion region to create very fine droplets.

Uncontrolled Inversion

Uncontrolled phase inversion is generally considered a formulation failure because it can cause dramatic changes in viscosity, appearance, conductivity, texture and stability.

It can occur during manufacturing or during storage.

References

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

‍