This is the process when an O/W emulsion changes to a W/O emulsion or vice versa.

As already mentioned, soaps of monovalent metals produce O/W emulsions, whereas soaps of divalent metals produce W/O emulsions. The emulsion type is determined by the solubility of the emulsifying agent. If it is more soluble in water than in oil, the water will be the continuous phase and vice versa. The addition of a substance that alters the solubility of the emulsifying agent may cause reversal of the phases. For example, if calcium chloride is added to an O/W emulsion stabilized by sodium soap, phase reversal may occur resulting in a W/O emulsion.

For stability of an emulsion, the optimum range of concentration of the dispersed phase is 30%–60% of the total volume. If the concentration of disperse phase exceeds this concentration, phase inversion occurs.

Phase inversion can be minimized by using the proper emulsifying agent in adequate concentration, keeping the concentration of dispersed phase between 30% and 60% and storing the emulsion in a cool place.