The formulation of emulsions involves the following:

1. Oil phase: The oil (medicament or vehicle) used for the preparation of emulsion may be of fixed oil, mineral oil, volatile oil or oleo resin type. Depending upon the origin, suitable ratio of oil, water and emulgent must be used for the preparation of primary emulsion.
2. Aqueous phase: Freshly boiled and cooled purified water is normally used because of the increased risk of microbial contamination.
3. Preservative: The desirable features of a preservative suitable for use in an emulsion include the following:
   • Wide spectrum of activity against all bacteria, yeast and molds
   • Bactericidal rather than bacteriostatic activity
   •  Freedom from toxic, irritant and sensitizing activity
   •  High-water solubility. Because the growth of microorganisms occurs in the aqueous phase, it is important that the preservative has a low O/W partition coefficient. The more polar the oil phase, the more difficult it is to preserve the product adequately, owing to the solubility of the preservative in both the phases.
   • Compatibility with the other ingredients in the preparation and with the container
   •  Stability and effectiveness over a wide range of pH and temperature
   •  Freedom from color and odor
   •  Retention of activity in the presence of large number of microorganismsExamples are benzoic acid (0.1%–0.2%), methyl and propyl paraben (0.1%–0.2%), chloroform (0.25%), chlorocresol (0.1%) and phenyl mercuric nitrate (0.004%–0.01%).
4. Emulsifying agent (emulgent): The quantity of emulsifying agent added is determined by the type of oil to be emulsified and the quantity of emulsion to be prepared.
5. Antioxidant: This is used to increase the stability of the oil phase in the emulsion by preventing the oxidation of the oil during its shelf life. Examples are butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT) and tocopherol.
6. Flavoring agent: This is used to increase the palatability of the final preparation. Examples are pineapple, orange, chocolate and mint flavors.
7. Coloring agent: This is used to identify the preparation and to increase the aesthetic appeal of the preparation. Examples are Food, Drug and Cosmetic Act-approved colors such as erythrosine and tartrazine.
8. Perfume: This is used only for external preparations such as creams