Emulsions: O/W and W/O Types of emulsion

We all know that oil and water together, are immiscible, it means they do not mix with each other. What if we need a medication, which requires the mixing of both of these ingredients as a disperse system? Have you heard of creams and emulsions or O/W emulsion and W/O emulsion? Let’s understand about this disperse system in little details:

Emulsions are a type of disperse system, where an insoluble liquid phase is dispersed within another liquid phase. Creams are also a type of emulsion, that offer good viscosity and consistency for topical preparations. These preparations are broadly presented in two types.

  • Oil in Water emulsion (o/w): oil as dispersed phase and water as dispersion medium
  • Water in Oil emulsion (w/o): water as the dispersed phase and oil as dispersion medium

O/W emulsion and W/O emulsion


  • Emulsions are difficult to manufacture as two immiscible agents are formulated together to form a dispersed system.
  • These are thermodynamically unstable preparations, hence stabilizers should be used for pharmaceutical preparation.
  • Creams are used for external applications, emulsions may be administered through an IV, rectal or oral route as well.
  •  O/W and W/O preparations are used topically.
  • Emulsions are unstable disperse systems than suspensions, so various excipients are used to stabilize it.
  • O/W preparations: therapeutic agents that have low aqueous solubility are dissolved in the oil phase
  • Some drugs have less palatability due to bitterness. Emulsions help to administer such drugs. A flavoring agent or artificial sweetener is used to mask the taste.
  • Liquid paraffin is administered in o/w emulsion to achieve an optimum cathartic effect. The taste and odor are masked with flavoring agents.
  • Certain drugs may cause irritation if applied topically. These drugs are administered with the help of o/w formulations.
  • emulsions help patient convenience where swallowing solid dosage form is difficult.

O/W emulsion and W/O emulsion: Identification tests

  • Electrical conductivity: Oil in Water emulsion conduct electric current whereas Water in Oil emulsions do not
  • Dilution with water: Oil in Water emulsion may be diluted with water whereas Water in Oil emulsions cannot be diluted.
  • Use of dyes: oil-soluble dyes for o/w emulsion whereas water-soluble dyes for w/o emulsion.

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