(a) Water-in-oil (w/o) emulsion (Dispersed phase – water, Continuous phase – oil)

(b) Oil-in water (o/w) emulsion (Dispersed phase – oil, Continuous phase – water)

(c) Multiple emulsion (Water-in-oil-in-water (w/o/w), Oil-in water-in oil (o/w/o))

(d) Miscellaneous : Globule size or the disperse phase size of emulsion can vary enormously but are commonly in the range of 0.25-25pm diameter.

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On the basis of size emulsions are mainly of three types

(i) Coarse emulsion: globule size more than 25.0 pm.

(ii) Fine emulsion: globule size less than 5.0 pm.

(iii) Microemulsion or miceller emulsion: globule size range of 10-75 nm, such emulsions appear transparent to the human eye in day light.

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Oil-in-water (o/w) Emulsion

In this emulsion oil is the dispersed phase (internal phase) and aqueous is the dispersion medium (external phase). These emulsions are used mainly for internal/oral use to mask the bitter or disagreeable taste and odor of drugs. External preparations of these emulsions are used for formulating non-greasy lotions, creams and liniments. Moreover easy assimilation of oil in the body takes place as oil is present in a finely dispersed state. Cosmetic products prepared using o/w emulsions can easily be removed from the surface of the skin e.g., castor oil emulsion, foundation creams, vanishing creams.

Water in oil (w/o) emulsions

In this emulsion water is the dispersed phase (internal phase) and oil is the dispersion medium (external phase). These emulsions are mainly used for external preparations e.g., lotions and creams as the external layer of oil forms an occlusive film and prevents the evaporation of moisture from the surface of the skin. They are also effective as cleansing cream as they solubilize the oil soluble dirt from the surface e.g. Cold creams.

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Multiple Emulsions

In this emulsion, oil in water {o/w) or water in oil emulsion (w/o) is dispersed in another liquid medium. Thus, oil-in-water-in-oil (o/w/o) emulsion consists of very small droplets of oil dispersed in the water globules of water in oil emulsion and water-in-oil-in-water (w/o/w) emulsion consists of droplets of water dispersed in the oily phase of oil in water emulsion. Multiple emulsions are primarily used for formulating sustained release dosage forms as the drug entrapped in the innermost layer has to pass through the other two phases before being released for absorption.