Emulsions

Disperse preparations, more or less viscous, for external or internal use, consisting of two or more liquids which are not soluble in each other. One of the phases is usually water, the second ("oil phase") is an organic liquid immiscible with water, often a hydrocarbon or in fact a real oil.

Emulsions usually contain emulsifiers corresponding to the emulsion type to increase stability, often also viscosity increasing additives, e.g. organic hydrogel formers in the outer phase.

In dermatology the hydrophilic skin emulsion base is used for the production of emulsions according to extemporaneous preparations (see below base emulsion hydrophilic (NRF p.25.).

S.a. Microemulsions

Simple emulsion systems (two immiscible liquids):

• O/W emulsion (oil as inner, open or disperse phase, water as outer or closed phase = dispersing agent), they are susceptible to microorganisms (bacteria, moulds) and must therefore be preserved (p-hydroxybenzoic acid ester, sorbic acid, potassium sorbate).
• W/O emulsion (water as inner, open or disperse phase, oil as outer or closed phase = dispersion agent).
• Both phases can vary their viscosity from liquid to semi-solid. Thus, the range of preparations also extends from the low-viscosity lotio to the semisolid cream.
• Besides the O/W and W/O emulsions there is also the mixed type of the ambiphilic system in which both phases are diffusely distributed next to each other and at least in partial Bezirekn (bicoherent phase distribution) (Loebich F 1985).