To prepare a cosmetic product, you have to combine an oil phase with an aqua phase. To do this you have to use an emulsion. Emulsions are substances that can mix two or more components (e.g., an oily and an aqueous). They are distinguished in oil in water and water in oil emulsions, according to their hydrophilic or hydrophobic groups. There are lot of emulsions. Each one gives a different texture to final product, and changesproduct’s viscosity according to your will.