Emulsifiers are indispensable ingredients for preparing many cosmetics, including body and face creams.
Let's see what the natural emulsifiers are and how they are chosen.
What are emulsifiers and what are they used for
Many cosmetics we buy are emulsions, from face cream to cleansing milk, from body cream to sun protection.
Chemically, the emulsions consist of a system in which a liquid is distributed evenly in another liquid, in the form of small droplets: the system is therefore composed of a dispersed phase and a dispersing phase.
If the dispersed phase consists of an oil or a mixture of oils and the dispersing phase is aqueous, it is called "oil in water" emulsions, often indicated with O / A; on the contrary, water-in-oil (or A / O) emulsions are defined as the systems in which the dispersed phase is represented by water and the dispersing phase consists of an oil or a mixture of oils.
Since water and oil are not miscible with each other, the emulsions are stabilized thanks to the use of emulsifying agents, surface- active substances that reduce the surface tension of the phase in which they are less soluble, favoring their fragmentation into drops.
The emulsifiers are therefore substances endowed with a certain degree of solubility both in water and in oil: each emulsifier has its own hydrophilic-lipophilic balance value (or HLB, hydrophilic-lipophilic balance), given by the ratio between the hydrophilic and lipophilic component of the molecule.
In general, the emulsifiers which have an HLB of between 4 and 6 are suitable for obtaining water-in-oil emulsions, those having an HLB of between 8 and 18 give oil-in-water emulsions instead.
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Natural emulsifiers: what they are
Emulsifiers, as we have seen, are substances capable of keeping together aqueous and oily phases, which cannot normally be mixed together. A natural emulsifier is lecithin: soy lecithin is in fact used in the food industry as an emulsifier. In DIY cosmetics, soy lecithin is used to prepare cold emulsions.
Other emulsifiers used in cosmetics are produced by the sterilization of a fatty acid and a sugar : Sucrose stearate and Methyl glucose sesquistearate are part of this category.
Further examples of emulsifiers are the esters of fatty acids and glycerol, such as Glyceryl stearate and the alcohols of fatty acids, including cetyl alcohol ( Cetyl alcohol ).
Unlike soy lecithin, which is also readily available at the supermarket, to buy these emulsifiers you have to turn to shops that specialize in selling cosmetic raw materials.
Natural emulsifiers: how to choose them
When an emulsion is formulated, the choice depends on both the HLB of the emulsifier and the HLB required by the oil or mixture of cosmetic oils that is being formulated.
The required HLB depends on the type of emulsion to be obtained: in general, vegetable oils and butters have a required HLB of 4.5-5.5 to formulate water-in-oil emulsions and a required HLB of 10-11 for the oil-in-water emulsions. The waxes have instead HLB between 5 and 8 for water in oil emulsions and between 10 and 16 for oil in water emulsions.
Once we have established the type of emulsion we wish to achieve and the required HLB value, we identify the emulsifier to be used: in any case, experts advise mixing two emulsifiers, one with a high HLB and one with a low HLB, since it was noted empirically that the emulsions obtained with this method are more stable .
