Why do cosmetics need surfactants?

Common cosmetics are generally in paste or cream form, which contain both oil and water, and are very evenly dispersed. Water and oil are incompatible, 

so how can they coexist peacefully in skin care products? This is where surfactants play an important role - Emulsification. In the water-based environment, 

the surfactant forms micelles, wrapping the small particles of oil in the center of the micelle, which is equivalent to putting a hydrophilic coat on the outside of the oil particles, 

so that they can be freely and evenly dispersed in the water, forming a stable emulsion. When the lotion is applied to the skin, these micelles break, releasing oil particles (often the active ingredient in cosmetics) that are absorbed by the skin.

Not all cosmetic active ingredients are oil-based, and some active ingredients are water-soluble, so oil and water components need to be evenly distributed. 

In addition, the active ingredients of pure oil are very unattractive in pure products or high concentrations, and probably no one will want to put them on the face or body; 

High concentrations of active ingredients are also not optimal for skin care - glycerin, for example, moisturizes, but must be diluted with water, and pure glycerin, 

instead of moisturizing, wicks moisture away from the skin. Therefore, the production of emulsion is not only more beautiful, but also properly diluted the active ingredients, 

so that they can play a better effect. So, can we buy high concentrations of skincare active ingredients and dilute them ourselves when we use them? This idea is not practical, because it is not only inconvenient, but also difficult to control the ratio of water to oil. Let the professionals who make cosmetics do it for us.

In the case discussed above, surfactants play a behind-the-scenes role in cosmetics, but for cleaning cosmetics, such as face washes and shampoos, 

surfactants play a leading role. One of the properties of surfactants is their ability to remove oil. Of course, the skin can not stand soap, laundry detergent as strong surfactants, 

so general cosmetics will choose mild non-irritating, and not easy to cause allergic reactions of surfactants.

In addition, surfactants can also play a condition role. Because they generally have "oily" parts (oleophilic groups), surfactants can improve the feel of the skin or hair, 

and can play a certain care role in themselves. For example, Stearalkonium Chloride, commonly used in hair conditioners, is a cationic surfactant, whose hydrophilic groups are positively charged, so that they can be attracted by the negative charge of the damaged protein parts of the hair, which is not easy to be washed away, 

and can stay on the hair to play a role in care. Because the damaged negatively charged hair repds each other, the use of cationic surfactant quaternary ammonium salt, 

such as behentrimonium chloride, can also neutralize the electrical properties and reduce the effect of fridness.

It can be seen that surfactants play a variety of roles in cosmetics such as emulsification, cleaning and care, and cosmetics can not be separated from them. 

In recent decades, liposome, a new surfactant used in cosmetics, has made the care effect of cosmetics more effective.