Emulsifiers serve an important purpose in cosmetic formulation. Have you ever wondered how your skin cream can contain both water and oils and yet retain a single consistency? If you have ever made a salad dressing you have seen how oil and water do not mix. This is because water is polar, or has a separation of electric charge, while oils and fats (also known as lipids) are non-polar. Emulsifiers form links between these opposites to create a homogenous mixture. Without them, you would have to shake up your products before each use in order to benefit from every ingredient. The active ingredients in many shampoos and other cleansers act as emulsifiers by allowing the oils and dirt in your hair to be washed away by water.
There are multiple types of emulsifiers to suit every formulation need. Oil-in-water emulsifiers typically have a lighter feel due to the larger component of water than oil. On the other hand, water-in-oil emulsifiers have a heavier feel for the opposite reason. There are also water-in-silicone emulsifiers, which can have a heavier feel due to the increased component of silicone. When determining which emulsifier to use in a new formulation, a chemist will pay attention to what is known as the HLB, or hydrophile-lipophile balance. A low HLB means that there are more oil characteristics, and a high HLB means that there are more water characteristics. An emulsifier with a low HLB number is better used in a water-in-oil product (one with more oil than water), while one with a high HLB number is better suited for oil-in-water formulas. An emulsifier with a middle-range number would be used for a mixture of near equal amounts of oils and water.
Unfortunately, emulsifiers have their drawbacks. While it’s beneficial to be able to mix oil and water components when formulating a product, it is not ideal when applied to the skin. Some emulsifiers have been found to dry out skin by increasing TEWL, or transepidermal water loss. This consequently affects the skin’s barrier function, meaning it becomes more permeable to things (whether benign or harmful). Because of this, some emulsifiers can be irritating to the skin. These unfortunate results are thought to be caused by the emulsification effect the product has with the natural oils (lipids) within our skin. Emulsifiers with this effect typically have a high HLB number.
Should you be reducing your exposure to these ingredients? If you have dry and/or sensitive skin, absolutely. A moisturizer containing the wrong emulsifier could in fact be drying out your skin rather than hydrating it. However, not every type of emulsifier has been found to have this effect. Some emulsifiers can actually benefit the skin indirectly by helping other ingredients “stick” to it more. Additionally, the use of emulsifiers with a lower HLB ratio and in lower concentrations  may be gentler on the skin. As this becomes a more prominent issue for consumers, formulators will likely turn to those emulsifiers more often.