You might think of surfactants as just an ingredient in detergents that makes sudsy bubbles, but that’s not the primary function of a surfactant. In fact, the human body produces its own surfactants and I am pretty sure there aren’t any self-sudsing humans out there! All joking aside, surfactants serve a very specific purpose, simply put they reduce the surface tension of water. This essentially makes the molecules “slippery” and breaks down the interface between water and oils. In fact, the word “surfactant” comes from the term surface active agent and the different surfactants are classified based on the nature of the hydrophilic (water-loving) “head groups”. Surfactants can act as foaming agents, but also as wetting agents, emulsifiers, and dispersants. This is important to know in order to understand the different types of surfactants and the purpose they serve in hair and skincare products.
These surfactants are typically water soluble and have a negatively charged hydrophilic group–they are what we commonly think of as the sudsing, bubbly ingredient in shampoos and washes. This surfactant group ionizes when added to water and forms a negative charge. The negative charge allows them to bind to positively charged particles like clay and soils. When reading the ingredients in your products, you can identify anionic surfactants as those that have the following in their names:
Cationic surfactants have a positively charged hydrophilic group and are not typically used for cleaning. These tend to rapidly absorb and “stick” to surfaces and are harder to rinse off. This makes them great for using as conditioning agents for hair and skincare formulations.
These surfactants are great for solubilizing oils and fragrances and generally have low foam. They are also considered to be more gentle and therefore are used in formulating gentle cleansing solutions like baby washes and kids shampoo. Nonionic surfactants include:
These surfactants form both negative and positive charges depending on the pH of the formulation. These surfactants can increase foaming and reduce irritation so they are also used as a secondary surfactant. A classic example of an amphoteric surfactant is Cocamidopropyl Betaine.
Surfactants are very versatile and not just for making bubbles. Depending on what the formulator is looking for, a surfactant system can be balanced for any formulation to produce suds, to help solubilize oils, and for conditioning.