Advances in Hair Styling 434 Hair styling products primarily use liquefied gases. These gas types not only provide for relatively consistent delivery, they aid in sprayability and in mousses provide foam aesthetics. Compressed gases do not offer these benefits in traditional aerosol hair care products but may find application in alternative aerosol packages such as bag-on-valve (BOV) technology. The guiding principle in the development of an aerosol system is that there is a sensitive balance between performance, aesthetics, and the physicochemical properties of the system, as well as the additional constraint of regulatory requirements. The complete aerosol package is a complex system involving not only multiple components and variables but their interaction as well. Keeping this formulation principle in mind along with a firm knowledge of ingredients employed in aerosol systems and options in componentry, the formulation chemist will find success in matching desired project profiles. Hair styling/conditioning mousses: The aerosol mousse has been around since the early 1980s. At first it was projected that the product form would just be a fad soon to die out. Then in October of 1988, Consumer Reports did a formal study of 39 brands of mousse that showed conclusively how much this product segment had evolved over just a few years.27 Aerosol mousses, especially those of the major brands, still occupy store shelves today. Formulating mousses has changed over the years due primarily to the change in the amount of propellant and/or alcohol that can be used following the creation of VOC regulations in the 1990s. It was not unusual for mousses to contain 15% alcohol which allowed the product to produce nice foam but break quickly during application. Now that formulas are alcohol-free this desirable quality is harder to achieve. There are several essential ingredients of a mousse formulation. A small amount of surfactant, preferably nonionic, produces the foam during actuation. The fixative polymer provides conditioning and styling, as well as giving the foam a particular aesthetic feel.