75 Chapter 3 Shampoo and Conditioner Science Robert Y. Lochhead University of Southern Mississippi Shampoos and conditioners are the highest volume products in personal care, in terms of products sold. In this chapter, we will consider the science that underpins the functioning of these product types. The principal function of shampoos is still to cleanse the hair. However, since the introduction of two-in-one shampoos in the 1970s it has not been sufficient for a shampoo to merely cleanse the hair. Modern shampoos should at least cleanse, condition, make the hair easier to style, and fragrance the hair with a pleasant smell that lingers. Modern conditioners should lower the friction between hair fibers to allow easier grooming and alignment of the hair fibers while leaving them glossy and avoiding lankness. The science of shampoos and conditioners is still evolving and in addition to describing fundamentals, this chapter attempts to take the reader to the frontiers of research in shampoo and conditioner science. Introduction Located within the hair follicle is a sebaceous gland that continuously excretes an oily material, known as sebum, onto the hair and scalp. This substance consists of compounds such as fatty acids, hydrocarbons and triglycerides, and serves as nature’s conditioning treatment—providing lubrication and surface