Chapter 3 91 During the 1970s, triethanolamine lauryl sulfate was preferred as a primary surfactant due to its excellent cleaning properties and luxurious flash foaming capability. However, it was replaced by laureth sulfates for two reasons, namely, the concern over the formation of nitrosamines from secondary amine components and the reduced eye irritation exhibited by the laureth sulfates. Over the last two decades the primary surfactants of most shampoos have been sodium laureth sulfate, ammonium lauryl sulfate, and sodium lauryl sulfate. The Co-surfactant: The co-surfactant–often called the foam booster–has most prominently been selected from two types of materials: alkylamide MEA and alkylamidobetaines. Modern shampoos contain primarily betaines as co-surfactants. Enhancing Mildness Isethionates are surfactants that have been noted for their mildness to skin and for at least three decades they have been the basis of non-soap detergent bars such as Dove (Unilever). They have been making inroads into shampoos based upon mildness claims. Moreover, Unilever researchers have discovered that the mildness can be enhanced even further by including mildness benefit agents that can be flocculated by cationic polymers present in the formulation and delivered as flocs upon dilution of the formulation.36 The preferred benefit agent in this case is petrolatum and the cationic polymers are well known polymers like polyquaternium-10 and guar hydroxypropyltrimonium chloride. This could form the basis of shampoos that are mild to the skin. Certain non-cross-linked linear acrylic copolymers can lower the irritation potential of surfactants and provide products that are both clear and highly foaming.37 The preferred polymers interact with the surfactant and effectively shift the CMC to higher concentrations, while lowering the critical aggregation concentration, the latter being the concentration at which the surfactant selectively interacts with the polymer rather than adsorbing at the liquid surface (Figure 15). It is postulated that free surfactant molecules and free