ABSTRACT
Hair looks much better when it is washed regularly and, until recently, this was done using soap. In much of the world, shampoos have now taken over, and they are much more complicated compositions. Apart from the surfactant detergent, they contain a chelating agent like Na4EDTA to remove Ca2+ and Mg2+ (which would otherwise remove some surfactants), a pH adjuster (e.g., sodium citrate) to keep the pH slightly on the acid side of neutral to give a smooth cuticle, foam stabilisers, bactericides, and preservatives-not to mention fragrances, dyes, and other additives to improve the look for marketing purposes. It is the detergents that are the most important; they must contain a hydrophilic head and at least one hydrophobic tail. These can be anionic, cationic, or zwitterionic. Anionic detergents tend to be the main foaming and cleansing component; the most widely used types are exempli†ed by sodium lauryl sulfate (sodium dodecyl sulfate; 7.1), sodium stearate (sodium octadecanoate; 7.2), sodium dodecylbenzenesulfonate (7.3). Cocamidopropyl betaine (CAPB; 7.4) is an important zwitterionic surfactant, with a mild detergent action that is also more viscous than the other types of surfactant.
