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This is an abridged version of an article published in the December 2011 issue of Cosmetics & Toiletries magazine.
The primary purpose of a shampoo is to clean the hair and scalp; all other attributes such as styling, conditioning split ends, adding shine and improving combability are accomplished by grooming tasks and used for claim purposes to differentiate a product from the competition. Shampoos are different from other cleansing products in that they must function at relatively low, mild temperature conditions; provide instant foam; and leave no residue after rinsing. With regard to their delivery to hair, shampoos must have a viscosity and rheology that allows them to stay on the palm of a consumer’s hand for efficient transfer. Lastly, surfactants and other additives must be mild to the skin and eyes.
Hair cleansing compositions typically comprise combinations of anionic and nonionic surfactants, however, an ideal cleansing hair care formulation also should contain conditioning fatty cationic actives for improved deposition. Thus, a key focus for good shampoos is the initial proper selection of the surfactant system. As is well-known, surfactants are based on different chemistries and while all cleanse the hair, each offers strengths and weaknesses. Of the more popular key types of surfactants are alkyl and alkyl ether sulfates, olefin (ether) sulfonates, sulfosuccinates, fatty alkanolamides, amine oxides and betaines.
Alkyl and ether sulfates: This class is the workhorse of the shampoo category, with the most notable materials being sodium and ammonium alkyl (or PEG-alkyl) sulfate. In product development, it is important to know that with this class of surfactant, solubility increases as the temperature is increased. Although alkyl and alkyl ether sulfates are generally safe for skin and hair use, they can cause skin irritation if they remain on the skin for too long. They have good foaming characteristics but the foam collapses quickly; thus, this class is typically combined with other foam-boosting surfactants such as the alkylamidoalkyl betaines (cocoamidopropyl betaine), or alkanolamides to increase viscosity.
Olefin (ether) sulfonates: Similar to sodium lauryl sulfonate, olefin (ether) sulfonates are the second most widely used surfactants in shampoos. They have similar foam characteristics to alkyl and ether alkyl sulfates, more water solubility (high concentrations) than sulfates, and are more stable over a wide pH range.