The primary function of the shampoo is to cleanse hair and scalp. In addition to this, it must also respond to other needs, for example:
- to leave the hair soft and shiny, through a selective process that leaves a small dose of sebum on the stem and on the scalp,
- facilitate untangling and styling,
- be easy to apply and not irritate the eyes.
Generally, the SAL (active cleansing substance) of a shampoo is between 8 and 15% and its composition is characterized by the presence of a primary surfactant, generally anionic, such as sodium laureth sulfate, to which one or more secondary surfactants are added .
For this purpose, amphoteric surfactants, such as betaine, are very used, which reduce the aggressiveness of the primary and assist in its washing action. Hydrophilic polymers such as cellulose or xanthana rubber can be used to increase viscosity and to stabilize the product during shelf-life.
Viscose a shampoo is a strategy necessary for "marketing" reasons, since a viscous shampoo conveys the idea of a richer and more powerful formula, as well as making the product easier to escape from the container.
A proper preservative system, a fragrance and, possibly, a dye must not be missing.
The choice of perfume is rather laborious and delicate as it must satisfy more than one need: the fragrance inside the bottle, the one at the time of use and the residual one after rinsing and drying.
As for the active ingredients, numerous plant extracts can be included in this category of detergents, such as nettle, chamomile, birch and mallow, although, more often than not, the addition of these products is linked more to marketing reasons that to the real effectiveness of the extract itself, since they are often used at very low dosages and remain on the skin and hair for too short a time to perform a cosmetic action.
Particular attention, in the case of anti-dandruff preparations, is to be placed in the detergent base, which must be as delicate as possible to avoid irritation or rebound due to excessive degreasing.
The shampooing procedure is always present, to which purpose opacifiers are used, such as glycerylmomostearate or long chain alcohols (cetyl and stearic) or, when a milky appearance is required, polymeric and carboxyvinyl emulsions.
The pH of a shampoo is generally between 5 and 7.
