First things first, shampoos do not feed, resuscitate, enliven or revive hair. They can’t, for the simple reason that hair is not alive. It is a shaft of dead proteins, notably including a tough fibrous material called keratin that also shows up in fingernails.
So what CAN shampoos do?
They can clean hair, a task not too difficult. All that is required is removal of the thin layer of oily material known as sebum. Produced by sebaceous glands in the skin, it coats and protects the hair. Unfortunately, sebum also acts as a virtual magnet for dirt and residue from hair treatment products.
Common to most synthetic chemical shampoos is an ingredient called a surfactant, that is the same used in your washing-up liquid, and it has the ability to reduce surface tension of water so that a droplet of water will spread out rather than stay in the raised dome shape, i.e. it makes water wet. Other surfactants are repelled by water, but show great attraction for oily substances. The result is that as the hair is rinsed, the soiled sebum is washed away.
Lathering of a chemical shampoo also is the result of the activity of surfactants. Foam is nothing more than dispersion of a gas, in this case air, in a liquid. There is no clear link between a surfactant’s ability to clean and to produce foam. Indeed, a very effective shampoo that does not lather well can be formulated. But would you buy one?
We are used to linking suds and cleaning as belonging together. So most manufactures incorporate surfactants with strong lathering properties although they may not be ideal in terms of conditioning or irritant potential.
The word shampoo was coined from “shampoo,” a Hindi word meaning to massage or knead, and before the advent of synthetic detergents we used soap, and the first shampoos were just solutions of soap prepared from water, soap and soda (sodium carbonate).