Shampoos are made of a class of chemicals called surfactants, which have the ability to lower the surface tension of a liquid. These surface-active substances surround oily substances and dirt, which then makes it easier for water to wash them off the surface that needs to be cleaned. This ability to act as degreasers makes surface-active substances popular for cleaning applications and products like shampoos.
Although shampoos are made mostly out of water, it is the 10 to 15 percent concentration of various surfactants that is responsible for the cleansing action. A few examples of specific surfactants are sodium lauryl sulphate, used in medicated shampoos, and ammonium and pyridinium cationic surfactants, which are used to fight bacterial infections and in the cleaning of open wounds.
The other characteristics of shampoos, such as the foaming ability and general smoothness, come from elements called foam boosters and conditioning agents. Because some surfactants are rough on the skin, a conditioning agent is necessary to soften the effects. These are silicones, polymers and quaternary agents with various long chemical names. Foam boosters are alkanolamides or betaines, which are made of fatty acids and are soluble in both water and oil. They are responsible for the bubbles and the spreading ability of the shampoo.