- An anionic surfactant is a macromolecule, usually in the sulfonate or sulfate group of chemicals such as sodium laureth sulfate, that acts as an active surface agent to lower the surface tension of liquids. This allows them to bind to impurities and particles that are suspended in the liquid, which makes them effective cleaning agents in water. In small concentrations, they can also cause the foaming of compounds in water by creating large numbers of small bubbles of gas, and this makes them effective in cosmetics such as shampoo, toothpaste, and in fire-suppressing agents.
- Basic soap used to clean the human body is also a type of surfactant or detergent made from natural fatty acids of plant or animal origin. The difference with an anionic surfactant is that it is largely a synthetic chemical, and it has been designed to act not only as a surfactant that binds to oils and particulates in water, but also as a denaturing chemical for proteins. Since anionic surfactants break down proteins attached to clothing in water, they are not recommended for ordinary soap use, as human skin is also a type of protein.
- Chemical engineering has been perfecting anionic surfactant synthetic detergents since the late 1940s when they began to replace ordinary soap for washing machine use. The negative electrical charge of their ionic nature makes them bind to dissolved minerals in hard water. Ordinary soap will leave an insoluble, gray-colored film on materials that are washed in hard water. Early surfactant detergents were based on alkylate compounds, and the drawback to their use was that they are carried out to natural waterways in the waste water systems of cities where their foaming ability prevents breakdown by natural microorganisms. These compounds were made illegal by 1965 in most nations, and a switch to related alkylbenzene sulfonate (LAS) chemicals alleviated some of the issues with water pollution.