Because pure water can not remove oily, organic soiling detergents, soaps are used for cleaning. Soap cleans by acting as an emulsifier. Basically, soap allows oil and water to mix in such a way that oily grime can be removed during rinsing. Detergents were developed in response to the shortage of the animal and vegetable fats used to make soap during World War I and World War II. Detergents are primarily surfactants, which could be produced easily from petrochemicals.

Surfactants, also known as wetting agents, lower the surface tension of a liquid, allowing easier spreading, and the interfacial tension between two liquids. The term surfactant is a contraction of "Surface active agent". Surfactants are usually organic compounds that are amphipathic, meaning they contain both hydrophobic groups (their "tails") and hydrophilic groups (their "heads"). Therefore, they are typically sparingly soluble in both organic solvents and water. Surfactants reduce the surface tension of water by adsorbing at the air-water interface. They also reduce the interfacial tension between oil and water by adsorbing at the liquid-liquid interface.

Modern detergents contain more than surfactants. Cleaning products may also contain enzymes to degrade protein-based stains, bleaches to de-color stains and add power to cleaning agents, and blue dyes to counter yellowing.

Surfactants are toxic especially to fish and should be monitored.
With enzyme-linked immunosorbent assay (ELISA) method the amount of surfactants in water and other matrices can be determined. Ideal instruments for ELISA formats the multimode readers Mithras LB 940 and TriStar LB 941.