A detergent (as a noun) is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning. As an adjective pertaining to a substance, it (or "detersive") means "cleaning" or "having cleaning properties"; "detergency" indicates presence or degree of cleaning property.
The earliest detergent substance was undoubtedly water; after that, oils, abrasives such as wet sand, and wet clay. The oldest known detergent for wool-washing is stale (putrescent) urine. For the history of soap, see the entry thereon. Other detergent surfactants came from saponins and ox bile.
The detergent effects of certain synthetic surfactants were noted in 1913 by A. Reychler, a Belgian chemist. The first commercially available detergent taking advantage of those observations was Nekal, sold in Germany in 1917, to alleviate World War I soap shortages. Detergents were mainly used in industry until World War II. By then new developments and the later conversion of USA aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of household use, in the late 1940s. In the late 1960s biological detergents, containing enzymes, better suited to dissolve protein stains, such as egg stains, were introduced in the USA by Procter & Gamble.
Detergents, especially those made for use with water, often include different components such as:
Sometimes materials more complicated than mere mixtures of compounds are said to be detergent. For instance, certain foods such as celery are said to be detergent or detersive to teeth.
There are several factors that dictate what compositions of detergent should be used, including the material to be cleaned, the apparatus to be used, and tolerance for and type of dirt. For instance, all of the following are used to clean glass. The sheer range of different detergents that can be used demonstrates the importance of context in the selection of an appropriate glass-cleaning agent:
Sometimes the word detergent is used to distinguish a cleaning agent from soap. During the early development of non-soap surfactants as commercial cleaning products, the term syndet, short for synthetic detergent was promoted to indicate the distinction. The term never became popular and is incorrect, because most soap is itself synthesized (from glycerides). The term soapless soap refers to a soap free liquid cleanser with a slightly acidic pH. Today, soapless soaps are used in an array of products. There is no universally accepted term for detergents not made of soap other than soapless detergent, non-soap detergent or soap-free cleanser.
The term detergent by itself is sometimes used to refer specifically to clothing detergent, as opposed to hand soap or other types of cleaning agents.
Plain water, if used for cleaning, is a detergent. Probably the most widely-used detergents other than water are soaps or mixtures composed chiefly of soaps. However, not all soaps have significant detergency and, although the words "detergent" and "soap" are sometimes used interchangeably, not every detergent is a soap.
The term detergent is sometimes used to refer to any surfactant, even when it is not used for cleaning.