In the broadest sense, a detergent is a cleansing agent of any kind. The term has become commonly used in a narrower sense to describe particular chemical cleansing agents developed in the twentieth century. These detergents replaced soap and washing soda as the preferred agent for washing clothes.

Soap is made by mixing animal or vegetable fats with sodium hydroxide (caustic soda) or potassium hydroxide (caustic potash). This causes the fatty acids to form sodium salts. In its normal bar (tablet) form, soap is not ideal for washing large loads of clothes. For centuries, the usual practice was to presoak clothes in water to which lye, an alkali derived from wood or plant ash, or urine had been added. This had a mild bleaching effect and loosened dirt, which could then be removed by rubbing with soap. In 1791, a French chemist, Nicholas Leblanc, developed a process for making washing soda (sodium carbonate), which performed the same function as lye or urine. In Britain, most people used soap very sparingly until 1853, when the government repealed a soap tax imposed in 1712. The first powdered soap, Babbitt’s Best Soap, went on sale in New York in 1843. The first British soap powder was Hudson’s Soap Extract, introduced in 1863. By 1900, soap was also available in flake form. In 1918, the British company Lever Brothers (now Unilever) introduced Rinso, the world’s first granulated laundry soap.

The German company Henkel took the first step toward modern detergent technology with its Persil washing powder, introduced in 1907. The name was derived from two of its constituents, perborate and silicate. Perborate releases oxygen from the water molecules so that it becomes available to act on stains. Persil was an improved soap powder, rather than a modern detergent, but its self-activation process was the key to the successful laundry detergents that followed. The U.S. company Procter & Gamble developed an equivalent product, Oxydol. After electric washing machines became available in 1907, the disadvantages of soap-based laundry products became more evident. When soap is used in water containing magnesium and calcium (hard water), insoluble salts are created, which form scum on the surface. The first nonsoap detergents were developed in Germany in the late nineteenth century, with coal tar as the base and sulfuric acid as the reagent. Nekal, introduced in Germany in 1907, was the first detergent to be marketed commercially.

However, although early detergents eradicated the scum problem, they were not as effective at washing clothes as the improved soap powders. In 1933, Procter & Gamble marketed its first detergent, Dreft, as a cleanser for washing dishes in hard water. It launched the first synthetic laundry detergent, Tide, in 1946 as the “washing miracle.” Tide became the leading American laundry detergent in the 1950s. The British equivalent of Tide was Surf, introduced by Unilever in 1949. These new detergents contained optical brighteners, which enhanced the appearance of white clothes. Previously, a similar effect had been achieved by adding a blue powder to rinsing water. From the 1950s, powder detergents were based on alkyl benzene, a light, clear oil derived from coal tar or petroleum. In 1968, the first biological detergents appeared. These contain enzymes, which are natural catalysts with specific properties. The digestive enzymes used in detergents break down biological stains: lipase acts on fats, protease on proteins, and amylase on starches. Another advantage of enzymes is that they are effective at low temperatures. The increasing popularity of front-loading automatic washing machines created a need for low-lather detergents. Silicone is one of the ingredients that can be added to reduce foaming. In the mid-1980s, liquid detergents were developed.

While advances in detergent technology improved their washing performance, it became apparent that a number of the key ingredients had damaging environmental consequences. Phosphates and surfactants, the surface-active agents that improve wetting (the penetration of water into fabrics), evade the biological processes used to purify sewage. Phosphates, which may also be found