Soap

Soap is a salt of a fatty acid used as a surfactant for cleaning. It is typically produced by saponification, a chemical reaction between fats or oils (triglycerides) and alkali such as sodium hydroxide (lye) or potassium hydroxide. The resulting substance consists of sodium or potassium salts of fatty acids and glycerol. Soap cleans by reducing surface tension and allowing oily dirt to emulsify in water.

Production methods include the cold process, where triglycerides are mixed with alkali and allowed to cure into bars, and the hot process, which uses heat to speed the reaction. Hard soaps are sodium salts used in solid bars, while soft soaps or liquid soaps are usually potassium salts. In handmade or artisanal soaps, glycerin is often retained, whereas some commercial formulations remove it to improve shelf life and clarity.

Properties and limitations: soap works best with soft water; in hard water, calcium and magnesium form insoluble scum, reducing effectiveness. Additives such as fragrances, dyes, and moisturizers are common. Glycerin acts as a humectant and can contribute to moisturizing effects in gentler formulations.

Uses: soap is widely used for personal cleansing, laundry, and industrial cleaning. It serves as a detergent in various applications, including lubrication, degreasing, and hygiene products. Environmental impact is generally favorable, as most soaps are biodegradable, though formulation and manufacturing practices influence ecological effects.

History and terminology: soaps have been produced since ancient times, with early references in multiple civilizations. The term soap is thought to derive from Latin sapo, with cognates in several languages.