What is soap used for?

It is a traditional washing product commonly used in every family.

Soap is generally a solid block product, but there are also paste and liquid products. The object of soap is different from laundry soap, which is generally aimed at human skin, such as washing hands, washing face and bathing. With the improvement of people's living standards, it is required not only to have the function of cleaning skin, but also to have some new functions such as skin care, beauty, sterilization and deodorization. Traditional cold soap and hot soap are both fatty acid soaps with fatty acid salts as the main surfactants. The pH value of fatty acid soap is alkaline and it has strong deoiling ability. After washing, the skin feels tight. Long-term use will make the stratum corneum thinner, which is irritating and harmful to the skin. When used in hard water, it will react with calcium ions to form insoluble calcium soap. A synthetic detergent appeared in Song Dynasty, which was made of natural Gleditsia sinensis (also known as Gleditsia sinensis, hanging knife and Gleditsia sinensis) by mashing and grinding, adding spices and other things, and made into orange-sized balls for washing face and bathing body, commonly known as "soap balls". Song people's careful "Old Wulin Stories" (Volume 6) and "Little Broker" recorded that there was a businessman who specialized in "soap troupe" in Lin 'an, Kyoto in the Southern Song Dynasty.