zh-hans:湿 肥皂是一种用作个人清洁用品的表面活性剂，通常以固体块状的形式存在。

古代不管是东西方，最早的洗涤成分不外乎都是碳酸钠和碳酸钾。前者为天然湖矿产品，后者就是草木灰的主要洗涤成分。

肥皂的发明据传是地中海东岸的腓尼基人。有传说指，公元前7世纪古埃及皇宫中的一名腓尼基厨师可能是发明了肥皂的人：

然而据至目前为此的考古发现，类似肥皂的物品可以追溯至西元前29世纪的古巴比伦。而西元前23世纪时，在巴比伦的泥板上已有记载制造肥皂的公式。虽然肥皂很早就被发明，但块状肥皂却是奢侈品，直到十九世纪才广泛被一般大众使用。

In chemistry, soap is a salt of a fatty acid. Consumers mainly use soaps as surfactants for washing, bathing, and cleaning, but they are also used in textile spinning and are important components of lubricants.

Soaps for cleansing are obtained by treating vegetable or animal oils and fats with a strongly alkaline solution. Fats and oils are composed of triglycerides; three molecules of fatty acids attach to a single molecule of glycerol. The alkaline solution, which is often called lye (although the term "lye soap" refers almost exclusively to soaps made with sodium hydroxide), brings about a chemical reaction known as saponification.