A water-dispersible cleansing and emulsifying agent produced by the saponification reaction of long chain fatty acids, such as found in oils and fats, with an alkali, such as sodium hydroxide or lye. Soaps made from animal fat and wood ashes have been used since antiquity. Although soap was made at home for laundry purposes from the European Middle Ages to early modern times, cake soap was a luxury product that came into common use only in the 19th century.