Surfactants cleanse and build foam by acting at the surface between fat and water (surface-active agents or surfactants). They are able of being mixed with water and fat of the skin, allowing dirt to be removed. Based on their cleansing power surfactants are classified into primary and secondary or co-surfactants. Based on the chemical structure there are anionic, amphoteric, non-ionic, and quaternary agents. Surfactants form the base of all personal cleansing products and can also have wetting, conditioning, defatting, emulsifying, & thickening effects. Surfactants are also very useful for homemade soaps (particularly liquid soaps) to improve lathering and decrease harshness. They are added to the oil-lye mixture during the boiling procedure. Surfactants greatly accelerate and improve the soap making process.