Back in times 1917 , my grandmother made her own old fashioned soap using lye, called potash, wood ashes, and water. Grandma would combine it with the fat rendered from butchered animals and boil the mixture over an outdoor fire for many hours or days until a soft soap was formed. While this was a natural and admirable way to make soap, it was also labor-intensive and difficult to control the quality of the final product. Modern times have brought about man-made substitutes to replace the wood-ash solution. Sodium hydroxide (also called caustic soda or lye) is commonly used to create solid bars of soap. With these standardized ingredients, the guesswork has been removed and soap crafters can reliably produce batch after batch of gentle, balanced soap. Grandma's Pure Lye Soap Bar - Unscented Face & Body Wash Cleans with No Detergents, Dyes & Fragrances Free of chemicals that cause allergies and serious itchy skin problems Lye Soap is great for men and women with dry sensitive skin but works great for all skin types. Saponification is an exothermic chemical reaction—which means that it gives off heat—that occurs when fats or oils (fatty acids) come into contact with lye, a base. In this reaction, the triglyceride units of fats react with sodium hydroxide or potassium hydroxide and are converted to soap and glycerol. For some types of soap, salt is then added to precipitate the solid soap.