From Wikipedia - -
Castile soap is a name used inEnglish-speaking countries for olive oil based soap made in a style similar to that originating in the Castile region of Spain.
Castile soap is THE most gentle soap you'll find. Eco-Logic Castile soap is made with 100% Pure High Quality Olive Oil, Sodium Hydroxide (substance used to turn oils into soap), and water. Three ingredients are slowly blended together, in the old fashioned soap making process (which retains the naturally produced vegetable glycerin) for the most gentle,vegan soap. (Keep out of the flow or pool of water to extend it's life). Castile soap is perfect for baby, new mom, or anyone that suffers from ultra-sensitive skin. You simply won't find a more gentle soap.