All soaps are made by combining lye with oil. The differences in soap is the oils that are used to make it. Each oil produces different qualities. Olive oil castile soap is made using primarily olive oil.
Olive oil is a monounsaturated fatty acid that helps smooth and moisten the skin. Hydroxytyrosol is a very powerful antioxidant found only in olive oil. This oil is non-greasy and won't clog your pores. Very mild and great for babies and sensitive skin.