No.4 and No.5 are both formulated with patented OLAPLEX Bond Building Chemistry to restore, repair and hydrate hair without adding excess weight. They reduce damage and frizz for strong, healthy and shiny hair. Like the rest of our range, Olaplex No.4 and No.5 are totally non-toxic, sulfate free, paraben-free, vegan, gluten free, nut free, and color safe.