OLAPLEX Nº.4P strengthens, softens, and neutralizes unwanted yellow tones for brighter, more manageable hair. The sulfate-free, highly concentrated formula allows for customizable toning -- the longer you treat, the brighter the results. It contains our patented technology to repair, hydrate and brighten while being gentle enough to use as often as needed. Natural or stylist-created, root-to-tip or balayage, every client can benefit using this as part of their Blonde Maintenance Routine for the best blonde yet.