A professional-inspired treatment that primes hair for deeper repair with the highest dose of patented OLAPLEX technology in any take-home product. It rebuilds hair bonds, strengthens and protects hair integrity. Use as the first step in a two-part system with N°.3 Hair Perfector. Scientifically Proven: 68% more repair & 3x stronger hair* *When used as a two-part system in just one use.APPLICATION TIP: N°.0 bottle should last 3-6 applications, based on hair length and density.