This intensive, at-home pre-shampoo treatment is designed to repair and strengthen all types of damaged hair. It works by rebuilding the hair's disulfide bonds, which become broken or damaged through chemical processes, heat styling, and mechanical stress. For best results, use as a first step before Olaplex No.3. This powerful formula primes the hair to maximize the reparative benefits of your subsequent treatments, leading to visibly healthier, stronger, and more resilient hair structure.