If dry, damaged hair is your main concern, the No. 0 Intensive Bond Building Hair Treatment is a must-have. This powerful addition to the OLAPLEX lineup features the highest concentration of their patented technology in any at-home product. Designed as a two-step process, No. 0 acts as a primer for No. 3, enhancing the effectiveness of both treatments to rebuild hair bonds, strengthen, and protect your hair. While it can be used alone, the combination of No. 0 and No. 3 shows the best results. The key ingredient, bis-aminopropyl diglycol dimaleate, works to restore and repair chemically-treated or heat-damaged hair. Suitable for all hair types and textures, this treatment is especially beneficial for severely damaged hair and improves with regular use.