This professional-only repair treatment is the first step of the revolutionary Original Bond Building system offered as a single step so you can restock at your own pace. No.1 is an easy add-in to any color, lighten, and chemical services to help prevent and repair damage as it happens. No need to change the formulas or measurements of your chemical services. Unlike built-in bonders, N°.1 seamlessly works at a molecular level in your chemical services to rebuild all three bonds, including disulfide bonds, for stronger, visibly healthier hair. Follow up with No.2 (sold separately) after the service to reinforce repair.