Brand from United States: OLAPLEX. Prime your hair for your deepest at-home repair with this salon-inspired pre-treatment to boost the effects of N°.3 Hair Perfector™. The highly concentrated formula rebuilds disulfide bonds to repair more severe damage and immediately strengthens hair when N°.0 is used with N°.3.How to use:On dry hair, apply and distribute evenly from root to tip. Leave on for 10 minutes. Do not rinse.Apply N°3 Hair Perfector™ and comb through. Leave on for 10 minutes. Rinse well.Shampoo and conditioner with N°4 and N°5.Use as a two-part system with N°3 once a week or 2-3x per week for very damaged hair.