It approximately last for about 2-3 months. But your treated hair maintains their vitality depends on what you do with them during this period.
Here are some useful tips:
i) Wash Less
ii) Use a dry shampoo
iii) Top-up your hair with a Keratin shampoo.
iv) Use sulphate-free orgic shampoo.
v) Avoid swimming as chlorine water could harm your hair.
These tips would help to preserve Keratin in your hair for a longer time.