It is a completely optional product and not required for olaplex number 1 and 2 to work (steps 1 and 2 done in salon)
Due to bonds being constantly broken down in the hair due to a number of factors- heat styling, bleaching etc , number 3 will maintain the strength and structure of your hair and keep it looking and feeling soft and shiny from the first use. It will continue to link the broken bonds in your strands (broken bonds are the reason your hair is weak and snappy)
It contains the same active ingredient that is in both number 1 and 2 .
Olaplex is free of : silicones, sulfates, phythalates, DEA, aldehydes and is NOT tested on animals.