Question: how long do you have to wait to use purple shampoo?
Answer: If you have never used purple shampoo before, try leaving it in for 5-10 minutes and washing it off. If you notice little or no difference in color after drying your hair, try 10-15 minutes for your next treatment. If you leave the shampoo on longer than 15 minutes, expect lilac tinting to be left in your hair.