Question: how long do you leave permanent hair color on?
Answer: Most hair dyes should be left in the hair for a minimum of 30 minutes, and no longer than 45 minutes. The hair dye needs 30 minutes for the ammonia and peroxide to work its way into the hair cuticle to change the hair's natural pigment. The last 15 minutes are for the dye to fully develop and permeate the hair.