As the dye oxidises, it expands, giving you George Washington hair. At first I enjoyed this, because I am still a poor plebe who hasn't seen Hamilton yet, and I got to re-create the show via my own colonial-esque look.
But then I started to feel the weight of the dye on my head, which hurt a lot. Everyone's different, but for me, my neck cramping felt way worse than any itchiness I was experiencing.