I have wondered this before, and almost posted this question in the past, but this thread now has me wondering again. If you use any kind of over the counter hair colorant, they are plastered very blatantly with warnings about possible blindness.
So I want to know, through what mechanism do hair coloring products cause blindness? When I searched the Internet myself, all I could find was the story of two women in the 1930s that had an allergic reaction that ended in blindness. There must be morons out there disregarding the labels – what is happening to them? Is it a proven chemical reaction? Is it allergies? I don’t plan to disregard the warnings, but I would like a more detailed reason than “because we said so” - one that strikes the fear of science in my heart.