I suddenly got a reaction to hair dyes a couple of years ago after having a tattoo done.
It started with itching whilst the dye was on to my glands in my neck swelling, my eyes swelling and blisters on my scalp and ears where the dye touched.
Being the vain thing I am, lol, and trying to cover the ever impending grey hairs, I've experimented with different brands.
My conclusion, for me anyway is , that I only use cheap dyes. The more expensive home dyes set my allergy off big time, I'm assuming because the amount of whatever chemical it is that affects me.
I only use Aldi's own brand hair dyes now, I have hardly any reaction at all with them.
I've looked into henna dyes, but apparently they can give you a reaction too.
My worst reaction was when I dyed my hair 2 days before Halloween last year- I ended up with swollen eyelids- my Dc's thought it added to the dressing up for Halloween Theme