Possible bleach allergy?

Hi guys, I'm looking for a bit of guidance.

Also I've never dyed my hair or anything before so forgive me for not knowing what I'm talking about!

Basically I wear my hair in a weave and for the last 2 years I've used bright red hair extensions, which I buy already in that colour. But over the last year I have developed progressive allergy symptoms which in the last couple of months have become unbearable, symptoms including eye swelling/eczema and very bad inching all over. There is obviously a good possibility that I am allergic to something in the hair, but I do also have a condition that potentially makes my body produce more histamines so it may be that also. I'm going to have tests done at a dermatologist in attempt to find the allergen but in the meantime I really need to install a new weave. This time round I've bought virgin dark brown hair extensions to avoid allergies. But I really rather have coloured hair so I did also buy a natural henna based red hair dye which is supposedly free of the common allergens. Though of course I would need to bleach the hair first for the colour to show, and I can't know if what I'm allergic to is something in the dye of my previous extensions or the bleach that was used.

So I guess my first question is if anyone knows anything about bleach allergies and if it is actually possible that that could be what I'm allergic to? I didn't actually think bleach stayed in the hair but I read that it does? Also if there are any other safer options to lighten hair? I'm also thinking of doing a bleach patch test myself (I will for the henna dye too), could someone tell me how to go about it?

Thanks!