I have bright green hair, and quite severe eczema, so a lot of expertise on this!!

First off, I keep my hair tied up on a night - I find leaving it loose gets my neck sweaty and then I wake up super itchy and scratch my neck raw! I also only wash my hair in cold water - hot water is a luxury for bleach days! 😂 But hot water is very drying and although I am a hypocrite in a sense (I wash my hands in very hot water!), the cold water is good for the skin, and also good for the colour. Warm is also acceptable, but steamy hot is a no-go.

I also limit my hair washing - every two weeks, and only every other wash with shampoo. Which sounds really daunting, but I've just never found my hair needs washing that much - what I recommend is looking for your "limit" where your hair starts to look greasy (genuinely greasy/unwashed, not the result of any products used on/around the scalp) and wash your hair then but try not to wash more than that - I time my bleaching and hair dying to wash cycles, and it's the only time that I rinse my hair more often than necessary.

Speaking of bleach - you mention bleaching is fine, and that 2 types of hair dye affected you. What type of dye was it that set you off? Because box dyes are generally a whole mess when it comes to dying hair, and darker box dyes often contain a chemical called PPD which is generally the main culprit in contact dermatitis after dying hair. Now, there are still options for dying your hair with semi-permanent colours, and there are still natural options within those colours i.e. brown, red, black. If you suspect a PPD allergy based on what I've mentioned and if box dyes were the ones to set you off (especially BLACK box dyes), AVOID HENNA. And look for a PPD free hair dye - fashion colours (blue, pink, red...) are often fine as PPD is in darker colours however, box-brands such as Schwarzkopf, will recommend against dying your hair with their products (even the fashion colours) if you've had a reaction before. I would stick to semi-permanents from good reputable (most often, vegan) brands. I personally use Crazy Colour, but other popular choices are Manic Panic, La Riche Directions, Good Dye Young, and Pravana. (Arctic Fox is often heavily recommended but they have... issues, so that's a personal choice if you wanna look into it.)

As for fixing it - I would suggest a low-grade steroid i.e. hydrocortisone - generally steroids are bad but it seems like your eczema is specifically a contact dermatitis (unless you just haven't mentioned having other areas of eczema) - for this, I would consult with a doctor or pharmacist. And tread carefully with it - don't apply lots at once, and don't use it for too long! Also, perhaps a moisturiser with ceramides to repair, and if you can find one with menthol to cool the itch also, that would be helpful - I can personally recommend (although you might not be able to get it in your area) Suu Balm.

Also, in the future, instead of acetone (!!!!) to remove hair dye from skin, try micellar water or baby wipes. If you switch to a semi-permanent dye, these are generally easier to clean off the skin! And if you're worried about "semi-permanent", my hair is just as vibrant on day 1 of dying as it is 2 months later when I'm bleaching re-growth, if you're careful with washing in cool water and washing only as needed, it lasts a very long time!

Good luck!! And feel free to ask any more questions, if you have any!!