I've just got to scratch.

I had this same issue with having my hair dyed at the hairdressers. I took a Piriton before my last few appointments for dye and that sorted the itching. I decided it was just not worth the risk and I am now very happily enjoying having grey hair.

In the pandemic I have used box colours on my grey roots, and my scalp became itchy, dry and sore. Could anyone suggest a hair colour which will not irritate the scalp? I’m reluctant to go to the hairdresser until I’ve had the vaccine. Thanks.

I used to have my hair coloured regularly at the local training college by students training to be hair stylists and before each time, I had to have a skin test of the product to be used. I doubt if this is done in hair salons before each time for regular customers, but may be worth popping in and asking them to do a skin test - I think it was on the inside of elbow, or wrist - a week before your appointment.
I have now gone back to natural - some grey, some dark - and also back to my natural curls, following some of the Curly Girl methods - drying naturally and not combing/brushing after washing. Makes a huge difference to the curls!

The last time I dyed my hair - a few years ago now - I used Movida (it was quite new on the market then). I developed an itchy bit of scalp down near the nape of my neck. Eventually had to go to doc, and was given Betnovate. A year or two after that I read that a woman had died whilst using Movida. She had an extreme allergic reaction. So, I stay grey. Which is fine by me.

What does your hair dresser advise? The new hair dyes seem so much less likely to trigger this kind of thing. Are you sure it's a reaction to the dye and not something horrible like scalp psoriasis? It may be worth asking your GP to have a look.

Henna is a 'vegetable dye' if that phrase means a dye made from a plant. Just saying because of the juxtaposition of "I am allergic to henna" and "vegetable dyes are available".

I'm naturally grey now, not all but probably mostly. I left it for a while being grey but then felt really old like that so decided to go back to the bottle! I went back mid blonde and over Christmas I've been a mahogony colour from the Live range. I love it and it is a nice change and why not? I once went purple out of Live range and that was nice too. I might go bright pink for summer.

I'm just updating on the itchy dry scalp. I think I've found the culprit. The clue was reading back my post. I buy shampoo regularly but hardly use any conditioner so a bottle can last years. The stuff I've been using must be at least fours years old. I think it may be 'on the turn' stuck for that long in a damp humid bathroom. Perhaps this was aggravating my dry scalp. It's much better now. It's still dry but not as itchy or sore. I know dying my hair doesn't help but I'm very reluctant to go grey, at least over night. Vanity I know. I keep telling my hairdresser I'll go grey when I retire but I don't think they believe me. I'm not sure I do either. It's the thing I miss most as I age my lovely dark mahogany hair...sigh

You must be allergic to the hair dye. You should stop. It could be dangerous. Sorry to be blunt, but that's just not good.

Sorry I meant Betnovate shampoo

It used to happen to me, just the same. I saw my GP, who is a dermatologist, and he said I had psoriasis on my scalp. I stopped dying my hair - not that he said I should, but I just thought it was probably a sensible thing to do. It hasn't cured the psoriasis, obviously, but once all the colour had grown out I have to say I felt totally liberated, completely free of the tyranny of the bottle

When this happened to me the pharmacist suggested changing my shampoo - it worked.

You could try Benovate shampoo my worry is that you are allergic to what's in the dye. I'm allergic to henna. Vegetable dyes are available. You could ask your hairdresser to do patch tests of different hair colours.
good luck