Just wanted to share my experience in case it helps any one.
Essentially, eliminating sources of capsaicin from my diet (including black pepper, cayenne pepper, paprika, chilli powder), milk, and sulphites has kept me eczema-free for 2-3 years.
Itching for me starts approximately 48 hours from the time I take the problematic food/drink. It was years before I realised that. And since then it has taken a lot of time to identify foods that cause itching.
I used to have eczema sometimes as a child. Fast forward to age 18 and this flared up very badly on my face, above eyes, forehead, neck, for months on end. I later realised this coincided with unknowing continued exposure to food with low-level traces of milk (Whittards white bread). I am allergic to milk protein and intolerant to lactose. Because of the time delay with symptoms, it was hard to trace. However when I eliminated this from my diet, my eczema improved. I became more careful and eliminated all types of food with any sort of trace of milk and my symptoms pretty much disappeared.
However every so often, eczema would still flare up. With the 48 hour time delay for symptoms it has taken time to identify the additional problematic foods I have eventually pinned this down to foods containing sulphites (vinegar, wine, any foods containing sulphur dioxide including some tinned & jarred goods), and foods containing capsaicin (chillis, hot peppers, and even foods containing lots of black pepper, which contains the same chemical capsaicin found in chillis).
Eliminating these three groups of foods has eliminated eczema from my life (and incidentally all associated 'bad stomach' symptoms). When I look back it has changed my life hugely for the better. I love(d) chutneys and used to sprinkle black pepper liberally on foods. I also love(d) a lot of foods which these days thanks to new legislation list 'may contain traces of milk'. I sometimes try these to see if my body has 'got over' these things. However each time I eventually realise it is not worth it; the symptoms come back and it is just not worth it.
I'm sure this diet change is not a blanket cure for everyone. I have food intolerances and allergies and my eczema seems to be very much linked to that. Others will have different underlying reasons for eczema. I have posted this here in the hope that someone else might find this type of diet avoidance treatment helps their eczema.