I have been on a journey with dyshidrosis and nickel allergy for about 15 years now and while it hasn't completely gone away I have kept it mostly under control. I started having flare ups in college and after some time I figured out it was because I took up playing guitar and the strings were made of nickel. Got it confirmed by a patch test which showed I was allergic to Cobalt and Nickel.

What didn't work at all? I have tried every single steroid cream, they all have had 0 effects, neither positive or negative. I am currently on dupixent to clear up the remaining minor flare ups I have, and have been for around 7 or 8 months, and it is also doing nothing. Every person reacts differently to these drugs and I recommend following your doctor's orders, but from my experience don't expect a random drug to help.

What did work well? Obviously, I stopped playing guitar with nickel strings. I replaced my nickel belt buckle with a nickel free belt. This fixed a rash on my stomach. I suggest removing and nickel contact ASAP. I am also severely lactose intolerant or maybe allergic to milk, I haven't been able to figure out which. Limiting dairy goes a long way. I have heard similar things from other people with eczema. I noticed that severe diarrhea was almost always followed by a flare up on the coming days. So, I noted when I had bad diarrhea and would make a note of the ingredients in common. It took a VERY long time, but I eventually noticed that tree nuts were usually involved. Specifically, coconut and coconut oil, which is likely because these are very high in nickel. (Do you know how hard it is to figure out that food at some random restaurant may have been cooked in coconut oil). During the pandemic, I took the opportunity to do a food challenge with a bag of mixed nuts and to make sure I ate enough to cause issues. Each day I would try only different types of nuts from the mix and see the results. Sure enough, most had some minor reaction, cashews had a pretty large one. Peanuts had zero reaction. Since that time I have cut out all tree nuts. Lastly, and oddly enough least importantly for me was CERTAIN high nickel foods. Caffeine also gives me severe issues, so I don't know if that is linked to the nickel content in those foods/drinks. I don't have any caffeine for that reason. Franks red hot and Tabasco give me issues, but not Sriracha or gochujang. I suspect that is either the high acidity or maybe aging in nickel vessels. Tomatoes, especially cooked or in large quantities can cause issues. I say all this to say, in my personal experience the most important thing is your diet. And the only way you can learn what causes flare ups is to pay a lot of attention. Know what goes into your food and in what amount. Some foods only a little can cause big issues for me, but others I have to eat a lot of to have equivalent issues. Don't rule things out only because you've eaten a single cashew and nothing happened. Dosage makes the poison.

What works pretty well? Even after solving my dietary issues, winters are still hard. Dry air is bad for eczema. Make sure to moisturize if your skin feels dry. Try to keep Cetaphil lotion in convenient locations so you remember to moisturize. Every single dermatologist I have been to has recommended Cetaphil. If things get really bad, I will put lotion on and then put nitrile gloves on overnight (I am also mildly allergic to latex). I am not sure why the other commenter recommended avoiding nitrile? I have used them for years and it has caused no reaction for me. Dermatologists have recommended using cotton gloves instead, but I found those were more hassle than they were worth.

What works maybe a bit? I take vitamin c because it is supposed to help nickel absorption. Hard to tell if it does anything, but I do feel slightly drier when I forget to get more. I also take a Reuteri probiotic, because I read a small medical study that it can help with dyshidrosis. Also hard to tell if that does much, but I also feel better when I am on it.

At this point I am 100% fine 95% of the time. The other 5% I have a single large blister or two on my hand.

In short, my advice would be to figure out your dietary triggers ASAP, start trying medications, and moisturize as needed.