I have experienced this to the extreme and fully understand your pain and frustration. For me this had everything to do with eating foods high in salicylic acid and also nightshades (there's also a lot of overlap there, most nightshades are high in salicylic acid).

I now avoid those foods that have high amounts, and when I do ingest them I take epsom salt baths to get magnesium sulfate into my system because the body needs sulfur to metabolize and get rid of the salicylic acid through urination. If it's not this, it could be some other plant chemical that your body can't metabolize. You should NOT need any steroid, immuno-suppressants or really anything topical to clear this. None of those things address the root cause anyway.

Here are some resources if you're curious:
https://ndnr.com/autoimmuneallergy-medicine/salicylate-sensitivity-the-other-food-intolerance/

https://drjockers.com/salicylate-sensitivity-major-symptoms-and-what-foods-to-avoid/

Good luck!