I had a dog with severe allergic reaction to something he was eating.
Unconfortable isn't the word!
He spent 18 months on steroids, but it never stopped the itch and in the end I stopped them, as the dose was needing to be increased.
I did an elimination diet and it turned out he was allergic to ....
meat protein !
He did amazingly well on a vegetarian diet based on peanuts and chickpeas :-)
Sadly in those days, there wasn't the internet :-) or even computers! And when the vegetarian diet became unavailable he ended up back on dog food. But he then needed Piriton daily to keep him from scratching himself raw :-(
I had wanted to make his diet myself, but in those days took the vet's advice not to try this as 'dire things would happen'. These days, having more experience, and more information available, I'd ignore the vet and feed a home made diet.
Yes, the allergy tests can be hit and miss, but an elimination diet, though it can take some time, can help pinpoint the offending items.