If he has grain allergies, your first step is to stop washing him with a grain. Try Zymox, or Duoxo shampoos. Coconut oil for topical will see more relief then any of those hotspot sprays. It's also all natural and a natural antibacterial. Also rotating fish oil and coconut oil in his food will help as well. And if he has contact allergies to grass or other outdoor everything you can use a 50/50 water apple cider vinegar with the mother to wipe him down when he comes in from outside.
What protein is in his kibble? If it's chicken, try switching to a fish protein.
"i can explain it to you, but i can't understand it for you."