Hi, - this doesn’t affect me, so have no personal experience, but just thought I’d pass something on which I heard yesterday and as it sounds quite feasible, and might just help someone who‘s dog has allergies......
A friend‘s dog has been suffering from a food related allergy which the vet suggested could be caused by mites which can often be discovered in bags of dried food! He suggested freezing the food beforehand, which she‘s been doing and apparantly its done done the trick!
Its possibly a one off, I don’t know what the food was or how or where it had been stored but when all other options have been exhausted, it might just be worth considering!