Just some other preventative suggestions.
Always make sure the water and food bowls are clean. I clean the bowls after every single meal even if I can't see anything.
Wipe down the muzzle after every meal and drink. Paying particular attention to the folds of skin by the eyes and under the chin.
I didn't do these things as much as I should have when he was a pup and there was some irritation. Since then I have been much better with it and no issues.
Not saying it would be a cure if he has allergies, but its a really good habit to get into, imo