Like when treating humans, in dogs, allergy symptom relief is often medicated using antihistamines, or steroids in more severe cases. These medications can provide momentary relief from the symptoms of the allergy, but they will not address the core cause of the issue. Meaning, if your dog is once again exposed to whatever he is allergic to, then allergies will flare-up again.
For food or flea allergies, it is best to prevent the allergy before any flare-ups occur. It is important to have an all-year-round flea prevention routine so that these allergies do not happen. However, if you suspect that your pet is allergic to a certain food type, identifying which food type it is can take some time and is very challenging. The trial and error method on food your dog eats is normally used to eliminate which specific ingredient your dog is allergic to.
Have regular communication with your veterinarians London ON, and keep them involved in trying to identify what your dog is allergic to.