An allergy is a result of a dog's immune system over-reacting to a stimulus in it's environment or diet. The response to an allergen (pollen, dust, shampoo, vaccine, fleas, etc.) can be acute, life-threatening, or chronic.
An acute but entire body response is called anaphylaxis or anaphylactic shock and can occur from such stimulus as a bee sting or vaccination. These are the most serious reactions and acquire immediate veterinary care.
Sometimes Bulldogs will have an allergic reaction that presents itself within the respiratory or digestive system, most reactions will come as skin problems. When exposed to an allergen, be it inhaled, eaten, contacted, or injected, the Bulldog may quickly develop round, raised, itchy spots called hives. Usually this is accompanied by swelling around the face and eyes. Atopic dermatitis is relative to hay fever in humans, however, the Bullie will respondby licking, itching, and showing small bumps and/or reddening of the skin.
The best treatment for allergies, which Bulldogs are known for being predisposed to a number of different allergies, is to identify the cause(s) of the allergy and keep the Bulldog away from it. Veterinarians routinely perform allergy testing to help correctly identify the different substances that a dog is allergic to. Once the allergens have been identified, an injectable serum is assembled to help "desensitize" the dogs response to those allergens.