Allergies in dogs often start with a scratch. Allergies are one of the top reasons for canine vet visits, especially during the spring and summer months. They can begin at any age, most commonly between 1 and 3—but may appear as early as 6 months. What Is an Allergy? An allergy is a state of overreactivity or hypersensitivity to an allergen. An allergen can be anything that triggers an allergic reaction, and the list is endless. Allergies are most commonly categorized as eith