Allergies in Dogs

In dogs, "allergies" usually refers to an abnormal immune response to substances that are otherwise harmless. The most common categories are environmental allergies (canine atopic dermatitis), flea allergy dermatitis, and food allergy. Environmental allergies are often genetically influenced and typically begin between 6 months and 3 years of age. Common triggers include pollens, dust mites, molds, and other environmental proteins. Flea allergy dermatitis happens when a dog becomes hypersensitive to flea saliva, and even a small number of bites can trigger intense itch. Food allergy is less common than many owners assume and is confirmed with a veterinarian-directed elimination and challenge diet trial rather than blood or skin testing alone.

Risk factors and flare triggers include:

• Genetic predisposition, especially in breeds such as Golden Retrievers, Labrador Retrievers, Boxers, Boston Terriers, Shih Tzus, West Highland White Terriers, Shar-Peis, Scottish Terriers, Dalmatians, Lhasa Apsos, and Wirehaired Fox Terriers
• Young adult onset for many cases of atopic dermatitis
• Exposure to fleas, even if fleas are not easily seen
• Secondary skin or ear infections with yeast or bacteria, which commonly worsen itch and inflammation
• Seasonal pollen exposure in some dogs, while others become itchy year-round
• Food ingredients in a smaller subset of dogs with allergy-related skin or gastrointestinal signs

There is no single test that definitively diagnoses most chronic allergies in dogs. Your veterinarian usually starts with a history and physical exam, then works through other causes of itching and skin disease. Because allergic skin disease looks similar to many other conditions, diagnosis is often a process of exclusion.

What to expect at the appointment:

• Questions about when the itching started, whether it is seasonal, which body areas are affected, and whether there are ear or digestive signs
• A skin and ear exam to look for redness, hair loss, self-trauma, hot spots, crusting, odor, and infection
• Tests to rule out fleas, mites, lice, ringworm, and other itchy skin disorders
• Skin cytology or ear cytology to check for yeast and bacterial overgrowth
• Sometimes bloodwork, urinalysis, thyroid testing, or biopsy if other disease is suspected or medications are being considered
• A strict elimination diet trial, followed by a challenge, if food allergy is suspected
• Intradermal or blood allergy testing in selected cases to identify allergens for immunotherapy; these tests help guide treatment but do not by themselves diagnose atopy

Most allergies in dogs cannot be cured, but they can often be managed successfully with long-term care. Treatment is tailored to the type of allergy, the severity of symptoms, and whether infections are present.

Common treatment approaches include:

• Strict flea control year-round, especially for dogs with flea allergy dermatitis
• Prescription anti-itch and anti-inflammatory medications selected by your veterinarian
• Treatment for secondary bacterial or yeast skin and ear infections when present
• Bathing with veterinarian-recommended shampoos to reduce allergens on the skin and help control microbial overgrowth
• Allergen avoidance when a trigger can be identified, though this is often only partly possible
• Allergen-specific immunotherapy for environmental allergies, using testing results to create a personalized allergy vaccine; improvement may take months and is often part of long-term management
• A veterinarian-supervised elimination diet followed by challenge testing for suspected food allergy, then permanent avoidance of confirmed trigger ingredients
• Regular rechecks, because allergic disease often waxes and wanes and flare factors such as fleas, infections, and seasonal exposures need ongoing control

Call your vet sooner rather than later if your dog is miserable, develops skin sores, smells bad from skin or ears, or is not improving with the current plan.