You recognize your dog’s excessive scratching, licking and chewing at his or her skin for what they are — signs of allergies. But do you know what’s actually causing your pet’s allergies?
Your veterinarian can narrow down which allergens — the otherwise harmless substances (e.g., pollen, mold, dust or food protein) that cause the immune system to overreact — are triggering your dog’s signs and symptoms. Finding the answer will require your help, diagnostic testing and possibly time.
Diagnosis starts with a thorough history and physical exam
Figuring out which allergy or combination of allergies is causing your dog’s skin problems can be challenging for you and your veterinarian. Because itchy skin can be caused by conditions other than allergies, your veterinarian will want to rule out causes such as parasites, bacterial or fungal infections, and systemic diseases.
The process starts with a detailed history, including your dog’s breed, age, gender and reproductive status. When you seek veterinary care for your dog’s skin issue, you can help your veterinarian diagnose the underlying cause by being prepared to provide answers to a number of questions.
- When did you first notice the clinical signs and symptoms?
- How did the problem start? How has it changed?
- How old was your dog when the symptoms started?
- Where on your dog’s body did you first notice the symptoms?
- Has your dog had skin or ear conditions before?
- What treatments or medications have been used before? How did your dog to respond to them?
- Is your dog itchy?
- Which came first: the changes in skin and hair or the itching?
- Does the problem occur year-round, or does it occur only during certain seasons?
- Are there other pets in the home with similar signs?
- Are any people in your home having skin problems?
- How often do you bathe your dog? When was the last bath? What do you use for shampoo or conditioner?
- What do you use for controlling fleas, ticks or mites? When was it last applied?
- Is your dog having any other issues (e.g., increased thirst or urination, change in appetite or activity level)?
Your veterinarian will then perform a full physical examination, looking for clues as to the cause of your dog’s skin issues. Based on the history and physical exam findings, your veterinarian may request a number of laboratory tests.
These tests may include looking at skin scrapings and hair samples under the microscope and cultures of hair or skin samples to rule out fungal, yeast or bacterial infections. Blood and urine tests may be used to determine if a systemic disease is present. Combing for fleas, skin examination for fleas and flea “dirt” (feces), and skin scrapings for mites and lice also may be performed.
Diagnosing flea allergy dermatitis
Flea allergy dermatitis (FAD) is the most common cause of allergic skin diseases in dogs and a common cause of itching in dogs. That’s why veterinarians typically start with diagnostics to determine the presence of fleas and/or flea dirt when investigating skin problems in dogs. Your veterinarian will use the information you provide, such as when signs started, their duration and seasonality, and known or suspected exposure to fleas, in combination with physical exam findings.
During the exam, your veterinarian may or may not find fleas, or may only find flea dirt on your dog’s skin. Intense itching and hair loss in the area from the middle of the back to the base of the tail and down the rear legs is often seen with FAD. Skin damage or open, oozing sores may also be present.
Intradermal allergy tests similar to those performed in people or specialized blood tests can confirm flea allergy in your dog. However, the diagnosis is best confirmed by using strict flea control measures and seeing a positive response to flea control.
Diagnosing food allergy
The ideal test to diagnose or rule out food allergy is a strict food elimination diet trial that lasts eight to 10 weeks. Intradermal and serum allergy tests are available to help diagnose food allergies in dogs, but many veterinary nutritionists question the tests’ accuracy.
A detailed diet history is needed so your veterinarian can recommend an appropriate elimination diet, which is a food with either a novel protein and carbohydrate or a hydrolyzed protein. This could be home-cooked or therapeutic dog foods. An elimination diet trial also means no treats, no table food, no rawhides, no flavored chews or toothpaste, and no flavored medications.
If no improvement is seen by the end of the trial — and the trial was strictly performed — food allergy can be ruled out. Your dog can be transitioned back to his or her normal diet and other causes of skin allergies can be followed.
If your dog improves on the elimination diet, the next step is to challenge your dog by feeding the previous food and watching for clinical signs to recur. While this step verifies that the improvement was related to food and not a new medication or shampoo, many owners are often unwilling to try it.
Diagnosing atopic dermatitis
No specific diagnostic test exists for atopic dermatitis, or environmental allergies. Instead, veterinarians arrive at a diagnosis of atopy by ruling out other causes of itchy skin conditions, the presence of clinical signs and the information in your dog’s history. Among the factors that your veterinarian uses to make a diagnosis are:
- The dog’s age when the skin condition started
- The level of itchiness, or pruritus, which is often present before other signs occur
- The areas on your dog’s body that are affected, such as the feet, face, “armpits,” neck, abdomen and inguinal region
- Changes in or progression of clinical signs
- Seasonal or year-round signs and symptoms
After diagnosis, intradermal or serum allergy tests are used to identify the specific environmental allergens so they can be avoided — which is often impractical — or used for therapeutic immunotherapy. Immunotherapy, commonly referred to as “allergy shots,” is designed to improve your dog’s tolerance of specific allergens. Intradermal and serum allergy tests aren’t used to diagnose atopic dermatitis and may not be done unless you’re will to try immunotherapy.
Once your veterinarian has determined the underlying cause of your dog’s itchy skin, a treatment plan that’s right for your dog can be formulated. Since allergies can’t be cured, only managed, the goal will be to make your dog more comfortable and control allergy signs and symptoms.
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