Pet Allergies

If you’ve ever asked yourself, “How do I know what my dog is allergic to?”—this blog post is for you. Our resident Veterinary Dermatologist Dr. Anthea Schick helps decode three types of allergies and what to look for.  

Skin and ear problems are common in dogs, and they’re one of the most frequent reasons that owners bring their pets to the veterinarian. While there are many different reasons why a pet will lick, rub, scratch, and chew, the most common is allergies. Allergies are defined as a chronic condition involving an abnormal reaction to an ordinarily harmless substance called an allergen. Allergens can trigger a response that starts in the immune system and results in an allergic reaction. 

When dogs are allergic, instead of sneezing and hay fever, they mostly show their allergies in their skin and ears. Allergic dogs are basically like people with eczema. But in order to better understand what your dog is suffering from, it helps to break down some allergy basics.



Environmental Allergy: Just like people, dogs (and cats) can be allergic to pollen, dust, and molds. Allergic dogs may scratch all over—especially at their armpits, belly, ears, and paws. They may also have recurrent skin and ear infections and lick their paws. The signs usually start between 6 months to 5 years of age. Also take note if this reaction happens during a particular season, like Spring or Fall. 

Food Allergy: Animals with a food allergy can show very similar signs as pets with environmental allergies, but the itching is not seasonal. Animals can develop a food allergy at any time in their life—even if they have been eating the same food all along. In fact, one of the most common food allergens is chicken. Besides itchiness, food-allergic dogs may also have ear or skin infections. The symptoms of a food allergy usually do not improve much with anti-itch medications. 

Parasite Allergy: Fleas cause itching and hair loss due to the irritation caused by their bites, secondary bacterial infections, or to a flea bite allergy. Animals will often itch and lose hair on their back near their tail. In flea-allergic animals, even one flea bite can cause a reaction. Mange mites (sarcoptes or scabies mites) can also cause intense allergic reactions and extreme itch. Scabies may cause hair loss and crusts to form on ears and elbows. Scabies mites can be very difficult to find, and, if suspected, should be treated even if skin samples don’t reveal mites. 



If you can’t easily figure out what type of allergy your dog has, there are things you can do to help pinpoint the problem. 

Some parasites, like fleas and ticks, are usually easy to find since they are visible to the naked eye. Other skin parasites can be tricky to find. Demodex mites live inside hair follicles and can usually be found by veterinarians with skin scrapings. Skin scraping involves using a dull blade or medical skin spatula to scratch the skin to acquire samples of skin cells and any parasites that may be present. Scabies (sarcoptes) mites can be very hard to find and might be present even if skin scrapings are negative. There are several other types of parasites, like Cheyletiella (also called walking dandruff) and a variety of species of lice, that you’ll also need help from your vet to detect. Luckily, there are newer prescription parasite medications that treat them all!

Unfortunately, no easy test exists that will give you all the answers about your dog’s allergies. Blood or skin testing for food allergies is not usually accurate in dogs and cats. And while an internet search will reveal that many companies claim they’ll give you answers about your pet’s food allergy, most of them have been shown to be highly inaccurate and some have even been shown to be scams

Since you can’t rely on food allergy testing, the only way to determine if your dog has food allergies is to talk to your vet about performing a diagnostic diet trial for 8-12 weeks. Prescription hydrolyzed protein diets are the most reliable diets since the proteins in them have been broken down into small pieces that the immune system can’t recognize. They have also been tested for impurities. (Switching to another commercial diet usually does not help, because most of these diets have similar ingredients and many have been found to have trace amounts of ingredients that aren’t listed on the label.) During the test diet, all other food, including treats, supplements and chews, must be stopped.

Once food allergies and parasites have been eliminated, accurate testing does exist for environmental allergens. 

Blood allergy testing is more convenient and can be performed by most veterinarians, but may be less accurate than skin testing. Skin allergy testing tests the actual organ that is involved in the allergy (the skin), so is more accurate than blood testing, and is typically performed by veterinary dermatologists. Once the allergy test results are known, allergic pets can receive allergy shots (just like people!) to desensitize them. 



Although the main reason for a pet’s itchy skin may be allergies or parasites, they can also often get secondary bacterial or yeast infections which can keep the itch going even if the underlying cause is treated. These infections can cause red, crusty, flaky skin as well as hair loss, pimples, and red bumps. Chronic allergies with secondary bacterial or yeast infections can cause skin to look thickened and “elephant-like.” If an irritation persists, consult your family vet or seek the help of a board-certified veterinary dermatologist.

While we never recommend self-diagnosing your Best Dog Friend, we hope this information helps you better understand how you can speak up for your pup and spare them from some chronic scratching.

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