Finding the root of the allergy


Brush up your knowledge on allergic disease for the itchy dog

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“How common is allergic disease?” Julia E. Miller, DVM, DACVD, asked attendees at the Fetch conference in Charlotte, North Carolina.1 The answer: fairly common, when comparing to all other reasons pets come into the veterinary clinic.

Miller, an assistant clinical professor of dermatology at Cornell University College of Veterinary Medicine in Ithaca, New York, shared evidence of this commonality with data conducted by Healthypaws insurance in 2017-2018. The data found 39% of veterinary clinic cases were dermatology related, and specifically allergies. This 39% was comprised of 17% to 22% skin conditions, 12% ear infections, and 5% other allergies.1,2 Miller also shared with attendees that the word “atopy” comes from the Greek word “atopia” which means uncommonness. This is ironic with how common it is for veterinary medicine.

Allergic dermatitis occurs the pet’s skin develops an allergic reaction, but veterinary professionals need to identify what is causing the dermatologic condition, before diagnosing it properly. To start, a thorough history for each patient should be taken, and it should include the following components:

  • Breed
  • Age at onset
    • Atopy is typically seen at ages 1-4 years, however there are exceptions in French bulldogs, bully breeds, German shepherds, Wheatons, and more.
    • Food allergy can come at any age.
      • 38% of dogs develop a food allergy at less than 6 months of age.
  • What season was it at onset? (This can point to an environmental allergy vs a food one)
  • Did the rash or itch come first?
  • Is the dog taking a flea preventive? What is it? How often is it applied? What is the proper application technique?
  • Are there any gastrointestinal signs present? (This may point towards a food allergy)
  • What diet is the pet on currently?


Atopy cases are more common for an allergic disease, affecting 10% to 15% of dogs. Some common signs include scratching behind the elbows, licking and chewing the feet, rubbing at the face, and scooting. Excessive scratching and licking may also contribute to hair loss.3

Food allergy

According to Miller, 10% to 25% of atopy dermatitis cases are caused by a food allergy. Food allergy, more formally referred to as cutaneous adverse food reaction, is an adverse immunologic reaction to an allergen in the diet. Food allergy is commonly a protein such as chicken, beef, lamb, or fish, however, any carbohydrate or fat may also be an allergen. Diagnosing a food allergy can be quite frustrating since it presents very similarly to environmentally-caused allergies. The same signs of scratching, licking, and scooting can be present. To get an accurate diagnosis, there needs to be a strict, prescription diet trial.

Over the counter diets are not a prescription diet trial but can be called a diet change. Home-cooked is the best practice with strict guidelines from your veterinary dermatologist.

According to Miller, after 3 weeks on a diet trial, more than 50% of dogs will show improvement. After 5 weeks, more than 85% of dogs show improvement, and after 8 weeks, this jumps up to more than 95% of dogs showing improvement. Miller stated, “So the way that I feed diets is I have the client check back in with me at 4 to 6 weeks. If there is zero change in 4 to 6 weeks, I am done. I do not feed that diet for another 2 months. If there is some change in that 4-to-6-week plan, I continue the diet a little bit longer and see how good I can get it.”

However, Miller cautioned attendees to not bother with the diet trial if the client is unwilling or cannot do it right. She emphasized that diet trials are tough because of how strict they are and how consistent clients need to be with them. “If a client is unwilling or unable to do it at trial, just don't do it,” she said.


  1. Miller JE. The itchy and scratchy show: How to confidently diagnose canine allergies (part 1). Presented at: Fetch dvm360 conference; Charlotte, North Carolina; March 15-17, 2024.
  2. Common dog and cat illnesses and accidents. Healthypaws Pet Insurance and Foundation. 2017-2018. Accessed March 15, 2024.
  3. Collins B. Atopic dermatitis (atopy). Cornell University College of Veterinary Medicine. Accessed March 15, 2024.
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