Diagnosing Skin Allergies in Dogs

Source: PetWave, Updated on July 16, 2015
Skin Allergies

Initial Evaluation

The initial veterinary evaluation of any dog with a history of mild to intense skin itchiness, scratching and hair loss will be the same. The vet will take a complete oral history from the dog’s owner, focusing on:

  • Whether the dog has a recent history of traveling to places other than where it lives now; any recent moves?
  • When the dog’s symptoms first appeared
  • Whether those symptoms have stayed about the same, increased or decreased over time, including whether they wax and wane
  • What the dog eats and whether there have been any recent dietary changes
  • Whether the dog has access to indoor or outdoor food or other waste products, wastebaskets, trash cans, etc.
  • Whether the dog lives with or is exposed to other animals in its immediate household or environment
  • Whether the dog has a history of fleas or other external or internal parasites
  • Whether any household or landscaping chemical products have been recently introduced, including fertilizers, changes in laundry detergent and the like
  • Whether the dog has had any changes in behavior or demeanor

The veterinarian will conduct a thorough physical examination of the itchy dog. She will pay particular attention to its skin, looking carefully for any evidence of fleas, ticks or other skin-dwelling bugs. She will assess areas of redness, rashes, sores and/or hair loss. She will look closely at the dog’s eyes and ears, and also between the toes and at the tail base, for signs of irritation or infection.

Diagnostic Procedures

Allergies that cause adverse skin reactions are almost always diagnosed based on the dog’s history, physical examination and the results of tests conducted to rule out other potential causes of its symptoms. Most veterinarians will perform a fairly detailed dermatological (skin) evaluation in itchy dogs. This includes taking deep scrapings from obviously affected skin areas to look for evidence of Demodex mites, which can cause a condition called demodectic mange. Plucked hairs can be looked at under a microscope to see whether any other ectoparasites or fungal organisms are present. The veterinarian may take samples from the dog’s eyes and ears if they seem to be affected, such as when they are weeping, oozing, crusty or showing abnormal redness. Those samples will be examined microscopically to look for yeast, bacteria and other infectious organisms. Samples can be sent to a laboratory for more in depth analysis. Cultures can also be performed.

Allergy testing, similar to that done in people, is available for companion dogs at specialized veterinary clinics. However, these tests typically won’t help the veterinary team definitively diagnose the cause of a dog’s symptoms. They can help confirm or rule out immunological sensitization to the substances tested, but this may not have any bearing on the dog’s actual symptoms. Allergy testing can be performed on skin (intradermal test) or blood (serological test). Vaccinations and cross-reactions with other allergens can cause false positive allergy test results, reducing their credibility. All test results should be evaluated in light of the dog’s history, physical examination and presenting clinical signs.

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