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Can Dogs Suddenly Develop Allergies?

Written by Anna Hollisey


happy aussie puppy rolling on the grass

Short answer: yes, they can! In this article, we dig into the science to learn how and why our dogs develop allergies at different stages of life. 

Does Your Dog Have Allergy Symptoms?

An allergy is not easy to diagnose. That’s because almost all allergy symptoms can be linked to other conditions and diseases, and some can even be serious.

*If your dog’s behavior has changed, or they’ve suddenly developed any of these symptoms, it’s important to get them checked by a vet. They’ll carry out the right tests to rule out severe conditions.*

However, it’s important to know that dogs can develop new allergies at any age. That means it’s helpful to be vigilant and watch for the key indicators. These are the main allergy symptoms in dogs:

  • Itchy skin/learn/dog-health/dog-itching-remedies (all over, or mainly the paws, particularly for dogs with a food intolerance)
  • Swollen facial features or ears (caused by excessive histamine production)
  • Runny nose and sneezing
  • Diarrhea, vomiting and lethargy (often related to food intolerance)
  • Anaphylactic shock (rare but dangerous – with increased heart rate and difficulty breathing). 

Most Common Allergies in Dogs

An allergy is caused when the immune system overreacts to an allergen. It can be inherited or prompted by years of exposure. Dog allergies are quite common, especially the environmental types. Allergies tend to be grouped in three main categories:

Environmental Allergies. 

Human allergens – like dust mites, mold, and all kinds of pollen – can affect dogs too. These are often seasonal (which helps us to identify the specific allergen affecting our dog!).

Can an environmental allergy develop suddenly? This type of allergy is more likely to be inherited (and will generally show by the time your dog is 3 years old). But symptoms can worsen over time, or if you move home, so your dog may appear to have developed a new allergy. 

Flea Allergy. 

If your dog has Flea Allergy Dermatitis (FAD), just one flea bite could drive them to distraction. Fleas inject saliva when they latch on to a dog’s skin. This contains irritating antigens, which makes the dog itchy. Dogs can also be allergic to other insect bites, such as spider or bee bites. 

Can flea allergies develop suddenly? FAD can start at any time in your dog’s life. If they have other allergies, they’re more prone to developing FAD. 

Food Allergies.

Food intolerance isn’t strictly an allergy, but it involves a biological reaction to a trigger food. The most common food ‘allergies’ in dogs are beef, chicken, dairy, soy, and eggs. Dog food which is labeled ‘hypoallergenic’ will not usually contain any of these ingredients. 

Can food allergies develop suddenly? Yes. But the sudden onset of symptoms isn’t as sudden as it appears. Your dog has been building up an immune response to the allergen, and now the antibodies have reached an excessively high level. In effect, your dog’s body is trying to repel the allergen, which eventually causes symptoms such as stomach pain, diarrhea and vomiting.

Treating Dog Allergies

First, make an appointment with your vet. (We know… nobody likes it, especially the dog.) It’s important to get an expert opinion in case the symptoms are caused by something completely different. The vet may recommend tests:

  • Food trial. Switch to a hypoallergenic dog food and make sure that the entire household is strict about feeding (no table scraps!). Give it 12 weeks to see whether the new diet is helping your dog. 
  • Blood tests. Optional RAST tests can be used to identify environmental allergens – ask your vet to explain the process of hypersensitization.
  • Skin tests. Prescribed for dogs with dermatitis, this can rule out other conditions. 

Once your dog is diagnosed, you’ll have several treatment options: