Can older dogs suddenly develop allergic reactions?


Can a dog become allergic to something after years of tolerating it?

The answer is yes. Even a dog that has been healthy for years can suddenly start itching, sneezing, or reacting to food they’ve eaten their whole life. Just like humans who develop new sensitivities as adults, dogs can experience late-onset allergies too.

How Allergies Develop

Allergies occur when the immune system misidentifies something harmless — like pollen, dust mites, or a protein in food — as a threat. This doesn’t happen overnight. Your dog must be exposed repeatedly before becoming sensitised, which is why an allergy can appear months or even years later.

While most dogs show signs between six months and three years old, many only develop allergies at five, seven, or even in their senior years.

Common Late-Onset Allergies

Food allergies often appear gradually. Dogs may suddenly react to proteins like chicken, beef, eggs, or dairy, even if they’ve eaten them all their life.
Environmental allergies — pollen, mould, dust mites, and even human dander — can also develop later on. In humid climates like Singapore, dust mites and mould are constant triggers.
Flea allergy dermatitis can arise at any age. A single flea bite can cause severe reactions in allergic dogs.

Signs to Look Out For

Allergies don’t always look dramatic. Symptoms include:

  • Excessive scratching or licking
  • Red or inflamed skin
  • Recurrent ear infections
  • Watery eyes or reverse sneezing
  • Vomiting, diarrhoea, or gas (more common in food allergies)

These signs often appear slowly and are easy to mistake for normal ageing.

Getting the Right Diagnosis

If you suspect allergies, consult your vet. Many conditions mimic allergy symptoms. Blood tests may help identify environmental triggers, but for food allergies, an elimination diet (8–12 weeks) is the most reliable method.

Treatment Options

Environmental allergies usually require long-term management — baths, antihistamines, steroids, Apoquel, or Cytopoint.
Food allergies are treated by completely avoiding the trigger ingredient.

The Good News

With proper diagnosis and management, dogs with allergies can still live comfortable, happy lives. If your dog suddenly develops symptoms, don’t panic — late-onset allergies are common, and effective treatments are available.

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