There are three main allergies in pets: flea-bite allergy, food allergy and atopic dermatitis. The flea bite is by far the commonest — in an allergic animal a single bite triggers days of intense itching. The main sign of all three is relentless scratching and licking. Food allergy is confirmed with an elimination diet; atopic dermatitis is hereditary and typically appears between 6 months and 3 years of age.
Key facts:
- Three types: flea-bite allergy, food allergy and atopic dermatitis (environmental).
- Commonest by far: the flea bite — one bite is enough in an allergic animal.
- Main sign: constant scratching, licking and biting at the skin.
- Food allergy: diagnosed with an elimination diet, not a blood test.
- Atopic dermatitis: hereditary; usually appears between 6 months and 3 years.
- Complication: constant scratching leads to secondary skin infections.
Unlike people, who sneeze and wheeze, allergic dogs and cats itch. That is the whole difference, and it is why allergies in pets are so often mistaken for a skin problem rather than an immune one.
What are the three main allergies?
Flea-bite allergic dermatitis: a reaction to proteins in flea saliva. It is the commonest allergy in dogs and cats.
Food allergy: a reaction to a protein in the diet — most often a common one the animal has eaten for years, such as beef, chicken or dairy.
Atopic dermatitis: a reaction to environmental allergens such as house dust mites or pollen. It is hereditary and lifelong.
Why does one flea matter so much?
Because in an allergic animal the reaction is to the saliva, not to the number of fleas. A single bite can set off days of furious itching, long after the flea itself has gone. This is why “but I never see any fleas on him” is not reassurance, and why rigorous, year-round flea control is the first step in investigating any itchy pet.
How is a food allergy diagnosed?
With an elimination diet, which is the only reliable method — blood and saliva “allergy tests” for food are notoriously unreliable in pets. The animal is fed a strictly limited or hydrolysed diet for several weeks, with absolutely nothing else: no treats, no scraps, no flavoured medications. If the itching resolves, the original food is reintroduced to confirm it. The diet only works if the whole household observes it, which is where most attempts fail.
What is atopic dermatitis?
An inherited tendency to react to environmental allergens — dust mites, pollens, moulds. It typically appears between six months and three years of age, it is often seasonal at first and becomes year-round, and it affects the face, ears, paws and belly. It has no cure, but it is very manageable with therapeutic shampoos, essential fatty acids, flea control and medication. We cover it in detail in our guide to atopic dermatitis.
Why do allergic pets get skin infections?
Because scratching, licking and biting break the skin barrier, and the bacteria and yeasts that live harmlessly on the skin then multiply out of control. That secondary infection itches in its own right, so the animal scratches more — a self-sustaining cycle. Breaking it usually needs treating the infection and the allergy at the same time.
Frequently asked questions
What is the commonest allergy in dogs?
Flea-bite allergic dermatitis. In an allergic dog, one bite causes days of itching.
How is a food allergy diagnosed?
With an elimination diet over several weeks, with nothing else fed at all. Blood tests for food allergy are unreliable in pets.
Can allergies be cured?
Food allergy is managed by avoiding the trigger. Atopic dermatitis has no cure, but it is very controllable.
Why does my allergic dog keep getting ear infections?
Recurrent ear infections are frequently the first visible sign of an underlying allergy.
Allergies are lifelong: repeat consultations, skin tests, special diets and medication. Petplan España (Petplan Ibérica, S.L.) reimburses 100% of the vet bill up to €3,100 a year, with a €45 excess, at any vet you choose, provided it is not a pre-existing condition. See the policy terms.
