Most pets don’t “get allergies” in a neat, obvious way. It usually starts as an itch that doesn’t settle, a dog chewing at its feet, a cat over-grooming until the coat thins, or ears that keep flaring up. Left alone, that steady irritation can turn into skin infections, sore ear canals, and a cycle of scratching that’s hard to break.
The useful question is rarely “Is it allergies?” and more often “Which kind, and what else could it be?” The signs overlap with fleas, mites, infection, and diet-related reactions. The aim is to notice patterns early, rule out the common look-alikes, and then manage what’s left with a plan that’s realistic for your household and safe for your pet.1, 2
Common symptoms of allergies in pets
In dogs and cats, allergies usually show up through the skin first. The surface story is itch, but the details matter: where it itches, how often, and what the skin and ears look like alongside it.2, 3
Skin signs (the most common pattern)
- Persistent itching (pruritus), rubbing, scratching, chewing, or over-grooming.2, 3
- Redness, rashes, hair loss, thickened or crusty skin, “hot spots”, or a change in coat quality from constant licking and inflammation.2
- Paws, face, belly, armpits, groin, and ears are common trouble spots in dogs with allergic skin disease.2, 3
Ear problems that keep coming back
Itchy ears, head shaking, and recurrent ear infections are a very common companion to allergic skin disease in dogs. If the ears keep flaring even after treatment, it’s a strong hint that something underlying (often allergy) is driving the irritation.2, 3
Respiratory signs: possible, but less common in pets than in people
Sneezing and runny eyes can happen, especially with environmental triggers, but many pets with allergies mainly show skin and ear signs rather than “hay fever”-style symptoms.3
Gut signs (more suggestive of diet-related reactions)
Some pets with adverse food reactions have vomiting or diarrhoea, but skin signs (itch and inflammation) are still common. Because many different conditions can cause digestive upsets, it’s worth treating vomiting/diarrhoea as its own clue rather than assuming “food allergy” straight away.5
What causes pet allergies?
“Allergies” is a bucket term. In practice, vets usually think in a few overlapping groups: flea allergy dermatitis, environmental allergy (often called atopic dermatitis), and adverse reactions to food. More than one can be present at the same time.2, 6
Fleas: the small bite that can cause a big itch
Some pets are allergic to flea saliva. In those animals, a single bite can trigger intense itching, even if you never see a flea. This is one reason vets often insist on strict, year-round flea control when working up chronic itch.2
Environmental allergens (atopic dermatitis)
Pollens, grasses, mould spores, and dust mites are common environmental triggers. Signs may be seasonal or year-round depending on the allergen and where you live.2, 6
Food-related reactions
Food allergy (more broadly, cutaneous adverse food reaction) is usually driven by proteins in the diet and can develop over time, even if the food has been tolerated for years. It can look very similar to environmental allergy on the skin, which is why diagnosis relies on a proper diet trial rather than guesswork.2, 5
Genetics and breed
Some pets are genetically predisposed to allergic skin disease. Breed risk varies by region and breeding lines, so it’s more useful to treat breed as a “higher suspicion” flag than a diagnosis.6
How vets diagnose pet allergies (and why it can take time)
There isn’t one perfect screening test that proves a pet “has allergies”. Diagnosis usually starts with the basics: history, where the itch is, what the skin and ears look like, and then systematically ruling out the common mimics—parasites and infections first, then diet-related reactions if needed.6, 7
Ruling out the look-alikes
Allergic pets often pick up secondary bacterial or yeast infections because damaged skin becomes an easy place for microbes to overgrow. Treating infection without addressing the driver can give temporary relief, then the cycle returns.6, 7
Allergy testing has a specific role
Intradermal skin testing and blood (IgE) tests don’t answer “Does my pet have atopic dermatitis?” They are mainly used after a clinical diagnosis is made, to help choose allergens for allergen-specific immunotherapy (desensitisation).7, 8
Managing and treating pet allergies
Allergic skin disease is usually managed rather than cured. The aim is quieter skin: less itch, fewer flare-ups, and fewer ear infections. Treatment is often layered—flea control, skin care, and medication as needed—with the intensity matched to how bad the signs are and how often they return.6
Step 1: Control fleas and treat infections
Even if fleas aren’t obvious, consistent flea prevention is often non-negotiable in itchy pets. If there’s yeast or bacterial infection, it needs targeted treatment, otherwise the itch remains loud no matter what else you do.2, 6
Step 2: Reduce “allergen load” on the skin
Bathing can help some itchy dogs by washing pollen and other allergens off the coat and soothing inflamed skin. The right frequency and product depends on the pet and the state of the skin, so it’s best guided by your vet—especially if the skin is broken or infected.6
Step 3: Medicines to relieve itch and inflammation
Your vet may recommend different options depending on species, severity, and other health issues. For dogs with atopic dermatitis, commonly used approaches include:
- Antihistamines (often mild benefit, more useful in some dogs as part of a broader plan).6
- Corticosteroids (effective, particularly for flares, but side effects limit long-term use).6
- Oclacitinib (a JAK inhibitor) or lokivetmab (a monoclonal antibody) for itch control in dogs, depending on the case.6
- Cyclosporine for longer-term control in some dogs (slower onset than “flare” medications).6
Allergen-specific immunotherapy (desensitisation)
For some dogs with atopic dermatitis, allergen-specific immunotherapy (ASIT) can reduce signs over time. It’s slow-acting—often months before clear improvement—and it’s usually built from allergy testing results once other causes of itch have been ruled out.6, 8
Diet trials (for suspected adverse food reaction)
If food is suspected, the usual approach is a strict elimination diet trial prescribed by your vet, followed by a controlled re-challenge. This is fiddly, but it’s the most reliable way to separate food-related itch from environmental allergy.2
Prevention and day-to-day habits that help
There’s no single household trick that “stops allergies”, but small, steady steps can take the edge off flare-ups and reduce how often medication is needed.
At home
- Keep flea prevention consistent (ask your vet what “consistent” means for your area and pet’s lifestyle).2
- Wash bedding regularly, especially if your pet has recurring skin infections or flare-ups.2
- After grass or high-pollen outings, a quick rinse or wipe-down of paws and belly can reduce what’s carried into the house and onto the skin.4
Grooming
Regular brushing helps remove allergens and keeps you close to the skin, where early redness or scabbing can be missed under fur. If bathing is part of your plan, aim for products and frequency recommended for allergic or sensitive skin—too much washing can dry the coat and worsen irritation.6
When to seek professional help (and when it’s an emergency)
Book a vet visit if the itch lasts more than a few days, keeps returning, or you notice ear trouble, hair loss, broken skin, or a smell that suggests infection. Chronic itch is rarely “just cosmetic”; it’s a medical problem with predictable complications if it’s left to run.2, 3
Go to an emergency vet now
Severe allergic reactions (anaphylaxis) are uncommon, but they are time-critical. Treat these signs as an emergency:
- Difficulty breathing or marked respiratory distress.9, 10
- Collapse, extreme weakness, or signs of shock (pale gums, confusion).10
- Sudden facial swelling, widespread hives, or severe whole-body itch—especially if paired with vomiting/diarrhoea.9, 10
Final thoughts
Allergies in pets are often a long, quiet pattern rather than a single dramatic event: itchy feet, irritated ears, and skin that never quite settles. The most effective care is usually plain and methodical—control fleas, treat infections properly, test diet only when it’s justified, and choose longer-term medications or immunotherapy when the itch keeps returning.2, 6
References
- RSPCA Pet Insurance (Australia) — Common cat and dog skin conditions
- RSPCA NSW — Seasonal allergies in pets
- RSPCA Victoria — Common health conditions explained (skin problems, ear infections)
- Merck Veterinary Manual — Canine atopic dermatitis (professional version)
- FOUR PAWS Australia — Food allergies in pets
- Merck Veterinary Manual — Select therapeutic agents for atopic dermatitis (table)
- dvm360 — Canine allergic dermatitis: clinical signs and diagnosis (role of allergy testing)
- Dermcare (Australia) — Allergen-specific immunotherapy (ASIT) for canine atopic dermatitis
- VCA Animal Hospitals — Anaphylaxis in dogs
- PLOS/PMC — Basic triage in dogs and cats: anaphylaxis clinical signs
Veterinary Advisor, Veterinarian London Area, United Kingdom