5 Things That May Trigger Your Pet’s Allergies  

Medically reviewed by Dr. Harinder Babbar, DVM
Veterinarian & Medical Director, McQueen Animal Hospital, Brampton, Ontario

This article has been medically reviewed and is based on current evidence-based veterinary literature and clinical guidance.

The five common allergy triggers in dogs and cats are flea bites, pollen, house dust mites, mould spores and certain food ingredients. These allergens can cause itchy skin, paw licking, excessive grooming, hair loss and recurring ear problems. Some allergies flare up seasonally, while others affect pets throughout the year.

However, similar symptoms can also occur with parasites, infections and other skin conditions. Identifying the trigger is important because changing your pet’s food or treating the itching alone may not resolve the underlying problem.

What Are the Common Signs of Allergies in Dogs and Cats?

Allergies often affect a pet’s skin, but dogs and cats may show discomfort differently.

Common allergy symptoms in dogs include:

• Frequent scratching, particularly around the ears, belly and armpits
• Repeated paw licking or chewing
• Red, inflamed or irritated skin
• Hair loss from persistent scratching
• Recurring ear inflammation or infections
• Rubbing the face against furniture or carpets

Common allergy symptoms in cats include:

• Excessive licking or grooming
• Bald patches around the belly, legs or sides
• Small scabs or crusty bumps on the skin
• Frequent scratching around the head and neck
• Inflamed skin or recurring ear problems

Not every itchy pet has an allergy. Fleas, mites, bacterial infections and fungal conditions can produce similar symptoms.

If your dog is scratching constantly, read our guide on why dogs itch and when you should worry to understand other possible causes.

5 Common Allergy Triggers in Dogs and Cats

1. Flea Bites Can Cause Severe Skin Allergies

Flea bites are a major cause of allergic skin problems in dogs and cats. Some pets develop flea allergy dermatitis, an allergic reaction to proteins in flea saliva.

For a sensitive pet, even one or a few flea bites may cause intense itching.

In dogs, the irritation commonly appears around the lower back, base of the tail and hind legs. You might notice your dog chewing these areas or developing red patches, scabs and hair loss.

Cats can show different symptoms. Some develop small crusty bumps along their back and neck, while others groom excessively until bald patches appear.

Can indoor pets get flea allergies?

Yes. Indoor dogs and cats can still be exposed to fleas brought into the home by other animals or from contaminated environments.

You may not see fleas on your pet, especially if your cat frequently grooms its coat.

How to reduce the risk:

• Use veterinarian-recommended flea prevention suitable for your pet.
• Check all pets in the household for possible flea exposure.
• Wash pet bedding and vacuum sleeping areas regularly.
• Ask your veterinarian about treating the home if an infestation is present.

Avoid using dog flea treatments on cats unless the product is specifically approved for cats. Some dog flea products contain ingredients that are highly toxic to felines.

2. Grass, Tree and Weed Pollen Can Trigger Seasonal Allergies

Does your dog start licking its paws every spring or summer? Does your cat scratch more frequently during certain months?

Pollen from grasses, trees and weeds is a recognised environmental allergy trigger.

Unlike people, who frequently experience sneezing or watery eyes from seasonal allergies, allergic dogs often develop itchy skin.

You may notice your dog:

• Licking its paws after spending time outdoors
• Scratching around the ears or face
• Developing redness between its toes
• Rubbing its body against furniture

Cats affected by environmental allergens may scratch around their head or neck or groom excessively.

Pollen exposure changes throughout the year, which is why some pets experience recurring symptoms during particular seasons.

How to reduce pollen exposure:

Gently wipe your dog’s paws after outdoor walks. Wash bedding regularly, and consider keeping windows closed during periods of heavy pollen exposure.

You can also record when the symptoms occur. If your pet becomes itchy around the same time every year, that information may help your veterinarian investigate a possible environmental allergy.

These measures may reduce exposure, although they cannot completely prevent contact with airborne pollen.

3. House Dust Mites Can Cause Year-Round Allergies

If your pet scratches throughout the year, allergens inside your home may be contributing to the problem.

House dust mites are microscopic organisms found in household dust, carpets, mattresses, bedding and upholstered furniture.

Some dogs and cats develop allergic skin reactions to dust mite allergens.

Because dust mites are present indoors, symptoms may continue even when pollen levels are low.

Common signs can include:

• Persistent itching without a clear seasonal pattern
• Paw licking or face rubbing
• Skin redness or irritation
• Excessive grooming in cats
• Repeated ear problems

These signs do not confirm a dust mite allergy on their own.

How to reduce dust mite exposure:

Wash your pet’s bedding regularly, vacuum carpets and furniture, and keep sleeping areas clean.

If your pet sleeps on upholstered furniture or your bed, consider how frequently those areas are cleaned.

Regular cleaning may reduce allergen exposure, but it won’t necessarily resolve an established allergy.

If your pet continues scratching despite changes at home, arrange a veterinary examination rather than assuming that dust mites are the cause.

4. Mould Spores Can Contribute to Environmental Allergies

Mould is another potential allergy trigger for dogs and cats, especially in damp indoor environments.

Mould spores can be found around water-damaged areas, poorly ventilated rooms, damp basements and decaying outdoor vegetation.

In susceptible pets, exposure may contribute to allergic skin inflammation.

The symptoms can resemble other environmental allergies, including itching, paw licking and skin irritation.

Mould exposure does not automatically explain a pet’s skin problem. A proper veterinary assessment is needed to rule out other possible causes.

How to reduce exposure:

• Check areas where your pet sleeps for moisture or visible mould.
• Fix water leaks and address persistent dampness.
• Improve ventilation where appropriate.
• Keep bedding dry and clean.
• Prevent pets from entering areas undergoing mould removal or chemical cleaning.

Avoid spraying strong cleaners or disinfectants around your pet without checking their safety.

If skin irritation continues after environmental improvements, ask your veterinarian whether further investigation is necessary.

5. Certain Food Ingredients Can Trigger Allergic Reactions

Food allergies can affect both dogs and cats, although not every pet with itchy skin has a food allergy.

Some animals develop reactions to particular dietary proteins, including ingredients such as beef, chicken, dairy, fish or eggs.

A pet may develop a food allergy even after eating the same food for months or years.

Unlike some pollen-related allergies, food allergy symptoms often occur throughout the year.

Possible signs include:

• Persistent, nonseasonal itching
• Recurring ear or skin inflammation
• Paw licking or excessive grooming
• Hair loss caused by scratching
• Digestive symptoms such as vomiting or diarrhoea in some pets

Should you change your pet’s food immediately?

Not necessarily.

Switching repeatedly between commercial pet foods may make it more difficult to identify a genuine food allergy. A food allergy cannot be confirmed simply because symptoms improve after changing brands.

Veterinarians typically use a carefully controlled elimination diet followed by a dietary challenge when food allergy is suspected.

Learn how this diagnostic process works in our article on food elimination trials for pets.

For general feeding considerations unrelated to allergy diagnosis, you can also read what you should really feed your pet.

Seasonal vs Year-Round Allergies: What’s the Difference?

The timing of your pet’s symptoms can provide useful clues about possible triggers.

These patterns are only clues. Pets can react to more than one allergen, and flea exposure or environmental conditions can change throughout the year.

A pet with constant itching may have environmental allergies, food allergies, an infection or another skin disease. The timing alone cannot establish a diagnosis.

How Do Veterinarians Identify Allergy Triggers in Pets?

A veterinarian usually begins by examining your pet’s skin, ears and coat, along with reviewing their medical history.

You may be asked:

• When did the scratching first begin?
• Does it happen throughout the year or during particular seasons?
• Is your pet taking regular flea prevention?
• Have you noticed ear infections or digestive symptoms?
• Has your pet recently changed foods, treats or environments?
• Have previous treatments improved the symptoms?

The next steps depend on what the examination reveals.

Your veterinarian may recommend skin or ear samples to check for bacterial or yeast infections, examine for parasites, or investigate other skin conditions.

McQueen Animal Hospital offers pet pathology and diagnostic services in Brampton, including examination of skin samples for certain parasites when clinically appropriate.

If food allergy remains a possibility, a controlled elimination diet may be considered.

For suspected environmental allergic skin disease, allergy testing may help select allergens for immunotherapy after the condition has been evaluated. A positive allergy test alone does not confirm the diagnosis.

The goal is to identify contributing causes before deciding on treatment.

How to Reduce Allergy Exposure at Home

You may not be able to eliminate every allergen, but a few practical habits can help reduce exposure and provide useful information for your veterinarian.

Keep flea prevention consistent. Follow a veterinarian-recommended prevention schedule and avoid using products intended for another species.

Clean your pet’s sleeping areas. Wash bedding regularly and vacuum carpets or upholstered furniture where your pet spends time.

Pay attention to outdoor symptoms. If your dog becomes itchier after walks, wipe its paws gently and record when flare-ups occur.

Address damp areas. Fix moisture problems around the home and keep bedding dry.

Avoid unnecessary diet changes. Don’t remove major food groups or start a restrictive homemade diet without veterinary advice.

Maintain a symptom record. Note when the itching starts, where your pet scratches, whether it happens seasonally and what treatments have been tried.

Most importantly, avoid giving human allergy medications or applying medicated creams without veterinary guidance.

These steps may help manage exposure, but persistent itching needs proper assessment.

When Should You Take Your Pet to a Veterinarian for Allergies?

Occasional scratching is normal. Persistent scratching, repeated ear problems or skin damage should not be ignored.

Arrange a veterinary appointment if your dog or cat:

• Scratches, licks or chews its skin repeatedly
• Develops red patches, scabs or bald areas
• Experiences frequent ear irritation or discharge
• Has an unpleasant smell from the skin or ears
• Continues itching despite appropriate flea prevention
• Develops repeated skin problems during particular seasons

Early assessment can help identify infections, parasites and other conditions that may be making your pet uncomfortable.

When is an allergic reaction an emergency?

Difficulty breathing, collapse or sudden significant facial swelling may indicate a serious reaction and require immediate veterinary attention.

If you suspect a severe reaction, seek emergency veterinary care without delay. McQueen Animal Hospital provides emergency veterinary care in Brampton during its clinic hours. Call ahead when possible. If the hospital is closed, contact an open emergency veterinary facility.

Frequently Asked Questions About Allergies in Dogs and Cats

What are the most common causes of allergies in dogs?

Flea bites, environmental allergens such as pollen and dust mites, and certain food ingredients are established allergy triggers in dogs. The cause varies between pets, and similar symptoms can also result from infections or parasites.

Can indoor cats have allergies?

Yes. Indoor cats can develop allergies associated with fleas, house dust mites, food ingredients and other environmental allergens. Indoor living does not eliminate every potential trigger.

Why is my dog itching even though it has no fleas?

Environmental allergies, food allergies, mites and skin infections are possible causes. Flea allergy also remains possible even if you cannot see fleas. A veterinary examination can help identify the problem.

How do I know if my pet has seasonal allergies?

Symptoms that repeatedly occur during particular months may suggest a seasonal environmental allergy. However, the timing alone is insufficient for diagnosis because other conditions can cause similar itching.

Can pet allergies cause recurring ear infections?

Yes. Allergic skin disease can contribute to repeated ear inflammation and secondary infections. Pets with ear redness, odour, discharge or frequent head shaking should be examined by a veterinarian.

Are food allergies more common than environmental allergies in dogs?

Generally, environmental allergies are more common than food allergies in dogs. Food allergy is still an important possibility, especially when symptoms occur year-round and other causes have been investigated.

Can pet allergies be cured permanently?

Some triggers can be avoided once identified, particularly certain dietary ingredients. Environmental allergic skin disease often requires ongoing management. Treatment depends on the underlying cause and the individual pet.

Should I give my dog or cat allergy medicine at home?

Do not give human allergy medications or use medicated creams without veterinary advice. Some medicines are unsuitable for pets, and treating the itching without identifying the cause may delay appropriate care.

Concerned About Allergies in Your Dog or Cat? Visit McQueen Animal Hospital

If your pet is constantly scratching, licking its paws or developing recurring skin irritation, the next step is to identify what’s causing the discomfort.

McQueen Animal Hospital in Brampton provides veterinary consultations and examinations for dogs and cats. Our veterinary team can assess your pet’s symptoms, discuss possible allergy triggers and recommend appropriate diagnostic and treatment options.

Book a pet consultation and examination in Brampton or call 905-455-7387 to arrange an appointment.

McQueen Animal Hospital

8975 McLaughlin Road South, Brampton, ON L6Y 0Z6, Canada

This article provides general pet health information and does not replace an individual veterinary examination.