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Signs of Allergies in Dogs: Types and What to Look For



Dogs and people share many traits, among them having allergies and allergic reactions. But not all allergies show up the same way. At first glance, you might not know if your dog has seasonal allergies, food allergies, or something else.

Understanding the signs of allergies in dogs can help reveal possible solutions, including whether to reach for over-the-counter medications or consult your veterinarian. It is always important to rule out other underlying conditions, such as skin parasites, before treating a dog for allergies. 

Canine allergies can range from mild discomfort to life-threatening, so the sooner a dog gets a diagnosis and treatment, the sooner they can feel better.

‌What is an allergy?

‌An allergy starts with an allergen—typically a foreign substance or food component—that doesn’t usually bother the canine body. A dog’s immune system creates immunoglobulin E (IgE) antibodies in defense, reacting to this allergen by releasing chemicals like histamines to stop it from spreading further.

Why dogs get allergies

‌Allergies are multifactorial and have multiple causes, and some canine allergies have external and internal (i.e., genetic) connections. While some allergies come from a naturally bothersome source, others are due to certain genetic differences that inappropriately ramp up the immune response of  individual dogs or entire breeds.

Allergic disease can run in families, and they can run in breeds as well, making genetic history important for breeding decisions and individual medical history. Genetic testing, like dog DNA tests from Embark, can help identify breed traits and genetic health risks. These tests can also help worried dog lovers understand why their dog is dealing with allergic disease.

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Which allergies are most common in dogs?

‌In dogs, allergies come in three primary forms: flea, environmental (sometimes called atopy), and food.

Flea allergies are the most common canine allergy and can happen anywhere there are flea populations. They can also occur any time of year. As little as one flea bite can trigger this response.

Environmental allergies can be seasonal and peak at specific times of year, especially spring and summer. Exposure to these allergens occurs via skin contact or inhalation. Environmental allergies can also be due to indoor and non-seasonal substances such as dust mites, molds, and many others. Less common are contact skin allergies. These allergies can be due to ingredients in medication, hygiene products, fabrics, or something else. Skin redness and irritation are the most likely signs a dog would show to a contact allergy. 

Food allergies, on the other hand, come from the body having an abnormal response to any food component. These allergies can occur in up to 2% of dogs.

Types of canine allergies

Flea allergies for dogs

‌Insects, including fleas, can cause dermatitis with severe itching. For some dogs, though, flea bites can lead to canine flea allergy dermatitis (FAD). FAD in dogs is due to hypersensitivity to substances in flea saliva, and it can cause severe skin reactions long after the flea has jumped off.

Flea allergy dermatitis is the name of the skin irritation that occurs in response to a flea bite allergy in allergic dogs.  Spotting fleas or flea dirt helps with the diagnosis, but sometimes, a dog can develop signs of flea allergy dermatitis from one brief flea bite. Recent history of dog parks, boarding, grooming, or interaction with other animals could make flea exposure more likely. 

Environmental allergies for dogs

Environmental allergies can be difficult to determine, but sometimes it helps to pay attention to whether they are seasonal or year-round. Like people, dogs have mast cells in their skin that store histamines for a quick immune response to an allergen. Although some dogs react to seasonal allergens with a runny nose or sneezing, they are much more likely to get itchy skin. 

Environmental allergies in dogs can happen from a variety of indoor and outdoor allergens. Some of them include:

  • Insect bites
  • Tree pollen
  • Grass pollen
  • Flower and weed pollen
  • Dust and dust mites
  • Mold spores
  • Mildew

It has been estimated that 10 to 15% of dogs are affected by atopic dermatitis due to a reaction to an allergen in the environment. 

Atopic dermatitis is a disease with genetic and environmental influences. In more recent research, it has been noted that these dogs not only have an inappropriate immune system response but also have skin barrier abnormalities.

Allergy testing can be used to determine the underlying trigger that a pet is reacting to. Two main types of allergy testing are intradermal (skin) and blood (serum). For example, in a 2014 study, researchers found a high sensitization rate to common environmental allergens, with 61.4% indicating sensitivity to dust mites and 46.5% to the common lawn grass Bermuda grass.

While atopic dermatitis is an individual disease, some breeds appear to be affected more frequently. These breeds include Golden Retrievers, Labrador Retrievers, Dalmatians, Scottish Terriers, French Bulldogs, West Highland White Terriers, Boxers, Chinese Shar-Peis, Lhasa Apsos, and German Shepherds.

Food allergies for dogs

Dogs can also have allergies to components in food (sometimes called adverse food reactions). If a dog is allergic to a type of food, they can get skin reactions, gastrointestinal reactions, or both.

Like with canine atopic dermatitis, food allergies are due to an abnormal reaction of the immune system to a substance. While the cause of food allergies is not completely understood, it does require that the dog is exposed to the allergen. A review of several studies determined that the most common ingredients responsible for allergies were: beef, dairy, chicken, and wheat. 

In other studies of 297 dogs, 34% had beef allergies, 17% revealed dairy allergies, 4% were allergic to corn, and 13% showed allergies to wheat.

If a food allergy is suspected, your veterinarian may discuss performing a strict food trial, which is currently the only reliable way to diagnose a food allergy. Unfortunately, skin and blood tests are not proven to be reliable ways to diagnose food allergies at this time. Once a food allergy is identified, your vet may recommend certain dog foods.

Some dog breeds are also more likely to develop food allergies, including Labrador Retrievers, Cocker Spaniels, and West Highland White Terriers.

Food allergies vs. food intolerances

‌When searching for the cause of a dog’s allergic reaction, people commonly interchange food allergies and food intolerances. While food allergies occur due to an abnormal immune response, food intolerances do not involve the immune system.  

Another key difference is that dogs can show intolerance to a food or ingredient the first time they eat it, while they need at least one prior exposure to a food to develop a food allergy.

Common food intolerances could include eating:

  • ‌Too much of one nutrient
  • A diet with too much fat
  • A poisonous or irritating food like chocolate or rhubarb
  • Foods with additives
  • Foods with lactose

‌‌‌Signs that a dog is having an allergic response

1. Skin issues: itching, excessive licking, red and inflamed skin, and hot spots

‌A dog who is itching on the face, belly, groin, rear, base of tail, or side could be showing signs of an allergic response. Because itching can be a sign of atopic dermatitis, food allergies, and flea allergies, this alone does not help us identify the allergen. The location of itchiness can give clues—for example, itching primarily on the back and base of the tail could hint at a flea allergy.

‌Excessive licking is thought to be a sign of itchiness and is one of the most consistent symptoms of dog allergies. It can happen with all allergy types, and it can become so intense that it causes hair loss, bald spots, and areas of raw skin, especially on the rear, back, and sides. Greater concern for flea allergies comes with certain patterns of hair loss or red/raw skin, such as on the rump, tail, and flank.

Dogs can also excessively lick and chew at their toes and paw pads because of allergies. This can be a sign of environmental allergies, but it can also be a sign of food allergies, secondary infections (such as yeast or bacteria), or something else. 

‌Irritated skin quickly turns red and inflamed, and it can feel warm to the touch. Dogs can get red, inflamed skin from any allergy if the itchiness is causing them to lick at themselves excessively and cause trauma to the skin. 

‌Hot spots may resemble red and inflamed skin, but they are larger, painful lesions that often bleed. These spots are often moist as well because of constant licking. As moisture gets trapped underfur, these can worsen and expand in size. Stopping the pet from licking and determining the underlying cause are two important steps for treating these lesions.

2. Repeated ear infections

Ear canals are just modified skin. For some dogs, repeated ear infections could indicate an underlying sensitivity to food or something in the environment.

3. Red, runny eyes

‌Red and runny eyes can happen due to certain environmental  allergies because of the primarily airborne allergens. If your dog develops discharge from the eyes that is yellow or green, has crusty and swollen eyes, or is squinting or pawing at their eyes, you should contact your veterinarian.

4. Vomiting and diarrhea

Vomiting and diarrhea are common signs of food allergies in dogs. Some dogs may also exhibit gastrointestinal noises, flatulence, and soft stools. Dogs can also get vomiting and diarrhea from dietary indiscretion when they eat something they shouldn’t, but this is not considered an allergic response. 

‌5. Swelling and hives

‌Dogs with more severe, acute allergic reactions can get swelling on the face, ears, eyelids, muzzle, or lips. They can also get swelling and inflammation on the paws. This swelling is a direct result of the histamines released and can happen from many types of allergies. If swelling on the face is noted, you should contact a veterinarian as soon as possible.

Hives look more like a rash with raised bumps, and they can appear in response to lots of triggers including insect bites, medications, foods, and more. In dogs, hives can be the only sign or they can be associated with a more severe systemic allergic reaction, called anaphylaxis. If you notice hives, contact your veterinarian.

Guest contributor Emily Clayton smiling against a neutral background.

Emily Clayton Contributor

Emily Clayton has been producing high-quality content since 2013. Her primary expertise and writing interests are in the lifestyle, health, and wellness industries; food culture; and art/design fields, yet she is skilled at content creation for a range of subjects and loves diving into research to produce original, compelling work. With nine years of experience to her name, Emily is a seasoned writer who loves creating content that offers value and an enjoyable reading experience.

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