Scratching, sneezing, hives, diarrhea—these might be signs that your dog has an allergy. But because other health issues can produce these same symptoms, diagnosing allergies can be tricky. An allergy is an abnormal immune response that can be triggered by a variety of substances, like insect bites, pollen, and even food. How do you figure out what’s causing a particular reaction? And if the trigger is something in your dog’s diet, how do you know whether the problem is a true food allergy or a food sensitivity? (We’ll talk about food sensitivities too.)

An allergy is an immune response—more specifically, an exaggerated, abnormal response to something benign that the immune system misinterprets as a threat. The substance that triggers this abnormal immune response is called an allergen.

When it’s functioning properly, the immune system keeps a dog healthy by detecting harmful intruders (like pathogens and parasites) and attacking them before they can cause infection or disease. But in some dogs (and some humans), the immune system has a problem called atopy, which is a predisposition to overreact to certain allergens (whether inhaled, touched, or eaten) as though they were dangerous invaders.
 
When immune cells react incorrectly to something that’s not an enemy—like pollen or meat—they produce antibodies called immunoglobulin E (IgE), which stimulate other cells to release histamine and other chemicals. Histamine creates the inflammation that is typical of allergic reactions, causing redness, swelling, itching, hives, and other uncomfortable symptoms. Once such a hypersensitivity is established, the immune system will have the same overreaction to that particular trigger every time your dog encounters it.

Allergies can cause a wide range of symptoms, many of which can also be caused by other, non-allergy conditions. That’s why it may take time and effort to figure out what’s really causing your dog’s symptoms.
 
Here are some of the most common dog allergy symptoms:
 

• itchy skin, ears, or paws
• hair loss
• hives
• swelling of the face, ears, lips, eyelids, or earflaps
• red, inflamed skin
• saliva staining
• darkening and/or thickening of the skin
• recurrent skin infections, including chin acne
• recurrent ear infections
• sneezing
• itchy, watery eyes
• runny nose
• vomiting
• diarrhea

Allergic reactions can be triggered by an enormous variety of substances. Some allergens are inhaled (like dander and pollen), others are substances that come into direct contact with the skin (like certain plants and medications), and others are ingested (foods). Here are some of the most common types of allergies affecting dogs.

Flea Bite Allergy

The most common allergy in dogs is a hypersensitivity to flea saliva, which causes the immune system to have an extreme response to flea bites. A flea bite allergy can cause intense itching, redness, irritated skin, and hair loss. This reaction is referred to as flea allergy dermatitis.

Other Environmental Allergies

Allergic reactions to other environmental factors are also very common in dogs. Bites from insects other than fleas (like mosquitoes) can cause hypersensitivity responses. Some dogs are allergic to bee stings.

Airborne particles that are common allergy triggers for dogs include house dust mites, animal dander (shed skin cells), plant and tree pollens, and mold spores.

Direct contact with certain substances—including particular plants, plastics (in toys or food bowls), chemicals, and medications—can also cause allergic responses. Itching is the most common symptom of environmental allergies.

Seasonal Allergies

Like human allergies, dog allergies can be seasonal. Maybe you’ve noticed that your dog itches more in the spring and summer, or sneezes a lot in the fall. Those are useful clues: plant pollens and insects, for example, are more prevalent in the warmer months, while mold is more common when the season is cool and damp.

Atopic Dermatitis

Atopic dermatitis in dogs is a chronic itchy skin condition caused by hypersensitivity to one or more allergens. This skin disorder is classified as an allergic condition because it is associated with excessive immunoglobulin E (IgE) production in response to particular allergens, which may be inhaled, touched, or eaten. Atopic dermatitis is fairly common, occurring in roughly 10%–15% of all dogs. (Certain dog breeds may be more likely to develop this condition.)

Food Allergies

Food allergies may not be as common in dogs as airborne allergies; they’re also less common than food sensitivities (which we’ll talk about next). But some dogs do have allergic reactions to one or more ingredients in their diet. The symptoms—including itching, irritated skin, and hives—can look just like those of other allergies, but they don’t vary with the seasons.

Even if you’ve narrowed down the cause of your dog’s symptoms to something in their diet, it may still not be clear whether the problem is an allergy or a sensitivity (sometimes called a “food intolerance”). That’s because these two problems can produce the same symptoms, even though they’re actually caused by two different biological mechanisms.

A true food allergy involves an immune system response: the body’s immune cells attack certain food molecules, mistaking them for dangerous invaders. A food sensitivity, on the other hand, does not involve the immune system. It’s simply an inability to digest a particular food or ingredient.

Lactose intolerance is a familiar example of a food sensitivity: if a dog doesn’t have enough of the enzyme lactase, which is necessary to break down the lactose (a sugar) found in dairy products, then eating dairy will usually be followed shortly by bloating, flatulence, and/or diarrhea. That’s because the dog’s digestive system can’t process dairy correctly.
In dogs, food sensitivities are much more common than true food allergies, which occur in only 1%–2% of all dogs.

In a food allergy, the trigger is usually a basic ingredient in the dog’s diet—most often a protein, but sometimes a carbohydrate. The foods most often associated with allergies in dogs are beef, dairy products, and wheat. Other common allergens are chicken, eggs, lamb, and soy.

A food allergy develops over time, with repeated exposure to a particular allergen leading eventually to symptoms. It might take two years or more for an allergy to produce symptoms in response to a certain food. (A food sensitivity, on the other hand, will produce symptoms right away, since those symptoms are a result of incomplete digestion.)

Like environmental allergens, food allergens cause the immune system to overreact and trigger the release of histamine, which can produce hives, swelling of the muzzle or ears, itching, and many other uncomfortable symptoms.

Genetic predisposition may play a role in why some dogs develop food allergies while others don’t. But the gut microbiome is also a factor. In a healthy gut, the thousands of different kinds of microbes that make up the gut microbiome work together as a diverse, balanced community. But when there aren’t enough beneficial microbes or there are too many harmful ones, the community becomes imbalanced, and some of its important functions stop working.

Allergies actually involve the gut microbiome in multiple ways. For one thing, the gut microbiome houses most of the immune system: 70%–80% of the body’s immune cells live in the gut. When the gut’s microbial populations are out of balance, immune functions stop working properly, making allergic reactions more likely.

Studies have found an association between gut microbiome imbalance and atopic disorders in both humans and animals. When the gut microbiome has too many bacteria from groups that are involved in inflammatory response, that imbalance leads to unhealthy levels of inflammation, which can trigger extreme immune responses throughout the body.

Another result of an imbalanced gut microbiome is increased permeability of the gut lining (a problem sometimes referred to as “leaky gut”). When the gut lining isn’t healthy enough to serve as a strong barrier between the digestive tract and the rest of the body, food molecules can escape from the intestines into the bloodstream. There they can be misidentified and attacked as invaders by the immune system, leading to a hyper-reactive cycle in which the immune system becomes sensitized to those substances and overreacts every time it encounters them.

The good news is that the gut microbiome’s involvement in allergies means that we may be able to resolve an allergy by healing the gut. For example, treatments for atopic dermatitis that target the gut include probiotics and fecal microbiota transplant (FMT).

Learn more about FMT in an oral capsule.

The symptoms of allergies—like irritated skin or diarrhea—can be very uncomfortable for your dog, but allergies are not usually life-threatening.
 
The exception is the kind of acute, severe allergic reaction known as anaphylaxis, which can be fatal if not treated immediately. Anaphylactic reactions are rare in dogs, but they may be caused by food allergens, insect bites, medications, pollutants, and other chemicals. The most common signs of anaphylaxis are itching, hives, facial swelling, excessive drooling, vomiting, and diarrhea. When the reaction involves the whole body, the dog may have difficulty breathing, and the tongue and gums may appear blue.
 
Anaphylaxis is a medical emergency: if you think your dog may be having a severe allergic reaction, seek help immediately.
 
In most cases, allergic reactions in dogs are not dangerous in themselves. However, allergy symptoms can sometimes lead to complications: Environmental allergies can lead to canine atopic dermatitis, a chronic skin disease that requires lifelong management. Itchy, inflamed skin is also vulnerable to secondary infection. And food allergies, by interfering with your dog’s digestion, can lead to malnutrition, as well as imbalances of the gut microbiome.

If your dog is suffering with itchy skin, diarrhea, or other symptoms, how do you know whether the problem is an allergy? Figuring out the root cause may not be easy. For one thing, all the symptoms that can be caused by allergies can also be caused by other health conditions. So your veterinarian may want to test your dog for some of those other issues in order to rule them out.

To complicate matters, hypersensitivity reactions actually fall into several types. What most people think of as the “classic” allergic reaction occurs within seconds or minutes of exposure to the trigger (such as swelling after an insect bite). But other types of reaction take two or three days to produce full-blown effects (such as hives in response to a food allergen).

Allergy Testing for Dogs

Depending on what kind of allergy is involved, an allergy test might help your veterinarian determine what’s causing your dog’s symptoms. Flea bite allergy and many inhalant allergies can often be confirmed with skin tests (similar to those used in humans) or blood tests (which measure antibodies like IgE).
 
Several companies offer hair and saliva tests for both inhalant and food allergies, but studies have found that not all of these tests produce reliable results. This study found that saliva and blood tests for food allergies were unreliable. But some saliva tests for food allergies have shown better accuracy than others.

If your dog is having a severe allergic reaction, you should seek help immediately. But in most cases, allergy symptoms are not life-threatening, just uncomfortable. Fortunately, you can do a lot to help your dog feel better.

Your veterinarian should be able to offer advice about available treatments:

• Immunotherapy (a series of “allergy shots” to desensitize the immune system to a particular allergen)
• Antihistamines (such as benadryl, to counteract the immune overreaction)
• Steroids (to relieve itchiness and irritation)
• Antibiotics (if your dog’s skin has become infected)

In addition to any other measures, it’s important to reduce or eliminate your dog’s exposure to whatever element in their environment or diet is triggering an allergic response.

• Fleas: If your dog is allergic to flea bites, use a safe year-round treatment to keep fleas away.
• Airborne particles: If the trigger is something in the air (like pollen or dander), you may be able to reduce the number of allergen particles your dog encounters by vacuuming more often, using an air cleaner/purifier with HEPA filtration, or washing your dog with a therapeutic shampoo.
• Foods: For suspected food allergies, the first step is typically an elimination diet.

Elimination Diet

The best way to identify the particular ingredient that’s triggering symptoms is to stop feeding all the foods your dog has already been exposed to and transition to a diet containing only novel ingredients (foods your dog has never eaten before—perhaps duck, rabbit, lamb, or even crickets). Your veterinarian should be able to help you plan an appropriate elimination diet.
If your dog’s symptoms disappear after some time on the new diet, you can be fairly sure the problem was a food sensitivity or allergy. After three months of feeding the new diet, you can reintroduce one food at a time from the previous diet to see whether your dog’s symptoms return. If symptoms don’t reappear within two weeks, that particular food is no longer a suspect.

Other Dietary Changes

Once you have identified and eliminated the particular food that triggered your dog’s symptoms, you can establish a new diet that avoids that ingredient while still providing all the nutrients your dog needs. Current science recommends a high-protein, balanced diet that includes fiber and fatty acids (which have anti-inflammatory properties).

While no food is truly “hypoallergenic,” some dogs can benefit from commercially available hydrolyzed diets—in which the animal protein has been broken down into molecules small enough that they are unlikely to cause an immune response. And a rotational diet can help prevent future food sensitivities or food allergies by limiting your dog’s exposure to the same ingredients over time.

Gut Health Test

Gut Microbiome Testing can give you important clues about what might be causing your dog’s symptoms. Our at-home Gut Health Test for dogs can detect bacterial imbalances and identify problematic groups of bacteria associated with inflammation and allergic conditions.

For example, high levels of Sutterella bacteria in the gut microbiome are associated with food sensitivities. Oscillospira bacteria tend to be deficient or absent in pets with severe food allergies. Clostridiales bacteria are known to prevent “leaky gut syndrome” and are associated with a decreased risk for developing environmental and dietary allergies, so these important gut bacteria are often missing in a dog with allergies. There is even some evidence that introducing Clostridiales (via FMT) can decrease or resolve allergic symptoms.

Fecal Transplants

A fecal microbiota transplant (FMT), also called a fecal transplant, is a way to transfer a complete set of healthy, species-appropriate gut microbes from a healthy donor to a sick recipient. By delivering a diverse, balanced community of beneficial bacteria, FMT can resolve a variety of symptoms associated with imbalance or dysfunction of the gut microbiome—including various immune system issues, skin problems like atopic dermatitis, and digestive disorders like inflammatory bowel disease (IBD).

If your dog is missing important beneficial bacteria—for instance, after a course of antibiotics—FMT can fill in those missing groups, restoring balance to the microbiome and strengthening its immune functions. And with our Gut Restore Supplement oral FMT capsules, your dog can get the benefits of FMT without sedation or expensive procedures.

Boost Your Dog’s Immune System

You can also give your dog’s immune system a healthy boost with DoggyBiome™ ImmuneShield™ chews. The active ingredient is a proprietary formulation of postbiotics specifically designed to improve immune function in dogs, address seasonal allergies, and promote gut health. By reducing systemic inflammation and promoting beneficial gut bacteria, ImmuneShield resolves certain itchy skin conditions and improves gastrointestinal symptoms. (And dogs love these chews: they’re trout-flavored!)

• An allergic response occurs when the immune system overreacts to something benign—like pollen or food—as though it were a dangerous invader.
• The most common allergy triggers in dogs are flea saliva and airborne particles (especially house dust mites, dander, plant pollens, and mold spores).
• A food allergy is different from a food sensitivity: a food allergy produces an immune response, whereas a food sensitivity is an inability to correctly digest a particular ingredient.
• True food allergies are uncommon in dogs, but many dogs develop food sensitivities, especially when they eat the same diet for a long time.
• Because 70%–80% of your dog’s immune cells live in the gut, problems with the gut microbiome can lead to improper functioning of their immune system.
• An imbalanced microbiome can cause the gut lining to become “leaky” and allow food molecules to escape. Once outside the digestive tract, these molecules may be attacked as invaders by the immune system.
• An elimination diet is the best way to identify which foods are triggering your dog’s symptoms.
• Probiotics, postbiotics, and FMT can improve allergies by targeting the gut.