6 Signs Your Dog Is Having an Allergic Reaction

Allergic reactions in dogs can appear in many ways as the immune system overreacts to a stimulus or allergen. From a mild skin irritation to a life-threatening situation that affects breathing, like anaphylaxis, the severity is dependent on the specific allergen and your dog's sensitivity. 

Allergic reactions in dogs can be caused by a variety of triggers—some more serious than others. Bee stings, bug bites, medications, vaccines, food, and environmental agents such as pollen, dander, grass, and dust mites are among the most common causes of allergic reactions in dogs.  

Seasonal and severe allergies can cause allergic reactions as well. These allergens can be inhaled, ingested, applied directly to the skin, or absorbed through the skin on contact. 

Learn the signs of an allergic reaction in dogs, how veterinarians treat them, and more. 

If you think your dog is having an allergic reaction, seek veterinary attention. 

6 Signs of Allergies in Dogs

Knowing the signs of an allergic reaction in dogs and understanding what your next steps should be will help immensely in your pup's time of need. Observing the signs as soon as possible ensures you can provide immediate medical attention if necessary.  

Here’s what to look for to determine if your dog is having an allergic reaction: 

1. Itchy Skin and Excessive Scratching 

Itchy skin is the most common symptom of allergic reactions in dogs.  

When a dog is itchy, excessively scratching, licking, or rubbing the skin can damage the skin barrier. This creates an ideal environment for bacteria and yeast—organisms that normally live on the skin in small numbers—to multiply and cause infections. 

These infections can lead to symptoms like hair loss, redness, scabs, bumps, and skin irritation. Licking can also introduce bacteria from the mouth to already irritated skin, worsening the infection.  

This can result in more scratching or licking, which can lead to further skin damage such as abrasions or open wounds.  

While itchiness can occur anywhere or all over the body, these are the most common places dogs get itchy from allergic reactions: 

• Face/head 

• Ears 

• Paws 

• Belly 

• Skin folds 

• Hind end 

Just about any underlying cause of an allergic reaction can cause itchiness and excessive scratching in dogs. You have to treat the symptoms and the underlying cause for the itch to stop. Treatment may include: 

• Flea and tick prevention: Make sure your pup does not have fleas and is on a routine flea and tick prevention.  

• Medicated shampoo: Medicated shampoo, like Douxo S3 Calm, can help soothe itchy skin. Between baths, medicated mousse and wipes—like Douxo S3 PYO mousse and Duoxo S3 PYO wipes—or anti-itch spray, like Relief Spray, can also help provide relief. 

• Medicated topical products: Medicated topical products, like Vetericyn Plus, can help treat a minor skin infection or associated wounds.  

• Oral medications: Your veterinarian might also recommend oral medications or a diet change. 

2. Hives 

Hives (also called urticaria) are raised red welts on a dog’s skin. Hives can last seconds to hours and can sometimes appear as quickly as they resolve. Hives are often very itchy, but some allergens are less irritating than others and might not be overly itchy. 

The most common cause of hives in dogs is an allergic reaction.  

Some extra-hairy dogs, or those with an undercoat of thick fur, might have welts that appear slightly different. These welts can appear like patches of fur sticking up or swollen, as you are only seeing the inflammation and not the skin directly.  

Hives can occur anywhere on the body, but the most common locations in dogs are:  

• Face 

• Legs 

• Back 

• Sides  

As long as there are no other symptoms, persistent hives should be treated by:  

• Bathing your dog to remove any possible allergen 

• Taking your dog to the vet for a checkup, where they will likely give medication, such as prednisone or an antihistamine, to lessen the immune system response 

• A dose of oral Benadryl can be helpful if you cannot see the vet right away 

3. Facial Swelling 

When your fuzzy family member returns from a jaunt outside and their face is swollen, it can be quite an alarming sight.  

An allergic reaction can cause facial swelling as an inflammatory response to an allergen. Typically, this swelling occurs around the:  

• Eyes 

• Ears 

• Nose 

• Muzzle  

And most commonly, facial swelling is caused by an allergic reaction to: 

• Bee stings 

• Spider bites 

• Insects 

• Medications  

• Burrowing into the ground  

Facial swelling is treated similarly to hives, with both topical remedies and oral medications.  

It’s important to note that facial swelling can quickly progress to breathing problems if the throat is swollen as well. Any change in your dog’s breathing warrants an immediate vet visit. 

4. Stomach Upset 

Stomach upset is most often associated with an adverse reaction to food, but it can be from any potential allergen. Symptoms of stomach upset include: 

• Vomiting 

• Diarrhea 

• Decreased or total loss of appetite 

This immune-system reaction to food is more common over an extended period, rather than right away like other symptoms of an allergic reaction in dogs.  

Proteins are usually the culprit of food allergies, with chicken, beef, and dairy being the most common.  

Food allergies are treated long-term with a hypoallergenic diet trial using a novel-protein, limited-ingredient, or hydrolyzed dog food. Your veterinarian may also recommend probiotics, antibiotics, or antinausea medications to treat the symptoms. 

Vomiting and diarrhea can also be a symptom of anaphylaxis, which is life-threatening and should be treated in a timely manner. 

5. Respiratory Problems 

Common respiratory symptoms of an allergic reaction in dogs are similar to a cold or the flu in people. They include:  

• Sneezing 

• Coughing 

• Wheezing 

• Lethargy 

• Trouble breathing 

These symptoms often arise from inhaled allergens, such as those allergens associated with environmental allergies.  

Sneezing, coughing, and wheezing often come first and can lead to trouble breathing.  

Noisy or labored breathing can also be a sign of a struggle, especially in brachycephalic (smoosh-faced) dog breeds.  

If your dog is having respiratory symptoms, take them to the veterinarian right away. And if they’re having trouble breathing, take them to the nearest emergency vet. Oxygen therapy, steroid injections, and injectable allergy medication are often needed to treat these symptoms of an allergic reaction in dogs.  

6. Anaphylaxis 

Allergic reactions can range from mild to life-threatening—the most severe being anaphylaxis.  

During anaphylaxis, the immune system is stimulated to produce dangerous chemicals that cause the body to go into shock. These chemicals have a widespread effect on many areas of a dog’s body, including: 

Cardiovascular and respiratory systems 

• Stomach and intestinal tract 

• Skin  

• Nervous system 

• Eyes 

Symptoms of anaphylaxis include: 

• Pale gums 

• Lethargy 

• Weakness or collapse 

• Tremors 

• Loss of consciousness 

• Cardiac arrest 

• Low blood pressure 

• Difficulty/labored breathing 

• Vomiting 

• Loss of bowel/bladder control  

Anaphylaxis can be caused by any allergen and can happen in any dog at any time. It occurs within minutes and is a serious medical emergency that needs to be treated right away.  

Veterinarians treat anaphylaxis with IV fluids, epinephrine, and IV steroids like dexamethasone. Severe inflammation in the airway may require a breathing tube, sedation, and even a ventilator to ensure your dog can breathe.   

How Vets Treat Allergic Reactions in Dogs

Allergic reactions in dogs are treated in a variety of ways, depending on the underlying cause and the symptoms. Treatments may include: 

• Antihistamines: Antihistamines are used for mild allergic reactions (e.g., Benadryl). 

• Medicated topical products: Shampoos, wipes, mousse, and sprays containing anti-inflammatory, antibiotic, antifungal, and soothing properties can be helpful for allergic reactions causing itchy skin. 

• Allergy medication: Apoquel is an effective oral medication that can help treat environmental allergies. 

• Steroid medication: Prednisone is a common oral medication, while dexamethasone is common as an injection. Both are used for their anti-inflammatory effects and their immune suppression. 

• IV fluids and injectable medications: Epinephrine can be used for anaphylaxis. 

• Antibiotics: Cephalexin or Convenia can be used for a skin infection, while metronidazole can be given to help treat significant diarrhea. 

• Probiotics: Probiotics can be used to help support gut and skin health. 

• Flea and tick prevention medications: Routine, year-round flea and tick prevention helps prevent itchy skin and allergic reactions for dogs allergic to fleas. 

• Cool compress: This can be used for insect bites or bee stings. 

How To Prevent Allergic Reactions in Dogs

Ways to help prevent allergic reactions in dogs at home depend on the allergen that stimulated the reaction.  

Identifying and removing allergy triggers is the most important step to preventing future allergic reactions. And intradermal allergy testing is the best way to determine which environmental allergens your dog is allergic to. This is done by a veterinary dermatologist, and they use the results to make a special allergy vaccine to prevent allergic reactions in your dog.  

Unfortunately, allergy testing is only for environmental allergies, not food allergies. Other types of allergy testing—including blood, hair, and saliva testing in dogs—is not accurate.  

Here are some ways to help prevent allergies in your dog: 

• If your dog reacts to pollen, wipe them down with dog-friendly wipes, like Earth Rated wipes, after outdoor walks—especially the paws, where dogs tend to lick.  

• Use HEPA air filters, like Honeywell filters, to reduce indoor allergens.  

• Ensure your dog is on a year-round flea and tick prevention, like Simparica chewables or Bravecto topical. This helps prevent itchy skin and allergic reactions in dogs allergic to fleas.  

• Document anaphylactic reactions in your dog’s medical record, and going forward, take proper precautions with medications and vaccines.