6 Signs Your Dog Is Having an Allergic Reaction

Allergic reactions in dogs occur when the immune system overreacts to what should be an innocuous stimulus called an allergen, such as pollen, food, an insect sting, or medication. A dog’s allergic reaction can range from mild, such as a little itching, to severe and life-threatening, like anaphylaxis.  

Recognizing the early signs of a dangerous allergic reaction in dogs—such as facial swelling, vomiting, excessive scratching, or difficulty breathing—can help you act quickly and protect your dog’s health. If you think your dog is having an anaphylactic reaction, seek immediate veterinary attention.  

Common Causes of Allergic Reactions in Dogs

Dogs can be allergic to a wide range of triggers, including: 

• Environmental allergens: Pollen, dust mites, mold, and grass  

• Bug bites or stings: Fleas, mites, bees, spiders, and mosquitoes  

• Food ingredients: Common proteins like chicken, beef, and dairy  

• Medications or vaccines: Some dogs react to specific drugs  

• Contact allergens: Chemicals, materials, or plants that touch the skin 

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. Recognizing the signs as quickly 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. Although itching can occur anywhere, common areas affected by allergies include the face/head, ears, paws, belly, skin folds, and hind end. 

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

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:  

• Avoidance and hyposensitization: Whenever possible, it’s best to avoid contact with what triggers a dog’s allergic reaction (a specific drug, for example). When avoidance isn’t realistic, as is the case with seasonal allergies to pollen or grass, hyposensitization (immunotherapy or allergy shots) can be a good option. 

• Flea and tick prevention: Fleas bites can make any dog itchy, but the scratching and biting can be extreme in dogs with flea allergies. Make sure your pup does not have fleas and is on a routine, vet-recommended flea and tick medication for dogs, like Credelio or NexGard. 

• Medicated shampoos and topicals: Medicated shampoo, like Douxo S3 Calm, can remove allergens from a dog’s coat and skin and help soothe itchy skin. Medicated topical products, like Vetericyn Plus, can help treat a minor skin infection or associated wounds. 

• Anti-itch medications: Prescription medications like Zenrelia are used to manage allergic itching. A single daily dose of Zenrelia can help to quickly relieve itching in dogs over 12 months. Other options include prednisone, Atopica, Apoquel, and Cytopoint. 

• Diet change: Food allergies are managed with a diet that doesn’t contain the dog’s specific allergen, which is typically a protein, or that is made with hydrolyzed proteins like Purina Pro Plan Veterinary Diets HA Hydrolyzed Chicken Flavor Dry Dog Food.  

• Nutritional supplements and antihistamines: Omega-3 fatty acids like Nutramax Welactin Omega-3 Fish Oil and antihistamines, including PetArmor Antihistamine Medication for Allergies for Dogs, are enough on their own, but can be helpful when combined with other treatments for allergies in dogs. 

2. Hives  

Hives are raised red welts on a dog’s skin, most often caused by an allergic reaction. They can develop anywhere on the body but are most commonly seen on the face, legs, back, and sides. 

Hives can last from seconds to hours and may appear and disappear quickly. They are usually itchy, though some seem to cause little irritation. 

In dogs with thick or extra-hairy coats, hives may look different—appearing as patches of raised fur rather than visible red skin, since the inflammation is hidden beneath the coat. 

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 (diphenhydramine) can be helpful if your vet says it’s OK for your dog. 

3. Facial Swelling  

An allergic reaction can also cause facial swelling. Typically, this swelling occurs around the:   

• Eyes  

• Ears  

• Nose  

• Muzzle   

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

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

• Bee stings  

• Bug bites  

• Certain foods 

• Toxin exposure 

• Medications   

• Vaccinations 

Mild facial swelling is treated similarly to hives, with both topical remedies and oral medications, but severe cases require immediate veterinary support and injectable medications.   

4. Stomach Upset  

Stomach upset can be associated with a food allergy, but it may also be seen with other potential allergens. Dogs usually have itchy skin as well as symptoms of stomach upset like:  

• Vomiting  

• Diarrhea  

• Decreased or total loss of appetite  

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

Food allergies are treated long-term with a hypoallergenic diet 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 immediately.  

5. Respiratory Problems  

Common respiratory symptoms of an allergic reaction in dogs include:   

• Sneezing  

• Coughing  

• Wheezing  

• Lethargy  

• Trouble breathing  

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

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

Noisy or labored breathing can also be seen, especially in brachycephalic (smoosh-faced) dog breeds.   

If your dog is having respiratory symptoms, take them to the veterinarian. And if they’re having trouble breathing, take them to the nearest emergency vet. Oxygen therapy, steroid injections, and other injectable medications 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 histamines and other dangerous inflammatory chemicals that can cause the body to go into shock. These substances 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 or blue 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. It can occur within minutes and is a serious medical emergency that needs to be treated right away.   

Veterinarians may treat anaphylaxis with IV fluids, a breathing tube, oxygen therapy, and IV medications like epinephrine, dexamethasone, and more.    

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: Zenrelia, Atopica, and Apoquel are effective oral medications that can help treat environmental allergies. 

• Steroid medication: Prednisone is a common oral medication, while dexamethasone is more commonly given 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, Convenia, or other antibiotics can be used for a skin infection. 

• Supplements: Probiotics can be used to help support gut and skin health and omega-3 fatty acids have proven anti-inflammatory effects. 

• 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 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. 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.