- Not a substitute for professional veterinary help.
If your dog suddenly starts scratching constantly, sneezing, or breaking out in hives, they could be having an allergic reaction. Dogs with allergies most often begin experiencing symptoms between ages one and three.
An allergic reaction occurs when a dog’s immune system overreacts to a trigger, called an allergen, that’s typically harmless, explains Dr. Shannon Barrett, veterinarian and owner of Downward Paws.
Allergens can include foods, insect bites or stings, substances that irritate the skin, pollen, dust mites, and mold.
If your dog has symptoms of an allergic reaction, it’s important to take them to the vet as soon as possible, Dr. Barrett says. In rarer cases of anaphylactic shock, seek immediate medical help from an emergency pet hospital.
Read on to learn more about dog allergic reactions and the best way to support a pup with allergies.
Symptoms of Allergies in Dogs
Allergy symptoms can appear any time of year, says Dr. Kyla Jackson, veterinarian and dermatology resident at Missouri Veterinary Dermatology Center.
That said, symptoms of seasonal allergies typically only show up during peak times for certain pollens, molds, and other environmental triggers.
Mild to moderate symptoms
Signs of a mild to moderate allergic reaction may include:
- Itchy skin: Dogs may scratch, lick, chew, or rub their skin against surfaces in an attempt to relieve discomfort.
- Hives: These raised, red bumps appear suddenly and often cause itchiness. They’re easier to spot on dogs with short or thin coats.
- Facial swelling: Puffiness around the eyes, muzzle, or lips tends to develop quickly after exposure to an allergen.
- Red, inflamed skin: Your dog’s skin may appear red, swollen, warm, and tender to the touch.
- Gastrointestinal issues: Vomiting, diarrhea, or gas often shows up along with skin symptoms.
- Sneezing and coughing: Airborne allergens like pollen, mold, or dust may cause respiratory symptoms.
- Watery eyes or nasal discharge: Along with sneezing or coughing, dogs may also have clear fluid draining from the eyes or nose.
- Itchy ears: Inflammation or infection in the ear canal may lead your dog to shake their head or scratch their ears frequently.
- Loss of fur: Repeated licking, chewing, or scratching can lead to patches of bald or thinning hair.
Severe symptoms
Anaphylactic shock is a severe allergic reaction and is a life-threatening emergency. Signs usually appear within seconds to minutes after exposure to an allergen.
Common signs of anaphylactic shock include:
- Diarrhea
- Vomiting
- Excessive drooling
- Pale gums
- Cold limbs
- Trouble breathing
- Lethargy
- Abnormal heart rate
- Seizures
- Coma
Seek immediate care from a vet if your dog shows any of the above signs.
What Causes Allergic Reactions in Dogs?
Common substances that trigger allergic reactions in dogs include:
- Environmental allergens: Pollen, mold, dust mites, or grass can cause seasonal or year-round itching, sneezing, and skin irritation. Reactions are usually mild to moderate but can occasionally be severe.
- Food allergies: Reactions to certain proteins or ingredients—beef and dairy are the two most common food allergens— can lead to skin problems, ear infections, and gastrointestinal upset. Severe reactions are rare, but when they occur, they can be life-threatening.
- Fleas: Flea saliva can trigger flea allergy dermatitis, leading to intense itching, redness, and hair loss, often on the lower back and tail base. Reactions are usually mild to moderate but can cause severe skin infections if left untreated.
- Other insect bites and stings: Bites and stings from ticks, mosquitoes, bees, or wasps can lead to localized swelling and intense itching. In rare cases, a sting may trigger a serious allergic reaction.
- Contact allergens: Chemicals in cleaning products, certain fabrics, or plants like poison ivy can cause redness, rash, or irritation where the skin touches the allergen. Reactions are generally mild unless a secondary infection develops.
- Medications and vaccines: Some dogs may react to specific drugs or vaccines, with symptoms ranging from mild swelling to life-threatening anaphylaxis.
How To Treat Allergic Reactions in Dogs
The best treatment for an allergic reaction depends on the type and severity of the allergy, Dr. Barrett says. Common treatment approaches include:
Visit the vet
If your dog has any signs of a severe allergic reaction, take them to an emergency pet clinic immediately. If you don’t know how serious their condition is, call your vet or the nearest emergency clinic for guidance.
For mild, moderate, or ongoing symptoms, schedule an appointment with your regular vet. They’ll examine your dog, review their medical history, and may recommend blood work, skin scrapings, or intradermal allergy testing.
Dr. Jackson explains that this process includes ruling out other medical conditions with similar symptoms, identifying triggers, and creating a tailored treatment plan.
Try hypoallergenic shampoo
Use a gentle, fragrance-free shampoo formulated for sensitive skin to help wash away allergens like pollen, dust, and dander. This can often help ease symptoms within a few baths, though you may need to keep using it if your dog has chronic allergies.
Use antihistamines, with guidance from a vet
Antihistamines like diphenhydramine (Benadryl) or cetirizine (Zyrtec) can reduce itching, swelling, and hives by blocking histamine, the chemical responsible for many allergy symptoms. Most of these medications will begin working within an hour or two.
The correct dosage and frequency will depend on your dog’s size and health, so it’s important to ask your vet before giving your dog any medication.
Ask your vet about Apoquel or Cytopoint
Allergy injections like Cytopoint and oral medications like Apoquel can help control itching and inflammation by targeting the immune response that drives allergy symptoms.
Cytopoint is typically given every four to eight weeks, while Apoquel is taken daily. Both can start providing relief within hours to days, but dogs will usually need ongoing treatment to manage long-term symptoms.
Use targeted supplements for allergy support
Certain supplements, including omega-3 fatty acids, probiotics, and quercetin, can help support skin health, reduce inflammation, and strengthen the immune system.
Dogs typically take these supplements once a day, and it may take several weeks to get results. Supplements work best as part of a long-term allergy management plan, not alone. Always ask your vet about supplements before giving them to your dog.
Try an elimination diet
An elimination diet involves feeding your dog a limited-ingredient or hydrolyzed protein food for up to 12 weeks to determine if a food allergy or sensitivity is the cause. If their symptoms improve, you can reintroduce potential allergens one at a time to find the specific trigger.
To get accurate results, it’s best to try an elimination diet only with guidance from your vet.
Consider immunotherapy
Vets may recommend immunotherapy for dogs with severe or long-term allergies. This approach involves exposing your dog to small amounts of the allergen via injections or oral drops to help their immune system become less reactive over time.
It may take several months to get results, but this treatment is the only method that targets the root cause of allergies. Immunotherapy can provide long-term relief for many dogs.
How To Prevent Allergic Reactions in Dogs
While you can’t always prevent allergic reactions, creating an allergy-friendly lifestyle can go a long way toward reducing your dog’s exposure to allergens and keeping flare-ups at bay. Here’s how to get started:
- Use consistent flea and tick prevention: Monthly oral or topical treatments are essential, especially for dogs with flea allergies.
- Bathe regularly: Bathing your dog every two to four weeks with a hypoallergenic shampoo can remove allergens and soothe their skin.
- Wipe your dog’s paws and coat after outdoor time: Use pet-safe wipes or a damp cloth to remove pollen and other irritants, especially during allergy season.
- Keep your home clean: Vacuum weekly, wash bedding in hot water, and consider using a HEPA air purifier to reduce dust, dander, and mold.
- Use pet-safe cleaning products: Harsh chemicals can irritate sensitive skin. Opt for fragrance-free or pet-friendly options.
- Feed a high-quality, balanced diet: Good nutrition supports skin health and immune function. If your dog has known food allergies, stick to their prescribed diet and avoid reintroducing trigger ingredients.
- Support with allergy supplements: Fish oil and other supplements may help reduce inflammation and improve skin resilience over time.
- Stay on top of vet visits: Routine vet visits help detect allergy symptoms early and allow your vet to adjust treatment plans as needed.
Dog Allergic Reaction FAQs
What’s the difference between an allergic reaction and anaphylactic shock?
An allergic reaction can range from mild itching and sneezing to moderate swelling or digestive upset. Anaphylactic shock is a severe, life-threatening allergic reaction that causes rapid-onset symptoms, like difficulty breathing, collapse, pale gums, or a sudden drop in blood pressure. Anaphylaxis requires immediate emergency veterinary care.
Can I give my dog Benadryl for an allergic reaction?
Some human allergy medicines, like Benadryl, can be safe for dogs if given correctly, explains Dr. Renee Schmid, senior veterinary toxicologist at Pet Poison Helpline. But always check with your vet first.
How long will my dog’s allergic reaction last?
The duration of a dog’s allergic reaction depends on the cause and severity. Mild reactions may resolve within a few hours to a couple of days once the trigger is removed or treatment begins. More severe reactions or chronic allergies may take longer to manage and often require ongoing treatment to keep symptoms under control.
Will my dog’s allergic reaction go away on its own?
Some mild symptoms may improve without treatment, but allergic reactions can worsen quickly or lead to complications like skin infections. Always consult a vet to identify the cause and prevent repeat or more severe episodes.
Are more dogs getting allergic reactions than before?
Research suggests that flea and environmental allergies are on the rise. Experts don’t fully understand the exact cause, but this could relate to factors like changing climates, increased exposure to indoor allergens, or improved veterinary awareness and diagnosis.
