How to Treat Allergic Reactions in Dogs

English Bulldog Puppy Watching a Bumblebee

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Just like people, dogs can have allergies to a variety of things. This means that their immune system can be extra sensitive to various types of allergens. Usually when people speak about allergies in dogs, they are referring to a food allergy or something called canine atopic dermatitis. Unfortunately, dogs can also experience acute allergic reactions. Often, when your dog has an allergic reaction to something you won't know what caused the reaction—just that there is one.

What is an Allergic Reaction?

An allergic reaction is an overreaction of the immune system to something that it is exposed to. This can be something a dog eats, venom from a bee sting, pollen, a vaccine, or any number of other things. Some allergic reactions present as chronic skin issues or GI upset. An acute allergic reaction can be more concerning, although most dogs have mild symptoms that area easily treated. The offending allergen may never be pinpointed, but whether it is environmental, chemical, or pharmaceutical, the hallmark symptoms are the same.

Signs of Allergic Reactions in Dogs

Clinical symptoms of an acute allergic reaction in a dog are clear and straightforward.


Swelling of the Face



Red, warm skin


Facial swelling is the most common and most obvious symptom of an acute allergic reaction. Some brachycephalic breeds, such as pugs, bulldogs, and Boston terriers may have increased trouble breathing due to this swelling. Hives might be harder to see on certain breeds, depending on their fur. They're easier to see in short-fur breeds, such as boxers, pit bulls, etc. and they appear as bumps all over the dog. Pruritus, the medical term for itchiness, can be associated with the inflammatory response. Restlessness comes from just feeling uncomfortable from the hives and swelling. Redness and warmth of the skin derives from the inflammatory reaction throughout the body.

In a severe acute allergic reaction, also known as an anaphylactic reaction, vomiting, diarrhea, collapse, pale gums, and shock may be seen. These symptoms happen quickly and are usually not accompanied by facial swelling and hives. This is an emergent situation, and veterinary medical attention should be sought out immediately.

Causes of Allergic Reactions

An allergen that can cause an acute allergic reaction in dogs, as previously mentioned, can be environmental, chemical, or pharmaceutical.

  • Bug Bites/Stings
  • Pollens
  • Molds
  • Food
  • Household Cleaners
  • Air Fresheners
  • Medications
  • Vaccines

In years past, it was quite common for small breed dogs to have an allergic reaction to the Leptospirosis vaccine. Pharmaceutical companies have come a long way, though, in making more pure vaccines. While vaccine reactions can still occur, it's much less common. Leptospirosis is a bacterial infection that can cause kidney failure in dogs and people. That means getting this vaccine for your dog protects both of you.

Diagnosing an Allergic Reaction in Dogs

Determining that a dog is having an allergic reaction is based off of clinical symptoms and the patient's history. Things like recent (i.e. earlier that same day) vaccines, time outside, any new air fresheners or diffusers, etc. can help pinpoint when or what kind of allergen a dog is reacting to.

Treatment of Allergic Reactions

Your veterinarian will threat most allergic reactions the same regardless of the allergen. They might use an injection of an antihistamine, such as diphenhydramine (Benadryl) as well as an injection of a corticosteroid, such as dexamethasone. In rarer, more severe cases, additional therapeutics, such as oxygen supplementation and epinephrine, and additional monitoring of blood pressure as well as heart rate and rhythm may be warranted.

Prognosis of Dogs with Allergic Reactions

Most allergic reactions aren't life-threatening if your dog receives immediate veterinary attention. Although Benadryl is safe for dogs, the injectable form takes effect much more quickly than oral, providing relief sooner. If your dog has a brachycephalic confirmation and/or concurrent Brachycephalic Airway Syndrome, they are at increased risk for issues with overheating and worsening breathing problems due to their airway issues.

How to Prevent Allergic Reactions

Because not all dogs react the same to an allergen, preventing a reaction can be tricky. Avoid suddenly switching products, such as carpet cleaners or detergents that you may use to clean your dog's bedding and sleeping area. Keep a close eye on your dog while they are outside. Take heed if you have bees, wasps, or other stinging insects in your area. If your dog does have a history of vaccine reactions, your vet may split up vaccines so they aren't all done at once and/or they may give an injection of diphenhydramine before the vaccine is given. This can help prevent a vaccine reaction from occurring.

Acute allergic reactions can be scary, and if left untreated, serious. Oftentimes, though, a simple treatment is all that is needed to get your dog feeling better. If you have any questions about your dog's risk for an allergic reaction—especially a vaccine reaction—speak to your veterinarian.