Severe Allergic Reactions in Dogs

Luckily, severe IgE allergic (anaphylactic) reactions are rather rare in dogs. Despite practising in a range of clinics, including emergency clinics, we see only a handful of cases of truly anaphylactic reactions each year.

If your dog is having a severe allergic reaction, time is of the essence when seeking veterinary care and administering treatment. Sadly, untreated anaphylactic shock can be fatal, and it is a rapidly progressing condition.

Thankfully, the treatment is nearly always curative, with dogs responding within a matter of minutes.

What is a Severe Allergic Reaction in Dogs?

A severe allergic reaction involves IgE antibodies that bind to mast cells and other white blood cells, leading to the release of large amounts of histamine.

What is the Difference Between a Mild Allergy and Anaphylaxis?

Mild allergies are different to anaphylaxis, and much more common. Signs manifest more slowly and usually occur a few hours or days after contact with the allergen.

Symptoms can include itchy skin, runny poos, bloating, and ear infections.

Signs of a Severe Allergic Reaction in Dogs

If your dog begins to experience a severe allergic reaction, the symptoms usually occur within minutes of exposure to the allergen and become rapidly very serious.

Facial Swelling

Often swelling affects the eyes, muzzle, face and neck, and your dog may appear puffy.

The classic case would be a pet that is stung by a bee on its mouth or nose and then develops massive localised swelling. The danger with facial or neck swelling is that it can quickly affect your dog’s breathing.

Hives or Rapid Skin Swelling

Hives are also referred to as ‘nettle rash’, and they can appear all over the skin. These are raised bumps which are typically very itchy. In addition to hives, the skin may be red and mildly swollen all over.

Difficulty Breathing

As the airways swell, the dog struggles to inhale enough air, resulting in wheezing and laboured breathing.

They may start to breathe very quickly and to stand with their neck stretched and their elbows wide, in an attempt to take in more air.

Coughing may occur, and the mucous membranes may become cyanotic (blue) as oxygen levels drop.

Vomiting or Diarrhoea

Vomiting and diarrhoea commonly occur thanks to the large amount of histamine in the bloodstream. Dogs may also drool and fart.

This stomach upset has a rapid onset, and dogs often won’t make it outside, as they have little control.

Weakness or Collapse

The effect of histamine on the blood vessels is that they dilate, which means your dog’s blood pressure will suddenly dip dangerously low, and they will feel weak, lethargic, and woozy.

There will also be a reduced blood flow to the extremities, such as the paws, which may feel cool to the touch.

As the body attempts to counteract this drop in blood pressure, you may notice your dog’s heart rate is racing.

What Causes Severe Allergic Reactions in Dogs?

Several things can cause severe reactions, and the trigger varies from one canine to another.

Insect Stings or Bites

One of the more common causes of canine anaphylaxis we see in the UK is insects such as wasps or bees.

Stings usually occur on the face or front paws when the dog is outside, while chasing or batting at a flying insect.

Food Allergies

In dogs, food allergies nearly always cause non-IgE (non-life-threatening) allergic reactions, like itchy skin and an upset stomach.

However, a small number of dogs will have anaphylactic food allergies and will react within minutes of eating the food. Any food can be a culprit, and I’ve personally witnessed dogs reacting to chicken, peanuts, and dairy.

Vet Note: This is different to toxic or poisonous foods, such as chocolate or raisins. Every dog will become sick from exposure to large amounts of these foods, but this is not due to an allergic reaction.

Medications or Vaccines

A dog can react to any sort of medication or vaccination. Documenting the reaction is hugely important, so the medicine can be avoided completely in the future.

With regard to vaccines, dogs may be allergic to one brand but not another, due to the adjuvant used.

Environmental Allergens

It is really rare that environmental allergens like pollen or dust mites would cause anaphylaxis, and they are much more commonly linked to ongoing ill health and signs like skin rashes, itchy eyes, and sneezing.

Potentially, if a highly sensitised dog has a large exposure to one of these allergens, they could go into anaphylactic shock. This would be more likely in a dog with damaged skin.

Contact Allergens

Another consideration would be chemicals such as cleaning products, pesticides or flea and tick medicine that come into contact with the skin.

The reaction would generally begin at the site of contact, but can then spread to affect the whole body.

Is a Severe Allergic Reaction in Dogs an Emergency?

There is no doubt that anaphylaxis is a true emergency that requires an immediate response.

When Should You Go to the Emergency Vet Immediately?

If you suspect your dog is experiencing a true, severe allergic reaction, contact your local emergency vet immediately- regardless of the time or day.

What to Do If Your Dog Has a Severe Allergic Reaction

If you believe your dog is reacting to something, you’ll want to jump into action right away.

What Should You Do at Home Before Seeing a Vet?

The first thing to do is identify and remove the inciting cause. This can mean taking away any food that was recently eaten or bringing your dog inside. If you believe your dog had contact with something on their skin, wash it off immediately.

If there is an insect stinger, try scraping it out with a credit card (or similar). Squeezing could lead to greater venom injection and increased histamine release.

Call your nearest vet and start the journey to get there. Try to limit your dog’s movement, and carry them if possible (any movement can worsen the signs of shock).

What Should You Avoid Doing?

Do not attempt to take a wait and see approach or to trial medication at home. As this is a potentially life-threatening emergency, you need to seek veterinary help.

How Are Severe Allergic Reactions in Dogs Diagnosed?

Your vet will be suspicious of an allergic reaction based on your dog’s history and signs.

What Tests May a Vet Perform?

Tests are not always indicated, but your veterinarian may perform a blood pressure measurement and basic blood tests. Blood sugar, lactate and ALT (alanine transaminase) are all affected by shock.

Allergy screening tests (such as IgE blood tests or intradermal skin tests) would not be run, as results are often inaccurate during or shortly after an episode of anaphylaxis. They can be carried out a few weeks after the episode, if there is doubt over the trigger.

How Are Severe Allergic Reactions in Dogs Treated?

Timely therapy is a must, and your vet will begin treatment the moment your dog arrives at the clinic.

First Steps

Your vet will aim to stabilise your dog, which may mean providing high-rate intravenous fluids, administering oxygen, and injecting medications including adrenaline, corticosteroids, and/or antihistamines. Which drugs are used depends on how severely affected your dog is.

How Quickly Do Dogs Respond to Treatment?

Treatment is usually rapid and dramatic. We expect to see improvement within minutes, and dogs may be fully back to normal in less than an hour.

Can Severe Allergic Reactions Be Prevented in Dogs?

Most of the time, allergic reactions can be prevented by avoiding the trigger. However, not every reaction is predictable.

For example, we could not have known that a dog would react to an antibiotic or vaccination for the first time.

Get Emergency Vet Care for Your Dogs' Allergic Reactions

Contact us any time, day or night, if you are worried your dog may be experiencing anaphylaxis. As patients require immediate therapy, it is always best to err on the side of caution when it comes to allergic reactions.

Allergic Reactions in Dogs FAQs

Can Dogs Go Into Anaphylactic Shock?

While some species are much more resistant to anaphylaxis, it is something that we see in dogs.

How Fast Do Allergic Reactions Develop in Dogs?

True allergic reactions progress rapidly over seconds and minutes.

Can I Give My Dog Antihistamines at Home?

Very mild allergic reactions (such as some red skin or a few hives that are not progressing) may be managed at home with antihistamines and close monitoring. Always call your vet first to discuss the plan.

Can a Dog Fully Recover After a Severe Allergic Reaction?

Absolutely, most dogs go on to make a full and rapid recovery. The dog will likely always have allergies, which must be closely managed to prevent future episodes of anaphylaxis.