Severe allergic reactions in pets

isolated pets


  • Pets can have allergic reactions just like people.
  • Common triggers include insect stings, plants and medications (including vaccinations).
  • Symptoms of an allergic reaction (listed below) can start suddenly and without warning.
  • Severe allergic reactions can be life threatening.
  • Get vet help ASAP if you think your pet is having a severe allergic reaction.

General information and causes

Pets can have allergic reactions just like people. Allergic reactions happen when the body overreacts to something. It’s possible for a pet to be allergic to almost anything but the most common triggers include:

  • Medicines (such as vaccines, flea medicines and antibiotics)
  • Insect stings and bites
  • Certain chemicals
  • Certain foods.

The first allergic reaction to a substance is usually quite mild, but each reaction after that is likely to be worse. However, occasionally a first reaction is severe and happens without warning.

dog allergic reaction after bee sting

This dog is having an allergic reaction after a bee sting.

First aid for a severe allergic reaction

Step one: Check your pet

Symptoms vary depending on what your dog has reacted to and how severe their reaction is.

Signs of a severe allergic reaction (anaphylaxis) include:

  • Breathing difficulties (if your pet stops breathing, they may need CPR)
  • Rapid swelling (often of the lips or eyes)
  • Cold ears, legs and feet
  • Collapse/ fainting
  • Coma or death.

Other, signs of a milder allergic reaction include:

  • A skin rash/ bumps
  • Swelling around other parts the body
  • Sickness or diarrhoea
  • Drooling.

Step two: Take your pet to your vet

  • Anaphylaxis is the same kind of life-threatening reaction that some humans get with peanut allergies, it’s an emergency that should be treated immediately.
  • If your pet has trouble breathing or their face is swelling up quickly go to your vets ASAP - if possible, phone on the way to check they are ready for your pet to arrive.
  • If you see mild signs, call your vet for advice. They may need medications to help stop the reaction getting worse and to keep them comfortable.


Treatment for an allergic reaction depends on how severe the reaction is. If your pet has a mild reaction, they’re likely to be given medication to prevent it getting worse and you will be asked to monitor them at home.

If your pet has a more severe reaction, it’s likely they’ll be admitted into the veterinary hospital for intensive treatment. Treatment for a severe reaction is likely to include a fluid drip, medication to reduce their reaction and in some severe cases, a tube placed into their airways to help them breathe.

Published: March 2020

PetWise Pet Health Hub – brought to you thanks to support from players of People’s Postcode Lottery 

Written by vets and vet nurses. This advice is for UK pets only.

Illustrations by Samantha Elmhurst