5 Signs Your Pet Is Having an Allergic Reaction

Published Jan. 24, 2018

Allergic reactions are something we have in common with our pets. Anaphylaxis, a severe and potentially life-threatening reaction often seen in people following exposure to things such as shellfish, nuts, and insect stings, can also affect dogs and cats.

Both people and pets are susceptible to numerous allergens such as insect bites or stings, drugs (like medications and vaccines), foods, and environmental substances (like mold, pollen, grass, and house dust mites).

Allergic reactions have both a multitude of causes and manifestations. It is important for pet owners to be familiar with the various symptoms of allergic reactions so that medical attention can be administered in a timely manner.

Here are 5 signs your pet is having an allergic reaction and how to treat them:


Itchiness is one of the most universal manifestations of allergies in pets.

Itchiness can be either localized or generalized. Some of the common areas that are affected include the:

  • Limbs

  • Face

  • Ears

  • Armpits

  • Hindquarters

Pets with allergies are often observed biting, licking, or scratching at these sites, resulting in inflamed skin and hair loss.

Dogs and cats suffering from severe allergies might traumatize their skin, resulting in open sores and infection.

Seeking veterinary attention at the onset of itchiness is important to keep pets comfortable and prevent skin infections.

Facial Swelling

Seeing a pet with a swollen face causes both alarm and distress for owners.

Puffiness can occur on the muzzle, ears, and around the eyes. A change in a pet’s appearance is more dramatic and noticeable in pets with short hair coats.

Areas that become swollen as a result of an allergic reaction are also often itchy, so a pet scratching or rubbing its face will also alert owners of a problem.

Medical treatment, fortunately, provides rapid relief for pets suffering from this uncomfortable symptom.

Hives (Urticaria)

As with facial swelling, the onset of hives is more readily recognized in pets with short fur.

Owners of pets with thick or long coats may not visibly notice hives but will need to rely on their sense of touch in order to detect this symptom.

Hives manifest as raised bumps throughout the skin. They may or may not be accompanied by itchiness.

While they are not life-threatening, hives require urgent medical treatment for your pet’s comfort.

Gastrointestinal Problems

While most commonly associated with allergy-inducing foods, vomiting and diarrhea can result from any allergen.

Protein-based foods such as beef and dairy products are more likely to cause allergies in pets than grains, and pets who become allergic to a particular food ingredient may have itchiness, vomiting, and/or diarrhea.

The diagnosis of food allergies is difficult and requires a prescription diet consisting of a novel protein source (like venison, rabbit, or duck) or hydrolyzed protein, which is less likely to cause inflammation within the gastrointestinal tract.

Pets with non-seasonal itchiness along with vomiting or diarrhea should be evaluated for food allergies. Some pets with food allergies merely become itchy in the absence of gastrointestinal symptoms.

Your pet’s veterinarian can discuss protocols and tests for discerning food allergies from inhalant allergies.

Vomiting and diarrhea can also result from an anaphylactic reaction. During anaphylaxis, the immune system is activated to release many chemicals. These agents have a systemic effect on many areas of the body, including the stomach and intestinal tract.


Anaphylaxis is the most severe and serious type of allergic reaction. It can cause the body to go into shock resulting in:

  • Decreased blood pressure

  • Difficulty breathing

  • Collapse

  • Loss of control of the urinary bladder and bowels

Any allergen can cause anaphylaxis in pets.

One of the more common causes of anaphylaxis in dogs and cats is vaccines. Pets that receive vaccines should be monitored closely and not left unattended immediately after the injection has been administered.

Following vaccination, monitor your pet for:

  • Lethargy 

  • Weakness

  • Pale gums

  • Labored breathing

  • Vomiting

If anaphylaxis occurs, symptoms are seen within a few minutes. If not treated promptly, anaphylaxis can be fatal. It is important for pets to have any anaphylactic reaction documented in their medical record.

In the future, vaccinations should be given with precautions such as the administration of reaction mitigating medications ahead of time and close supervision afterward.

Treatment of Allergic Reactions

The management of allergic reactions is dependent upon the severity of symptoms.

If your pet is stung by an insect, carefully remove the stinger if possible and apply ice or a cool compress to the area. Some pets may only experience pain at the site of the bite. Always monitor your pet for the development of hives, facial swelling, or signs of shock, and seek immediate veterinary care if problems arise.

Immediate Treatment Is Required

Pets suffering from anaphylactic reactions require immediate care. Treatments may include:

  • Injectable steroids

  • Epinephrine

  • Intravenous fluids

  • Antihistamines

Intubation to maintain an open airway and oxygen therapy are often necessary for pets experiencing difficulty breathing.

Hospitalization and close monitoring are very important following a severe allergic reaction.


Medications such as antihistamines and steroids are commonly used to treat allergy symptoms. Although common, over-the-counter antihistamines (e.g. Benadryl) are used in both people and pets, never administer medications to your dog or cat without consulting a veterinarian.


Avoidance of known allergens is the safest way to keep pets happy and healthy.

Unfortunately, prevention is not always possible. If you suspect your pet is having an allergic reaction, seek veterinary care as soon as possible.

Featured Image: iStock.com/humonia

Mindy A. Cohan, VMD


Mindy A. Cohan, VMD


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