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Common Allergic Reactions in Dogs

Like their pet parents, dogs are susceptible to allergic reactions from many allergens. Canine symptoms can be alarming to an owner. Allergic reactions in dogs can result from bug bites, bee stings, chemicals, medication, vaccinations, shampoos, pollen, molds, and countless other irritants. Knowing what to look for can help an owner know when to contact a veterinarian and if the situation is an emergency.

A veterinarian will examine a dog with a suspected allergic reaction and attempt to determine an inciting cause and course of treatment. Treatment can include injections, pills, and sometimes hospitalization. When an allergic reaction is life threatening (anaphylaxis), a veterinarian may need to use life saving measures such as assistance with breathing and intravenous medications and fluids.

The following symptoms are commonly associated with allergic reactions in dogs:


Hives, also known as urticaria, are itchy welts or bumps on the skin. Hives can occur on one area of a dogs body or all over. They can come on gradually or suddenly. Hives can go away rapidly, but can also linger and come and go for days. If hives spread or do not go away within an hour or two, it’s important to see a veterinarian. Hives can be uncomfortable, and exist as a precursor to more serious systemic symptoms.


Swelling anywhere on the face, head or neck of a dog can be part of an allergic reaction. Also known as angioedema, in extreme situations swelling can cause problems with breathing from pressure on the airways.

It is important to consult with a veterinarian if swelling does not rapidly decrease as allergic shock, also known as anaphylaxis, can ensue. A veterinarian will help differentiate between an allergic reaction and other conditions that cause swelling, such as infections, growths, or benign accumulations of fluid.

Itchy Skin

Sudden excessive itching and scratching of the skin may be an allergic reaction. The itchiness can be on one area of the skin or all over the body including the ears. Itchy areas tend to be red, and scratching can cause skin trauma and secondary infections. An affected dog may scratch themselves incessantly which can prevent them from eating or sleeping.

An allergic reaction to flea venom can result from one flea bite. This is called “flea allergy dermatitis.” Often fleas are not found on a dog or cat with this allergy, so it does not occur to an owner that this can be a cause.

Vomiting and/or Diarrhea

Sudden onset of vomiting or diarrhea with or without blood can be symptoms of an allergic reaction. This type of reaction can be a precursor to a severe anaphylactic reaction and therefore a visit to the veterinarian is necessary. The veterinarian will rule out other problems such as gastrointestinal parasites or dietary indiscretion so that they can treat the dog accordingly.

Trouble Breathing

Sudden trouble breathing can be a symptom of an allergic reaction. A dog with trouble breathing may have increased breathing sounds and can appear to be gasping while extending their head while showing an increased abdominal effort with breathing. A dog with trouble breathing should be examined by a veterinarian as soon as possible. A veterinarian will rule out conditions such as a respiratory infection like pneumonia or an airway obstruction from a foreign object. Radiographs can help determine a cause of trouble breathing and are commonly used to determine a course of treatment with this symptom.

Final Note

Allergic reactions in pet dogs can result from many different allergens, and frequently the culprit is not found. However, it’s important to treat a dog as soon as possible to prevent symptoms from becoming worse. An untreated allergic reaction can progress to anaphylaxis, collapse, and even death. A veterinarian will typically treat an affected dog with antihistamines, corticosteroids, and supportive care. With prompt and proper treatment, most dogs will recover without any further issues.