Allergic reactions can vary from mild to severe. The most severe reaction is anaphylaxis, an immediate reaction that leads to life-threatening symptoms that include vomiting, diarrhea, staggering, rapid drop in blood pressure, swelling of the larynx leading to airway obstruction, and cardiovascular collapse. Urticaria is rapid swelling and redness of the lips, around the eyes, and in the neck region that can be very itchy. Hives may also occur. Urticaria may progress to anaphylaxis.

Both anaphylaxis and urticaria are reactions that are triggered by antibodies that the immune system has made. The antibodies cause inflammatory cells like basophils and mast cells to release substances that cause the allergic reaction.

Allergic reactions may occur in animals of any age, breed, or sex. The impact on the dog may be life threatening for both urticaria and anaphylaxis. However, if treated successfully the prognosis for long-term health is good.

What to Watch For

Vomiting

Diarrhea

Staggering and weakness

Collapse

Difficulty breathing

Rapid swelling and redness around the lips, eyes and/or neck

Itching

Hives

Diagnosis

There is no diagnostic test for anaphylaxis or urticaria, but a quick physical exam is usually diagnostic of an allergic type of reaction. The cause of the reaction can sometime be much harder to determine.

Many cats do not develop swollen face and hives associated with allergic reactions. Typically, cats begin vomiting and become profoundly weak. Since the cause of the allergic reaction is not known, it is possible that an allergic reaction may not be diagnosed; there are many things that can result in sudden vomiting and collapse in a cat. Fortunately, most have similar treatments.

If your cat has repeated episodes of allergic reactions, it is important to try to find the cause of the reaction. This way, you may be able to prevent future exposures.

Treatment

Anaphylaxis is an extreme emergency. Your veterinarian will begin immediate emergency life support including establishing an open airway, administering oxygen, intravenous fluids to increase blood pressure, and drugs such as epinephrine and corticosteroids. Animals that survive the first few minutes usually return to normal health. Anaphylaxis usually occurs soon after exposure to the allergic substance.

Urticaria also occurs soon after exposure. Your veterinarian may recommend immediate examination and treatment and an oral antihistamine such as diphenhydramine (Benadryl) to initiate treatment. Urticaria is usually treated successfully with injectable corticosteroids like dexamethasone or prednisolone. Antihistamines do little to help with acute allergic reactions but may be given by injection to help prevent recurrence of symptoms after the steroids wear off.

Home Care and Prevention

Any time your cat suddenly begins to vomit and becomes profoundly weak, examination by a veterinarian is recommended. Severe allergic reactions are rare. Since the cause of the allergic reaction is unknown, prevention is difficult. Early recognition and treatment is vital to a successful outcome.