Hives are an allergic reaction characterized by the sudden appearance of raised, circular, itchy wheals on the skin of the face and elsewhere. The hair sticks out in little patches. Frequently, the eyelids will also swell. Hives generally appear within 30 minutes of exposure and disappear within 24 hours.
Insect bites are a common cause of hives. Hives can occur after a vaccination. Penicillin, tetracycline, and other antibiotics can produce hives. Topical insecticides and soaps are other causes. Hives that come and go usually are caused by an allergen in the dog’s environment.
Treatment: When possible, identify the allergen and prevent further exposure. When a food allergy is suspected, modify the dog’s diet (see Food Allergy). In the case of an acute reaction, you can give a dose of Milk of Magnesia to speed removal of the food from the intestinal tract.
When hives appear shortly after a shampoo or application of a topical insecticide, bathe the dog and rinse thoroughly to remove the chemical from the dog’s coat and skin.
Hives usually respond well to an antihistamine such as Benadryl. Cortisone may be needed to control a severe case. Consult your veterinarian.