It's startling for many pet owners to learn that their furry friends also are susceptible to allergies, including hives (urticaria). Contact with plants, insect stings or certain types of food can cause a dog to break out in hives. While usually not serious and rarely lasting for more than a few days, these welts are extremely itchy, and many dogs will scratch themselves raw during an outbreak. In conjunction with this problem, many dogs also develop swelling of the face, a condition known as angiodema.

The good news is that hives aren't very common in animals. Those that are affected, however, tend to have them constantly, and it can become a challenge to identify the cause. Complicating the problem is that an animal may suddenly develop an allergy to something that it has been around its entire life without prior problems.

In pets, hives can be easy to miss, hidden as they are under the animal's fur. To check, run your hand through the pets' coat; the welts should be felt by the fingertips. If your dog has hives and any of the following symptoms, a visit to the veterinarian is in order:

Excessive scratching

Difficulty breathing

Patches of fur that appear slightly raised

Bald patches, scales or a rash

Severe dandruff or dry skin

Greasy or smelly fur, even after a bath

A severe sunburn

A significant change in skin color or skin that seems "loose"

The skin of the animal's lips, abdomen or rectal area is yellow

There are red or purple dots or splotches on the skin

Sores on the skin that won't heal

Most cases of hives are treated with antihistamines. Severe cases may also require steroids. When the allergy is severe enough to affect a dog's breathing, epinephrine also may be required to open up the dog's airway.

Keeping your dog away from the thing he's allergic to is the only sure way to prevent outbreaks. If your dog has had a past severe reaction, such as anaphylaxis (precursor to the potentially fatal anaphylactic shock), it's critical that you identify the allergen and keep the dog away from it. If your dog has ever reacted to a vaccine, your vet needs to know, so it can be included in the animal's chart and proper precautions taken. Dogs who are allergic to a vaccine can take one safely if the veterinarian administers an antihistamine shot prior to the vaccination, and the dog is monitored for a period of time afterward.

If your pet has severe allergies but you and your veterinarian haven't been able to determine the cause, you may be prescribed an "epi-pen." This is a special syringe and needle containing a single dose of epinephrine. This can be administered to a dog having a severe reaction (including difficulty breathing), giving you time to seek emergency veterinary help. If you're prescribed one of these pens for your allergic dog, be sure to take it along on any hikes or road trips.