Allergic reactions for dogs often appear on the skin in the form of redness, swelling, and itching. Urticaria, known more commonly as hives, is another common skin reaction to allergens. Although hives are not generally life-threatening, they can develop into more serious problems. These small raised wheals are extremely itchy, and if your dog scratches at them, they may become even more inflamed or even rupture which can lead to dangerous skin infections. Swelling that occurs in the throat and nasal passages can also make breathing difficult, if not impossible.

Urticaria, known more commonly as hives, is a common skin reaction to allergens that produces red, raised bumps that cause intense itching.

Not every bump or inflammation on a dog can be considered hives. Hives generally develop within approximately twenty minutes after exposure to the allergen. They are cutaneous wheals, meaning that they are bumps that appear on the skin itself rather than the fatty layer under the skin. They are round, raised bumps that are between one to five centimeters in diameter, but severe hives can occasionally converge to create a larger mass.

Hives are not the only type of bumps that can be indicative of an allergic reaction: 

Although any allergy can result in hives, certain types of allergens are prone to causing them. The most common triggers for hives can include:

Hives have a fairly distinctive raised appearance and can often be diagnosed visually. The primary diagnostics are not focused on the symptom of hives, but rather on the cause of the hives themselves. Allergies are the most frequent cause of hives, but there are many types of allergies, so the emphasis is placed on determining the allergen that is causing the reaction. The veterinarian is likely to request a biochemistry profile and a complete blood count which may expose a type of white blood cell that would indicate an allergic reaction called eosinophils.

Skin scrapings will often be taken from any areas that are affected by the hives or by other types of rash, for use in the microscopic examination of the skin cells to look for issues like signs of disease, mites, or yeast infections. This type of evaluation is called a cutaneous cytology. 

In some cases, small amounts of the suspected allergen or allergens are injected under the skin to confirm that suspicion (intradermal testing). In the event that the allergy is a food related allergy, dietary trials are often the best method to uncover which ingredient the patient is reacting to.

If your dog has developed hives due to allergy, your veterinarian will give you instructions on how to ease the itching and swelling. Quite often urticaria disappears spontaneously, but in cases where it persists, antihistamines like Benadryl or Zyrtec are often the first line of defense when it comes to treatments given to combat allergic reactions if medication is required. However, many natural remedies may ease the itching of urticaria. Colloidal oatmeal (oatmeal ground into flour) is a safe and inexpensive treatment which can be found in many pantries, and essential oils like lavender and chamomile can help relieve the itching and pain associated with hives.

Your dog’s doctor should also be consulted before using any over-the-counter medications, as the dosage for canines is quite a bit different than the dosage for humans, and it can vary based not only on your dog’s weight, but also based on their physical condition and other medications they may be taking. Antihistamines are only effectual in around 20% - 30% of dogs who are allergic. In severe or chronic episodes, corticosteroids may be required.

As allergic reactions tend to get more aggressive over time, it may be recommended that you get a prescription for an epi-pen if your dog has had a moderate to severe allergic reaction involving hives or angioedema. This device has a properly measured dose of epinephrine for your dog. Canines over 45 pounds are generally prescribed a regular adult EpiPen, canines between 20-45 pounds will use the EpiPenJr, and animals smaller than 20 pounds will usually be given a syringe with the right sized dose for their size. Use of an EpiPen should be followed by a trip to the emergency room, even if your dog appears fully recovered. Epinephrine is a short-acting drug, and the allergic reaction may resume without proper medical treatment.