Urticaria in Dogs

Urticaria, also known as hives or nettle rash, is a skin condition that arises from the immune system's reaction to an allergen or chemical. The reaction causes a release of histamine that results in inflammation of body tissue, hives and irritation of the skin. Urticaria in dogs is characterized by hives or wheals that arise on the surface of the skin. Within the skin are edemas, or abnormal accumulations of fluid, that form the wheals on the surface.

Symptoms and Associated Disorders of Urticaria

Dogs with urticaria will develop wheals within minutes or hours of exposure to the allergen or chemical. Wheals will appear slightly raised and can be rounded or flat on the top. Discoloration can be red or pale when compared to the surrounding unaffected skin. Wheals vary in size from ½ of an inch to about 2 inches in diameter and when large may be depressed in the center. Pruritus, or intense itching, may or may not be present. In most cases, a number of wheals will develop on the skin of the back, neck, sides, limbs or eyelids. Wheals that appear on oral, rectal or genital regions may be indicative of a more serious case, particularly if they are preceded by other symptoms such as:

  • Fever
  • Anorexia
  • Lethargy

Although rare, urticaria can be related to a potentially life threatening reaction. A dog may experience anaphylaxis, or anaphylactic shock, as an immediate and serious hypersensitivity to a medication or allergen. Anaphylaxis is an emergency and can result in coma or death if not treated by a veterinarian immediately. Dogs that go into anaphylactic shock may experience symptoms of skin irritation with diarrhea, vomiting or difficulty breathing. Angioedema, a variation of urticaria, can also cause breathing complications if the tissue swelling occurs in the respiratory passages.

Causes of Urticaria in Dogs

Urticaria can be caused by exposure to any allergen or chemical that may provoke a reaction from the immune system. Common causes include:

  • Nettle stings
  • medications (urticaria medicamentosa)
  • Chemicals (such as turpentine or crude oil)
  • Intestinal parasites
  • Inhaled or ingested allergens
  • Milk retention (during estrus)

Heat reflex urticaria, or cholinergic pruritus, is an uncommon condition that can occur when a dog's sweat glands release sweat and acetylcholine. Papular urticaria is caused by an allergic reaction to the stings or bites of insects. Dogs with papular urticaria will have hard skin lesions that appear red or brown.

Other factors may not cause urticaria, but they can instigate or exacerbate symptoms in an existent case. These factors include stress, illness, heat, exercise or prolonged exposure to sunlight. Other diseases or hereditary conditions can also be contributing factors to the onset of symptoms of urticaria.

Treatment of Acute and Chronic Urticaria

Most cases of urticaria arise quickly, and will then disappear within a few hours, with symptoms going away on their own. In these acute cases, localized treatment of the wheals is not necessary and antihistamines may even induce the urticaria. Adrenocorticosteroids may be prescribed for more serious cases, to quickly alleviate inflammation and provide relief for cases with pruritis.

Chronic urticaria may occur if a dog is continuously exposed to an allergen in the environment. Symptoms will be recurring and antihistamines may be recommended for chronic cases, until the allergen can be determined and removed from the environment.