How do you diagnose dog allergies?
Most dogs with allergies are diagnosed on the basis of their history and their physical examination. To determine their specific allergies, skin testing and/or blood testing may be required.
The first step that most veterinarians recommend when examining a dog with suspected allergies is to rule out other causes of itching such as skin parasites (demodectic or sarcoptic mange) or fungal infections (such as ringworm, also called dermatophytosis). Diagnostic tests may include fungal cultures or skin scrapings to look for the parasites.
How can I tell what my dog is allergic to?
It can be very difficult to tell what a dog is allergic to. The best way is for skin testing or blood testing.
Below are some guidelines to help you understand more about the most common dog allergies and what might be affecting your dog.
- Flea allergy dermatitis is the most common allergic skin disease seen in the United States. Dogs with flea allergies tend to chew and scratch at their back ends, so lesions are typically seen over the rump, on the belly, and between the hind legs. This difference helps differentiate this disease from atopy. It is possible, however, to see atopy and flea allergy in the same animal. Like food allergies, atopy is sometimes responsive to corticosteroid (hormone) treatment.
- Dogs with allergies secondary to atopy usually begin to develop symptoms relatively early in life, often by one year of age. Symptoms are usually seasonal at first, with most dogs showing clinical signs in the summer months when airborne allergens (such as plant pollens) are present in higher concentrations. As atopic dogs age, they tend to become allergic to more substances. Eventually, their itchiness can occur year-round.
- Food allergies in dogs commonly cause a pruritic skin condition. As with atopy, dogs with food allergies often chew their feet, rub their faces, and scratch their ears. Thus, the symptoms of food allergy are virtually indistinguishable from those of atopy. One important difference to remember is that atopy symptoms usually begin between one and four years of age whereas food allergies can begin at any age. A dog with an onset of symptoms who is less than eight months of age or over six years of age is unlikely to have atopy. Also, atopy is usually well controlled by treatment with corticosteroids such as prednisone. Food allergies are variably responsive to prednisone; only about 50 percent of affected dogs will see improvement after treatment.
How are dog allergies treated? Treatment for skin allergies in dogs
Treatment for skin allergies in dogs may include medications that can alleviate symptoms, but they do not treat the underlying cause of the allergy. Caring for dogs with allergies is extremely frustrating; allergic reaction is a life-long disease with no easy “cure.”
Immunotherapy (shots that work by modifying your dog's immune response to allergens) is considered the best treatment for moderate to severe or long-standing cases of allergy. However, the recommendations for your allergic dog will depend on your dog’s underlying symptoms (such as healing skin infections, irritation caused by itching, and ear infections that require medication) as well as the treatment for the potential causes of allergic reactions such as fleas
Your veterinarian may recommend the following for dog allergy care:
- Flea control medications (for dogs with flea allergies)
- Limited ingredient diets (for dogs with possible food allergies or multiple allergies)
- Antihistamines including Benadryl, Chlortrimeton, and Zyrtec; there are many on the market, and some dogs will respond to one antihistamine but not another so many pet owners try a variety before concluding they don’t work.
- Fatty acid supplements to relieve itchiness by modulating the immune response; certain fatty acids such as eicosapentanoic acid (found in fish oil) help change the chemical composition of cell membranes and, ultimately, the types of chemical mediators produced during the allergic response, which results in a milder response from the body. Like antihistamines, these products are not helpful in all affected animals, but they are very safe. Some dogs that do not respond well to antihistamines may respond to a combination of antihistamines and fatty acids.
- Antibiotics to treat secondary bacterial infection of the skin (called pyoderma) or ear infections; yeast infections of the skin and ear also have to be treated occasionally.
- Topical therapy for skin wounds (often a spray of a solution of an antibiotic and steroid)
- Soothing and therapeutic shampoos; topical therapy may be very helpful in managing itchiness caused by allergies. Shampoos that contain colloidal oatmeal are soothing and moisturizing and can be used frequently without drying the skin. Some oatmeal-based shampoos contain topical anesthetics or corticosteroids that are very safe and help further reduce itchiness.
- Corticosteroids (cortisone-like drugs such as prednisone); these are very effective at reducing the symptoms of allergies, but they have many potential side effects that limit their long-term use. This class of drugs is very effective in allergic dogs; unfortunately, these drugs also have many potential adverse effects that restrict their long-term use. Examples of the adverse effects of corticosteroids include increased water consumption and urinations, increased appetite and food intake leading to obesity, suppression of the immune system leading potentially to secondary infections, irritation of the stomach, alterations in liver function tests, and suppression of normal adrenal gland activity. Short-acting, orally-administered corticosteroids are safer than long-acting injectable corticosteroids because the former can be cleared rapidly from the animal's body in the event of adverse effects. Any dog that can be helped by long-acting injectable corticosteroids can be relieved just as effectively and with less risk by the use of short-acting orally-administered corticosteroids.
- Immunotherapy (hyposensitization, desensitization, allergy shots); this is theoretically the ideal form of treatment for dog allergy care and is recommended for dogs that cannot be managed safely and effectively with symptomatic therapy. The exact mechanism by which immunotherapy works is not well understood, but the goal is to induce tolerance of the immune system to allergens to which the animal is sensitive. This technique is effective in 60 to 80 percent of atopic dogs. An extract of the allergens selected by allergy testing is prepared. Initially, a small amount is injected frequently (every 1 to 2 days), and the dosage is gradually increased. Due to the frequency of injections, your veterinarian may show you how to administer the injections at home. Once the cumulative dose reaches a certain level, the injection interval is slowly increased until injections are given every 2 to 3 weeks. The interval then may be maintained for a relatively long period of time. Improvement is gradual, and your dog may not benefit markedly for the first 3 to 6 months of immunotherapy. Antihistamines, fatty acid supplements, and soothing shampoos may be used while immunologic tolerance develops.
- Use of an immunomodulator drug called cyclosporine A (Atopica®, Novartis); cyclosporine has properties that fight against inflammation and itching. It is generally started daily and often decreased to every other day or every third or fourth day as clinical signs improve. It may take four to eight weeks to see improvement.
- A newer therapy called Oclacitinib (Apoquel); this drug has been very effective in controlling itching in dogs with allergies. It uniquely targets cytokines that are involved in the itching process. The onset of relief can be as early as 4 hours, and treatment controls the itch within 24 hours. Many veterinarians like this drug because it controls itching without the side effects of steroids.