Atopy, or allergic dermatitis (commonly – “grass allergies”), occurs when an individual develops allergic symptoms as a result of exposure to an airborne allergen. In the case of atopy, the allergen is typically inhaled or absorbed thru the skin. Common allergens involved in atopic dermatitis include pollens, grasses, molds, dust and dander. In humans, symptoms of atopy include sneezing, itchy eyes or asthma (what we think of as hay fever). In pets, symptoms of atopy include redness and itching in the skin around the face, ears, paws, armpit, groin and rectum that leads to chewing, biting and scratching these areas of the body. Similar patterns of itchiness can develop in cases of food allergy. Flea allergy dermatitis typically involves itchiness that develops over the trunk on the back half of the body.
Based on symptoms alone, it can be difficult to distinguish the cause of your pet’s itchiness. Along with food allergy, there can be other causes of itchy skin, such as parasites or infections caused by bacteria, yeast or another fungus. It is important for your veterinarian to perform a complete physical exam and obtain a thorough history when treating itchy skin. There are some characteristics of atopy that may help distinguish it from other causes of itchy skin. Symptoms of atopy typically develop between the ages of 1 and 3 years. In contrast, food allergy symptoms often develop later, between the ages of 5 or 6 years in dogs. Atopy often starts as seasonal itchiness but eventually may persist year-round. Food allergy symptoms are non-seasonal. Symptoms of atopy are typically very responsive to corticosteroid (cortisone-type) treatments. Itchy skin due to food allergy or infection is variably responsive to steroid therapy.
Examination and history alone may not be sufficient to determine if your pet is suffering from atopic dermatitis. Your veterinarian may recommend performing some diagnostics to rule out other causes of itchy skin, such as a skin cytology (to look for bacteria or yeast), skin scraping (for mite identification), or cultures (for fungal or other infectious agents). Once other types of infections are ruled out, testing to diagnose atopy may be recommended. Intradermal skin testing (injecting small volumes of allergen under the skin and monitoring the skin reaction) or blood testing (measuring levels of antibodies to specific allergens) can be performed.
If either intradermal skin testing or blood testing for atopy has been performed and specific allergens have been identified, immunotherapy may be recommended. This involves administering an “allergy vaccine” either orally or by injection to desensitize your pet to the allergen. Approximately 60-80% of pets will improve within 6 months of starting therapy. Allergy vaccine therapy is typically life-long once started. Avoidance (if possible) is another therapeutic option. Exposure to house dust mites and molds can sometimes be minimized with identification and reduction of indoor sources. Exposure to pollens can be reduced by wiping down with moist cloths after going outside or frequent bathing.
When the specific allergen(s) has not been identified, management of atopy typically involves administration of oral medications that help reduce the body’s inflammatory response to allergens and topical treatments to prevent secondary skin infections. Oral antihistamines can safely be given long-term with very few side effects. However, antihistamines only work in about 20% of atopic pets. Concurrent use of oral fatty acid supplements may help improve response to antihistamines. Fatty acids are anti-inflammatory but also have a synergistic effect when used with antihistamines. As mentioned above, oral steroids are very effective at controlling the symptoms of atopy. However, long-term steroid use has many potential adverse side effects. Therefore, steroid therapy is reserved for short-term seasonal control or in patients where other therapy is not feasible or effective. Cyclosporine (Atopica) is an oral immunosuppressive agent that can be used to treat the symptoms of atopy. Atopica helps approximately 60% of patients with atopy. Side effects associated with long-term use are not completely known.
Topical treatment can help to reduce itchiness and prevent or treat secondary skin infections. Bathing with a hypoallergenic, moisturizing shampoo and rinse can help to reduce topical allergen exposure. Topical steroids can be used if the symptoms are localized to a small area of skin, eyes or ears. Overuse of topical steroids can lead to side effects associated with oral or systemic use of steroids. Topical tacrolimus, a topical immunosuppressive, is another option for control of localized itchiness. Medicated shampoos are sometimes prescribed to reduce secondary infections that occur with chronic allergic dermatitis. Reducing bacteria and yeast on the skin further reduces itchiness.
Itchy skin in pets is very common but the cause is not always obvious without a thorough examination, history and possibly some testing. It may be necessary to perform testing and trials of therapy to discover the cause of the skin disease and what best controls your pet’s specific skin condition. Treating atopy can require a multi-modal approach of oral medication, topical treatments and possibly desensitization therapy. We at Dupont Veterinary Clinic strive to provide your pet with the best care possible and hope that we can make you and your pet as happy and comfortable as possible!