By Jean Hofve, DVM
Interested in learning more? Check out the other two articles in the series!
Part 1: Overview of Allergies
Part 3: Food Allergies
Atopy is an exaggerated Type I ("immediate") hypersensitivity reaction. This type of reaction usually occurs within 30 minutes of contact with the allergen, but always within 12 hours. All atopic disorders are allergies, but not all allergies are atopic. Flea bite and food allergies are examples of non-atopic allergic disorders. Pets may have more than one type of allergy; in fact, pets who develop one allergy are more prone to develop others. Because purebred dogs are more often affected, genetics also plays a role.
Atopy specifically refers to allergies to inhaled particles, such as dust, pollen, or mold. In humans, “hay fever” is one of the most common atopic reactions, but pets very rarely get respiratory symptoms. Instead, they usually manifest the reaction in their skin as dermatitis (inflammation of the skin). Skin symptoms of atopy (also called atopic dermatitis or allergic skin disease) include itching (which can be intense), redness, scaly skin/dandruff, rashes, hair loss, and ear infections.
Although either food allergies or atopy may cause symptoms in the skin, digestive system, and/or respiratory systems, one clue to atopy is that it is frequently seasonal, with the worst symptoms occuring in the spring and summer.
The first step in diagnosing atopy is to rule out other causes of those symptoms, such as ringworm or other fungal infection, mites, fleas, and disorders of the skin glands. This may involve skin scraping, fungal culture, and other tests.
Diagnosing allergies of any kind is a challenge, but atopy is the most difficult. There are hundreds of types of pollen and mold, as well as multiple components of dust including dust mites, skin cells, and other stray proteins. For instance, a dog may be allergic to a cat in the same household.
Figuring out which allergens are causing problems can be expensive and complicated. While atopy lesions do typically occur in certain locations of the body, food and fleabite allergies may turn up in the exact same areas; so location of skin lesions is not a reliable guide to the type of allergen involved.
A common complication of atopy is secondary infections with bacteria or yeast. These infections need to be addressed at the same time as other treatment, or they will prevent healing.
Differences between dogs and cats
In dogs, the itchiest areas are usually the ears, legs, paws, tummy, and base of the tail. Secondary bacterial infections are common; they typically produce scaly, red, circular lesions. Dogs are apt to persistently lick itchy areas, which can cause moist, open lesions called “hot spots,” as well as thickening and blackening of the skin, commonly on the lower abdomen. Diagnostic tools such as blood tests and intradermal skin tests can be used to narrow the field of suspect allergens. Although they are not 100% accurate, test results may help focus allergen reduction efforts and other treatment possibilities.
In cats, a rash-like pattern called “miliary dermatitis” is the most common symptom, and most frequently occurs around the face and ears. Self-mutilation by rubbing on carpet or other rough surfaces, scratching with the hind feet, or overgrooming with the tongue may occur. Both blood and skin testing in cats is notoriously inaccurate.
There are many holistic treatment options for atopy; most can be used at the same time as conventional therapy, such as hyposensitization.
If your pet is miserably itchy, conventional treatment with a short course of antibiotics, steroids, or antihistimines may be necessary for relief while holistic treatments—which typically take a little more time—are working.