Let’s talk about the majority (85%) of my patients with allergic skin disease who are reacting to environmental allergens. Commonly used terms for this type of allergic dermatitis are atopic dermatitis (AD) or atopy. Pets and people with atopy inherit the predisposition to become allergic, and then become allergic to various environmental proteins called antigens or allergens, based upon exposure patterns. For example, we are more likely to become allergic to things that we are exposed to cyclically, such as seasonal pollens, rather than continuously. Very high exposure levels can also make us more likely to react to some allergens, such as dust mites, and once allergic, even minute exposure can lead to allergic reactions.
Some patients have clinical signs (the term used for symptoms in animals) that are seasonal or intermittent. There are many things in our environment that lead to either predictable patterns or random flares in clinical signs, such as grasses, weeds, trees, and molds. But many patients are affected all year long, due to things that are ubiquitous around us, such as house dust mites, cotton and wool fibers, even our other pets or ourselves. OH, MY! It is like each allergic pet has a bucket inside them that holds all the allergens they collect. Each pet’s bucket is a different size, and when the bucket overflows, clinical signs start. So we can imagine how the bucket ebbs and overflows as different allergens are removed from or added to the bucket. Such is the often unpredictable world of allergies.
One of the important, inherited factors in atopic dermatitis is the presence of multiple defects in the skin barrier. This allows allergens to invade the skin surface where they start the allergic reaction. It also allows surface bacteria and yeast to cause infections. Thus, restoring normal barrier function can play an important role in treating pets with atopic dermatitis.
Although the dermatological signs of environmental allergies are indistinguishable from those of food allergy (see previous blog for discussion of clinical signs of allergic dermatitis), there are a few other clinical signs that I see in association with environmental allergies, but not with food allergies. I most commonly see ocular signs, such as red, itchy, weepy eyes. Uncommonly, my patients present with respiratory signs such as a runny nose, cough or sneeze.