Q. I have been allergic to animal dander (dogs, cats, horses - you name it) my whole life, but as some cruel twist of fate, I am absolutely crazy about animals. Despite the itchy, runny nose, swollen eyes and mild asthma, I dutifully go to walk dogs at the SPCA International for about 8 hours every weekend (in fact, since I walk them outside, I rarely have an allergic reaction). There is nothing that gives me greater joy than to see a dog leaping and running and wagging its tail. Even as a child, when my mother told me to go play with my friends, I headed straight for the collies next door. On the other hand, every time we went to visit my cat-crazy aunt, I had to make a decision between spending the entire visit outside in the snow or passed out from antihistamines under the coats in the spare room. Fortunately, non-sedating antihistamines came along - and these seem to relieve all of my symptoms. Now that I'm all grown up and have given up my dreams of becoming a veterinarian, I really think it's only fair I should be able to have a dog. Is there any harm in using an antihistamine every day? And will it continue to work with constant exposure to an allergen (in this case, dog)?
A. The use of long-term antihistamines is not a major concern in terms of drug safety. If you tolerate it now, you should continue to tolerate it. With the older, first generation antihistamines, e.g., diphenhydramine, there can be some loss of effectiveness (sub-sensitivity or tolerance) and while this may also apply to the newer, second generation, non-sedating antihistamines, the evidence is not conclusive.A larger concern focuses in two areas. When one lives with an animal there will be more intense exposure, and you may develop symptoms that are not adequately controlled with any oral antihistamine. In fact, most severe animal-allergic people often require more than one daily medication, and this usually includes a nasal steroid and an eye drop. And while use of these medications on a daily basis is quite safe, we do not have data on safety for long-term, e.g., 20+ years, of daily use.On the other hand, there are times that living with an animal actually slightly reduces the allergenicity so that there are fewer symptoms. Unfortunately, we cannot predict which of these scenarios will play out for you, or any other individual to a specific dog. Yes, you CAN be more allergic to one dog than another dog. A brief exposure to a specific dog may not predict how you will react to that dog a few weeks later. The other concern is that by allowing your nose to tolerate the dog (by taking an antihistamine), you are inhaling more dog dander and have the possibility of developing allergic asthma, as the lungs have a lining that is very similar to that of the upper airway. While we see this progression from nasal allergies to asthma more commonly in children, it does occur in adults.If you are interested in having a dog, I would recommend that you consult an allergist and consider starting on a course of allergen immunotherapy (allergy injections) to reduce your sensitivity to dog dander. This is the only form of preventative and long-term control medical treatment available. In addition, a dog-allergen-minimizing home environment would be helpful. Presuming you would have an inside dog, measures could include hard surface flooring, leather furniture, a bedroom that is off-limits to the dog, and use of HEPA devices (vacuums and air cleaners).