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).

Q. Are there any breeds or types of dogs that won’t trigger allergies in dog-allergic people?

A. The reason some people are allergic to dogs is because their immune system reacts to specific proteins (“allergens”) in the dog’s dander, saliva and fur. Not all dog-allergic people react to the same dog allergens, and not all dogs produce or shed the same amount of all dog allergens. So it is theoretically possible that some dogs could be better tolerated than others.

In the past, some have thought that breeds known to shed less fur ought to shed fewer allergens. These so-called "hypoallergenic" dog breeds include as Samoyeds, Portuguese water dogs, Afghan hound poodles, Airedale terriers and Malteses. However, homes containing these theoretically less allergenic breeds may have the same dog allergen contain as houses where fuzzier breeds curl up at the foot of the bed, according to a recent study of residences around Detroit, Michigan. The researchers from the Henry Ford Health System in Detroit in conjunction with the Georgia Health Sciences University examined the content of homes for the common dog allergen Canis familiaris 1 (Can f 1) and found detectable levels in 94% of the 173 homes they tested. In fact, the levels of common dog allergen, Can f 1, were not statistically different between houses inhabited by "hypoallergenic dogs" and those harboring other breeds!1

Thus, while it appears there are differences in the amount of allergen shed by individual dogs, there are no clear and consistent differences between breeds, even those that shed less fur or are thought to be less allergenic. So there is no guarantee that picking a dog of a particular breed is a good way to reduce the amount of allergen in your home or to avoid symptoms.

Perhaps someday we will be able to routinely determine which allergens an individual person reacts to, and measure the levels of those allergens shed by individual dogs. Perhaps choosing a pet based on this strategy would lead to fewer symptoms. For now, that strategy is unproven and those tests are not readily available. And there is no guarantee that, over time, you won’t develop an allergy to one of the other dog allergens, or that the dog won’t produce higher levels of those allergens later in its life.

In the meanwhile, your allergist is able to evaluate your dog-related symptoms and prescribe the best medicines to prevent or treat those symptoms. In addition, allergen immunotherapy (“allergy shots”) can expose you to dog allergens in such a way that you actually become less allergic to dogs over time. Unfortunately, for some people, the best medical advice is to avoid exposure to dogs that cause or exacerbate your symptoms. Don’t be looking for love in all the wrong places!

1 Nicholas et al, "Dog allergen levels in homes with hypoallergenic compared with nonhypoallergenic dogs", American Journal of Rhinology & Allergy. 2011;25(4):252-6.

Q. After a recent trip to the local animal shelter, my children want to adopt a dog or cat. I have always considered myself to be a very allergic person and feel that my allergies will become worse if we bring an animal into our home. A coworker of my husband told him there are dogs that are non-allergenic or hypoallergenic, allowing an allergy sufferer to have a pet in their home without having symptoms. I want to know if this is true and which type of dog would be considered non-allergenic. I would also like to know if there are certain breeds of cats that fit into this category?

A. Unfortunately there are no "non-allergenic" cat or dog breeds! All of these have some level of allergen. Further, the allergic potential of dogs or cats is not affected by the length of their fur. This is a common myth! The protein found in the animals' saliva, dander and urine is what causes allergies. Almost 10 million pet owners - including children - are allergic to their animals. The fur of a dog or cat can, however, collect additional allergens such as pollen and mold spores. Cats seem to be more allergenic than dogs. Almost all already-allergic people exposed to cats on a regular basis will become allergic to them as well.

If you plan to introduce a pet into your home, have an evaluation by a board certified allergist incluing skin testing. In doing so, you will know for certain to what you are allergic. If found allergic to dogs or cats, consider immunotherapy (allergy shots). These shots will eventually, over a period of time, desensitize you to these animals, so that you may one day be able to have a family pet without compromising your health or well being.

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