I recently made a bibliographic revision about the influence of aeroallergens in the course of atopic dermatitis and the progression from allergic rhinitis to asthma, and the environmental control in patients with atopic dermatitis and sensitization to dogs, and I haven’t found a clear assessment in the literature.

My patient is a 9 years old girl with moderate-severe atopic dermatitis since birth. Her mother has also atopic dermatitis and her sister 7 years older than her, had atopic dermatitis since birth until 5 years old and some asthma episodes in relation with respiratory infections and pollen exposition, besides she was allergic to egg although this was resolved at the age of 14.

My patient was breastfeeding until 6 months of age and has always lived in urban area. Her AD (atopic dermatitis) has been treated with sistemic corticoids (prednisone with reboun effect in some occasions), twice or three times in the early infancy, emollients everyday and topic corticoids and tacrolimus in the reagudization periods. The AD affects mainly to the hands, but it can be said that the distribution affects all of her body and with strong sintomatology of pruritus and skin damage.

When she was 4 years old her parents brought a dog (retriever) for her and her brother and sister, and in the next year, another dog came to the house. The dogs live and sleep inside the house, they don’t have a garden.

Last year the girl started with rhinitis and conjunctivitis and her parents took her to an allergist who made prick test with positive result for several allergens among them cat and dog dander, and an analytics with the following IgE levels in serum: total IgE:719, allergen specific IgE antibodies to dog; 5,26; Alternaria 11,4; cat 0,75; lolium >100, olivo >100; cyprus grass 0,5.

The allergist said it was NOT necessary to remove the dogs from the home, because the levels of the allergen specific IgE antibodies to dog dander were very low in comparison with lolium or olive levels. The mother’s girl is worried and doubts the decision about removing the dogs from the house. She thinks the direct contact can worsen her AD.

Do you think:
1. The contact with the dogs will make the AD worse, or if the avoidance of contact with dogs can result in marked improvement of skin lesions?

2. With respect to her polisensitization to aeroallergens, do you think the probability that this girl will develop asthma in the following years will increase if the dogs stay at home or as the allergist says, it’s more important/decisive in the course of the allergy the other aeroallergens that are responsible for her rhinitis, olive and lolium?

3. Which is more important in the progression from rhinitis to asthma: the quantitative level of allergen specific IgE antibodies in the patient or the presence of the aeroallergen in the environment? There are some articles in relation with environmental prevention in atopic eczema dermatitis syndrome and asthma and the avoidance of indoor allergens, mainly mite allergen, what about dog dander? (C. Capristo, I. Romei, A.L., Boner. Environmental Prevention in atopic eczema dermatitis syndrome (AEDS) and asthma: avoidance of indoor allergens. Allergy 2004;59 (Suppl.78): 53-60)

I suppose you understand the necessity of a right assessment in this case because of the emotional links to the pets of all the members of the family. The common sense says the right position is to remove the dogs from the house but unfortunately there is confusion surrounding the literature to support this painful decision. Thank you very much for reviewing my question. Looking forward for your response.


Thank you for your inquiry, and for the additional information.

Before I directly address your questions, it should be stated that, as a practicing allergist, I clearly understand the implications, from an emotional standpoint, of removing beloved pets from a home. Therefore, I certainly concur with the importance, as you mentioned, of a “right assessment.” However, in answering your questions, I have to offer a caveat in that, as is often the case in medicine, there is not always a “right assessment.” That is, in many instances, the best we can do is offer an opinion based upon an assessment of the literature, experience, and statistical probabilities.

In addition, in this particular case, that opinion is of course impacted by what one considers best for the patient’s physical health in relationship to what must be considered best for her emotional health, so there is simply no easy answer to all of your questions. However, I will share with you my own suggested strategy in her case.

Question 1: Can contact with the dog exacerbate the atopic dermatitis?
There is good evidence in our literature to support the contention that skin contact with allergens, including pets, can exacerbate atopic dermatitis (see abstract by Adinoff, et al. below). One can infer from this the corollary that removing the pet may have a beneficial effect on the dermatitis. However, there is a cautionary note in this regard, since evidence supporting environmental control measures to treat atopic dermatitis in general has been less than definitive. Nonetheless, in my personal experience, skin contact with pets clearly exacerbates the dermatitis in some patients, and since the patient feels that contact worsens her dermatitis, I believe that the dogs are an exacerbating factor. This should be kept in mind when one deliberates as to whether or not to request removal of the dogs from the home environment.

Question 2: What is the role of allergen exposure to dog versus pollen in terms of the risk of the development of asthma?
I cannot give you a completely validated answer to this question, but we do know that there is evidence in the literature to support an increased risk of asthma with exposure to indoor pets. Since your patient seems to have developed allergic rhinitis, according to the history, since the arrival of the dog(s), it is not unreasonable to assume that she has developed respiratory sensitivity to inhalation of dog dander. One cannot give you an accurate prediction of the risk of the development of asthma, but in general, environmental control measures are helpful in reducing allergic respiratory symptoms per se. Thus, we have a probable production of allergic respiratory tract symptoms and atopic dermatitis by exposure to the indoor dogs, and this gives an increased incentive to consider removing the pets. However, this incentive is based upon her present symptomatic state and not conclusively based on the risk of developing asthma should the dogs remain in the home. I cannot comment on the allergist’s statement that olive and lolium are more responsible for her rhinitis since I have no personal experience with aeroallergen seasons in Madrid, and since you do not mention whether her rhinitis is perennial or seasonal. But based upon my experience, I would say that all of her exposures, including the dog, are important in producing her symptoms, and that the additive level of these allergens is what is ultimately most important.

Question 3: Which is more important in the progression from rhinitis to asthma?
Unfortunately, I cannot answer your question based on any evidence in the literature. You are entering an area which is one of the most confusing in our subspecialty. I have copied a number of abstracts and references below which have made an attempt to analyze the risks involved from indoor pet exposure as far as the development of asthma. I do not believe, based upon these studies, an evidence-based answer is available. If we do not have an evidence-based answer available, I certainly would not be able to compare the risk of the level of specific IgE antibodies versus the risk of aeroallergen inhalation based on any scientifically validated evidence. However, based upon personal experience, I am certainly in agreement with your “common sense” conclusion. That is, that aeroallergen exposure would be the most important, and that the “right” strategy, based upon the physical health of the child, would be to remove the dogs from the home. This would be what I would personally suggest if your patient was in my practice, regardless of the fact that the levels of specific IgE to the dogs were lower than that to the lolium and olive. But, I would make that decision, as noted, based on experience, and without clear-cut validation based on available literature.

In summary, I assume the most important part of my answer to your inquiries is whether or not the dog should be removed from the home. As noted above, I would personally suggest this. However, also as noted, the final decision would of course be impacted by the emotional effect this might have on your patient, and I am not in a position to evaluate this aspect of the decision-making process. However, as far as her “allergies and asthma are concerned,” the right decision would be pet removal in my opinion.

Thank you again for your inquiry and we hope this information is of help to you.

Atopic dermatitis and aeroallergen contact sensitivity
Allen D. Adinoff et al
Journal of Allergy and Clinical Immunology
Volume 81, Issue 4, April 1988, Pages 736–742.
Atopic dermatitis (AD) may be worsened by ingested foods or contact with irritants. We have identified 10 patients (six male and four female subjects, aged 1 to 54 years) with AD and contact sensitivity to a variety of aeroallergens. Marked improvement in skin symptomatology was noted when these patients were removed from their usual environment. The patients had markedly positive immediate wheal-and-flare reactions to a variety of aeroallergen extracts in response to prick tests and were subsequently patch tested on uninvolved skin with aeroallergen extracts (1:20 wt/vol, 50% glycerine) that elicited positive prick tests. Patch tests were applied for 48 hours, removed, and then were interpreted 24 hours later. Fifty percent glycerine was used as a negative control. Significant delayed cutaneous responses to a variety of aeroallergens were noted: house dust mite, tree, grass and weed pollens, animal danders, and various molds. Positive delayed cutaneous responses correlated strongly with aeroallergens identified in the patient's environment and/or suspected by the patients as provocateurs of their AD. Delayed cutaneous reactions were negative to aeroallergens not historically relevant to their AD. We conclude that aeroallergen contact may play an important role in selected patients with AD. The demonstration of immediate and delayed cutaneous responses in AD suggests both IgE and cell-mediated hypersensitivity as contributory mechanisms.

Meta-analysis of determinants for pet ownership in 12 European birth cohorts on asthma and allergies: a GA2LEN initiative.
Volume 63, Issue 11, pages 1491–1498, November 200
"Background:  Studies on pet ownership as a risk or protective factor for asthma and  allergy show inconsistent results. This may be on account of insufficient adjustment of confounding factors".
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PLoS One. 2012;7(8):e43214. Epub 2012 Aug 29.
Does pet ownership in infancy lead to asthma or allergy at school age? Pooled analysis of individual participant data from 11 European birth cohorts.
Lødrup Carlsen KC, Roll S, Carlsen KH, Mowinckel P, Wijga AH, Brunekreef B, Torrent M, Roberts G, Arshad SH, Kull I, Krämer U, von Berg A, Eller E, Høst A, Kuehni C, Spycher B, Sunyer J, Chen CM, Reich A, Asarnoj A, Puig C, Herbarth O, Mahachie John JM, Van Steen K, Willich SN, Wahn U, Lau S, Keil T; GALEN WP 1.5 ‘Birth Cohorts’ working group.
Collaborators (19)
Wickman M, Hallner E, Alm J, Almqvist C, Wennergren G, Alm B, Heinrich J, Smit H, Thijs C, Mommers M, Bindslev-Jensen C, Halken S, Fantini M, Bravi F, Porta D, Forastiere F, Custovic A, Dubakiene R, Mahachie J.
Department of Paediatrics, Oslo University Hospital, Ullevål, Norway.
Objective: To examine the associations between pet keeping in early childhood and asthma and allergies in children aged 6-10 years.
Design: Pooled analysis of individual participant data of 11 prospective European birth cohorts that recruited a total of over 22,000 children in the 1990s.
Exposure Definition: Ownership of only cats, dogs, birds, rodents, or cats/dogs combined during the first 2 years of life.
Outcome Definition: Current asthma (primary outcome), allergic asthma, allergic rhinitis and allergic sensitization during 6-10 years of age.
Data Synthesis: Three-step approach: (i) Common definition of outcome and exposure variables across cohorts; (ii) calculation of adjusted effect estimates for each cohort; (iii) pooling of effect estimates by using random effects meta-analysis models.
Results: We found no association between furry and feathered pet keeping early in life and asthma in school age. For example, the odds ratio for asthma comparing cat ownership with "no pets" (10 studies, 11489 participants) was 1.00 (95% confidence interval 0.78 to 1.28) (I(2) = 9%; p = 0.36). The odds ratio for asthma comparing dog ownership with "no pets" (9 studies, 11433 participants) was 0.77 (0.58 to 1.03) (I(2) = 0%, p = 0.89). Owning both cat(s) and dog(s) compared to "no pets" resulted in an odds ratio of 1.04 (0.59 to 1.84) (I(2) = 33%, p = 0.18). Similarly, for allergic asthma and for allergic rhinitis we did not find associations regarding any type of pet ownership early in life. However, we found some evidence for an association between ownership of furry pets during the first 2 years of life and reduced likelihood of becoming sensitized to aero-allergens.
Conclusions: Pet ownership in early life did not appear to either increase or reduce the risk of asthma or allergic rhinitis symptoms in children aged 6-10. Advice from health care practitioners to avoid or to specifically acquire pets for primary prevention of asthma or allergic rhinitis in children should not be given.

Allergy. 2008 Jul;63(7):857-64.
Exposure to furry pets and the risk of asthma and allergic rhinitis: a meta-analysis.
Takkouche B, González-Barcala FJ, Etminan M, Fitzgerald M.
Department of Preventive Medicine, University of Santiago de Compostela, Santiago de Compostela, Spain.
Background: Exposure to pets has been implicated as a risk factor for asthma. However, this relation has been difficult to assess in individual studies because of the large potential of selection bias. We sought to examine the association between exposure to furry pets and asthma and allergic rhinitis by means of a meta-analysis.
Methods: We retrieved studies published in any language by searching systematically Medline (1966-March 2007), Embase, LILACS and ISI Proceedings computerized databases, and by examining manually the references of the original articles and reviews retrieved. We included cohort and case-control studies reporting relative risk estimates and confidence intervals of exposure to cats, dogs and unspecified furry animals and subsequent asthma and allergic rhinitis. We excluded cross-sectional studies and those studies that did not measure exposure but rather sensitization to pets.
Results: Thirty-two studies were included. For asthma, the pooled relative risk related to dog exposure was 1.14 (95% CI 1.01-1.29), that related to exposure to any furry pet was 1.39 (95% CI 1.00-1.95). Among cohort studies, exposure to cats yielded a relative risk of 0.72 (95% CI 0.55-0.93). For rhinitis, the pooled relative risk of exposure to any furry pet was 0.79 (95% CI 0.68-0.93).
Conclusions: Exposure to cats exerts a slight preventive effect on asthma, an effect that is more pronounced in cohort studies. On the contrary, exposure to dogs increases slightly the risk of asthma. Exposure to furry pets of undermined type is not conclusive. More studies with exact measurement of exposure are needed to elucidate the role of pet exposures in atopic diseases.

Phil Lieberman, M.D.

AAAAI - American Academy of Allergy Asthma & Immunology