A narrative review on allergy and exposure to domestic and non-domestic animals: favorable and unfavorable effects.

Summary: The aim of this contribution was to highlight the "favorable" and "unfavorable" roles of domestic and non-domestic animals on airway sensitization processes and on the type/severity of the clinical symptoms induced by their exposure. We performed a literature research in MEDLINE for allergic manifestations and animals. Pets can be "allergy friends" through mechanisms related to hygiene hypothesis and translational aspects, the dual role of IgG4 antibodies for pets, and their promising role as healthcare service animals (dogs). On the contrary, animals can be "allergy enemies" when inducing allergic sensitization and  respiratory symptoms (sometimes leading to severe reactions), and also due to cross reactivity with other pets allergens, indirect exposure and ubiquity of their allergens, cross reactivity between Can f 5 and human prostate-specific antigen (PSA). Moreover, in some cases they can trigger anaphylaxis, induce occupational asthma, and act as pests. Finally, we must outline the modest efficacy of allergen immunotherapy (AIT) for their allergens. From a strictly allergological perspective, it is evident that the "negative" aspects resulting from exposure to domestic / non-domestic animals outweigh the "positive" aspects. As a consequence, it is up to humans to seek new ways to balance the pros and cons by exploring research areas that can allow the best possible coexistence with subjects at risk of allergy with domestic and non-domestic animals.