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Wise et al.

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• Policy Level: Option for breastfeeding for the specific purpose of AR prevention, based upon current evidence. In general, breastfeeding has been strongly recommended due to its multiple benefits. • Intervention: Breastfeeding is generally encouraged for at least 4 months due to its multiple benefits. When specifically related to the prevention of AR, breastfeeding is an option. VI.G.2. Childhood exposure to pets— Among subjects sensitized to pet allergens, exposure tends to exacerbate symptoms. However, the association of pet-keeping in childhood with the subsequent development of AR is more controversial, and difficult to establish. (See section VI.B. Risk factors for allergic rhinitis – Inhalant allergens (in utero and early childhood exposure) – Animal dander for additional information on this topic.) Prevalence of household pet ownership is used to estimate pet allergen exposure. However, pet owners are frequently contaminated with pet allergens, leading to generalized exposures via social contact. Therefore, a non-exposed reference population does not exist, limiting our ability to clearly understand the relationship between exposure to pet allergens and development of AR. The timing of pet allergen exposure early in life may be an important factor for the maturing immune system. Therefore, self-reported perinatal and newborn exposures are frequently analyzed. Few studies have measured the concentration of the major cat ( Felis catus ) allergen (Fel d 1) or the major dog ( Canis familiaris ) allergen (Can f 1) in home dust. Rather, most studies merely report exposure to cats and/or dogs, or furred pets, and some to rodents and birds. In a systemic review of epidemiologic studies of allergy and asthma, only 10 of 96 included studies reported avoidance of pets. 638 Additionally, studies may often fail to account for confounding variables such as a family history of pet allergy which, in turn, may predispose likely atopic children to pet avoidance. There is significant inconsistency with regard to pet ownership in childhood and the subsequent development of allergy. Demographic features related to pet-keeping, including race, urban vs rural environment, family size, and SES may help account for some of the conflicting results. A meta-analysis of 32 studies reported a lower prevalence of AR among subjects with furred pets in cross-sectional studies, and less asthma among cat-exposed subjects. 639 An extensive systematic review of 62 studies found different associations depending on study design. 640 In most of the birth cohort studies, dog exposure in early childhood was protective for sensitization against aeroallergens. 640,641 On the contrary, cross-sectional studies reported inconsistent associations between cat or dog exposure and sensitization as well as the subsequent development of atopic diseases later in life 562,640 (Table VI.G.2). The impact of pet avoidance on AR development is best evaluated via longitudinal birth cohort studies. A systematic review of 9 studies conducted solely in urban environments evaluated perinatal pet exposure. 642 Six studies found that exposure to dogs, or cats/dogs protected against allergic disease. Two studies found increased risk of allergy only in highly atopic families. Furthermore, in a cohort of 620 children with family history of allergic

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Int Forum Allergy Rhinol . Author manuscript; available in PMC 2020 June 10.