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Wise et al.

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Mites— There are 6 studies on the topic of early mite exposure and the development of AR (Table VI.B-1). Most of the studies failed to demonstrate an association between early exposure to mites and the development of AR. 468,516-519 Marinho et al. 520 reported that early exposure to HDM is not a protective factor for current AR, and Kim et al. 521 proposed exposure to spider mites as a risk factor for AR. Interestingly, pets may be a relevant source of mites, as their fur is often settled by mites; this association may confound AR evaluation and treatment. Ultimately, the studies on early mite exposure and the development of AR are conflicting and additional research is needed. • Aggregate Grade of Evidence: C (Level 2b: 5 studies; Level 3b: 1 study; Table VI.B-1). Pollens— There are only 2 studies that addressed the impact of early pollen exposure on AR (Table VI.B-2). Kihlström et al. 519 reported no association to allergic rhinoconjunctivitis whereas Erbas et al. 481 showed that pollen exposure during infancy is a risk factor for hay fever. • Aggregate Grade of Evidence: C (Level 2b: 1 study; Level 3b: 1 study; Table VI.B-2). Animal dander— Numerous studies have evaluated the association between early exposure to animal dander and subsequent development of AR, with conflicting results (Table VI.B-3). Studies are divided according to the findings: positive studies (reporting a protective effect on AR development 522-535 ), negative studies, (showing that early exposure to pets represents a risk factor for AR 523,536-542 ), and neutral studies (reporting that early exposure to animal dander is not associated with AR 468,517,518,520,524,528,530,532,536,538,539,543-554 ). Additional factors should be considered: pet age, gender, and species; number of household pets; home characteristics; atopic predisposition of the pet owners; and others. Considering these complex variables, debate regarding the influence of early pet exposure on developing allergic disease remains unresolved. Thus, evidence-based guidelines regarding having pets at home cannot be established. (See section VI.G.2. Risk factors for allergic rhinitis – Protective factors against allergic rhinitis – Childhood exposure to pets for additional information on this topic.) • Aggregate Grade of Evidence: C (Level 2b: 15 studies; Level 3b: 24 studies; Table VI.B-3). Fungal allergens— Several studies have explored the role of early exposure to fungal allergens as a predisposing factor for AR (Table VI.B-4). Most studies demonstrated evidence that early exposure to fungal allergens represents a risk factor for AR development. 527,538,551,553,555-560 However, 3 studies demonstrated that early exposure to fungal allergens is not associated with AR. 465,542,557 Home moisture level, which is closely and positively associated with the presence of fungal allergens in the home, may be a confounding factor in interpreting the evidence on fungal exposure and AR. Ambient humidity may an intrinsic risk factor, but high moisture is also associated with increased level of mites, as mites grow in presence of elevated moisture. Moisture can be easily

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