Introduction: Following the “hygiene hypothesis” and the increase in prevalence of atopic diseases such as allergic rhinitis, a plethora of studies have investigated the role of sibship composition as a protective factor, but findings are conflicting. Aim: To synthesize the global literature linking birth order and sibship size (number of siblings) to the risk of allergic rhinitis. Methods: Fifteen databases were systematically searched, with no restrictions on publication date or language. Observational studies with defined sibship composition (birth order or sibship size) as exposure and allergic rhinitis or allergic rhinoconjunctivitis (self-reported or clinically diagnosed) as outcome were eligible. Study selection, data extraction, and quality assessment was performed independently in pairs. Relevant data were summarized in tables. Comparable numerical data were analyzed using meta-analysis with robust variance estimation (RVE). Results: Seventy-six reports with >2 million subjects were identified. Being second- or later-born child was associated with protection against both current (pooled risk ratio [RR] 0.79, 95%CI 0.73-0.86) and ever (RR 0.77, 95%CI 0.68-0.88) allergic rhinitis. Having siblings, regardless of birth order, was associated with a decreased risk of current allergic rhinitis (RR 0.89, 95% CI 0.83-0.95) and allergic rhinoconjunctivitis (RR 0.92, 95%CI 0.86-0.98). These effects were unchanged across age, time period, and geographical regions. Conclusion: Our findings indicate that primarily, a higher birth order, and to a lesser extent the number of siblings, is associated with a lower risk of developing allergic rhinitis.

Recent reports indiciate that the prevelance of food allergy is increasing, but accurate estimates remain a challenge due to cross-reactivity and limited use of precise diagnostic methods. Component-resolved diagnostics (CRD), in which sensitization to individual molecular components of whole food allergen extracts is measured, is emerging as a promising tool for evaluation of sensitization profiles. In this systematic review, we summarized estimates of prevalence of sensitization to food allergen components in the general population in Europe. We searched seven databases with no restrictions on publication date or language. Two reviewers independently screened the literature and appraised the risk of bias in the included studies. From 4,776 de-duplicated records, five studies, with low to moderate overall risk of bias, were included and narratively synthesized. Forty-six components from 18 foods were investigated. Overall, the prevalence of sensitization was low, particularly for major allergens, and non-existent for 10 components (0% [95% CI 0-0.8]). The highest prevalence was seen for PR-10 proteins, such as Cor a 1.04 (13.6% [95% CI 10.9-16.9]). There were not enough studies to discern regional differences or perfom meta-analysis, highlighting the need for more population-representative studies in order to elucidate patterns of sensitization to food allergen components in Europe.