The Multiple Trajectories of the Allergic March

The allergic march comprises the sequential appearance of a series of allergic comorbidities. However, variability in the onset and progression of allergic diseases generates a heterogeneous scenario that does not follow a linear and single trajectory. Almost half of the pediatric population presents at least 1 allergy symptom. However, only 4%-6% present multimorbidity, with several allergic diseases co-occurring. It has recently been shown that although they share etiological mechanisms and risk factors, allergic diseases arise independently. In most cases, progression is not consecutive, or at least not the same in all patients. TH2-mediated inflammation, epithelial barrier dysfunction, and genetic predisposition play a fundamental role in the etiology of allergic diseases, on which the interaction with the exposome acts decisively. Therefore, studying diseases from an omics point of view is essential when attempting to describe the various trajectories of allergic progression and to propose effective interventions to prevent multimorbidity. In this narrative review, we provide an overview of the current perception of the allergic march, including clinical observations, omics data, risk factors, and measures aimed at modifying its course or even preventing its onset.