Phenotypes and endotypes
The concepts of phenotype and endotype have been increasingly used to characterize variants under a wider disease umbrella, referring to either the apparent differentiating features (phenotype) or the underlying mechanisms (endotype). While disease variability is clearly the norm rather than the exception in regards to most allergic diseases, the realization that treatment response may vary radially between groups, has given impetus to this approach [23]. Unfortunately, lack of pathognomonic biomarkers, considerable overlap and unstable temporal dynamics have not allowed, for the time being, the construction of conclusive phenotype and/or endotype-based guidelines [24]. Nevertheless, clear distinctions and differentiating factors can be drawn, such as the hormonal or gustatory rhinitis – all part of the non-allergic rhinitis spectrum. A distinct pediatric example is rhinitis in infants, which presents additional challenges in management choices, requiring further evidence [25].