Type 2 inflammation, particularly relevant to CRSwNP, involves epithelial-derived mediators such as thymic stromal lymphopoietin (TSLP), IL-25, and IL-33 and is defined by the presence of Th2 cytokines (IL-4, IL-5, and IL-13) and eosinophilic infiltration; downstream effects include increased mucus-related gene activity and changes in epithelial transport that may interact with other inflammatory programs. This evidence concerns the gene IL4 and chronic rhinosinusitis with nasal polyps.