The severity of the disease can be correlated with nasal polyps enriched in eosinophils/IL-5 and, although ≥ 10 eosinophils per high power field are considered enough to determine an eosinophilic CRS, this cut-off value, the biopsy method, and the sampling location are still a matter of debate. The gene discussed is IL5; the disease is nasal cavity polyp.