POSTN and chronic rhinosinusitis with nasal polyps: In this study, we found higher levels of MMP‐9 in CRSwNP versus CRSsNP and identified that periostin induced the expression of MMP‐9 in fibroblasts, suggesting that periostin might be able to mediate, at least in part, the pathogenesis of CRSwNP via regulating the production of MMP‐9 in nasal fibroblasts.