Does allergy cause chronic rhinosinusitis with nasal polyps?

Chronic rhinosinusitis (CRS) is a multifactorial disease due to chronic inflammation of sino-nasal mucosa that persists for more than 12 weeks. Since the first edition of EPOS guidelines, CRS has been divided into two main phenotypes: CRS with nasal polyposis (CRSwNP) and CRS without nasal polyposis (CRSsNP). In recent years, several authors agreed that CRS is not a uniform disease process but rather includes different phenotypes and endotypes. Differences may be observed in terms of risk factors, co-morbid conditions associated with CRS and disease control by medical treatment and surgery. The role of allergy in chronic rhinosinusitis (CRS) has been largely discussed in the literature, but nevertheless it remains controversial. Allergy and CRS are very prevalent diseases and frequently co-occur; however, direct causality has never been clearly demonstrated. Because the association between the two diseases has not been clear for years, making an evidence-based decision of whether to evaluate or treat allergies in CRS patients was difficult. Recently, it is clear that the prevalence of allergy is variable between the different subtypes of CRSwNP and the association seems to be very strong particularly with allergic fungal rhinosinusitis (AFRS) and central compartment atopic disease (CCAD).