Chronic rhinosinusitis is an umbrella term for several phenotypes and mechanistically distinct inflammatory diseases of the nose and the paranasal sinuses affecting around 11% of the population in Europe and the USA. Approximately 20% of the patients present with uncontrolled disease despite adequate treatment, and revision surgery is common. While a clinical characterization alone does not improve treatment results, novel but expensive biologics have increasingly become available, but they require a better understanding of the mechanism. Mechanistic markers of disease may help to allocate the optimal drug to a patient, thus reducing undesirable side effects and avoiding unnecessary treatment and costs with respect to potential non-responders, thereby increasing responder rates and compliance.