Eosinophilic chronic rhinosinusitis (ECRS) is a type of airway disease that involves nasal inflammation. Here, semaphorin protein was found to contribute to allergic reactions and development of nasal polyps in patients with ECRS. A research team found that an anti-semaphorin antibody could reduce nasal inflammation in a mouse model of ECRS and that semaphorin protein could be a new biomarker for ECRS in patients with nasal inflammation.