Background <p>Recent studies have demonstrated that corticosteroid delivered by nasal irrigation is superior to nasal spray in the treatment of chronic rhinosinusitis patients who have undergone sinus surgery. However, the local cytotoxicity of both delivery methods has not been previously evaluated. In this study we aimed to evaluate the cytotoxicity of corticosteroid prepared nasal irrigation solution and commercially available corticosteroid nasal spray.</p> Methods <p>Primary human nasal epithelial air-liquid interface 3D cultures established from nasal brushes from patients with nasal diseases with polyps, and healthy nasal mucosa (<i>n</i> = 6 each) were used to assess the cytotoxicity of different drug concentrations. The following drugs were screened: budesonide rinse, mometasone rinse, mometasone spray, fluticasone spray, azelastine/fluticasone spray, xylometazoline drops and benzalkonium chloride. Nasal epithelial cell characterization at passage zero was evaluated with β- Tubulin and FOXJ1 immunostaining as well as fluorescence-activated cell sorting using epithelial cell marker (EpCAM-488). To assess the drug induced cytotoxicity, an Alamar Blue assay, transepithelial electrical resistance and optical microscopy were applied.</p> Results <p>Nasal irrigation using standard therapeutic concentrations of mometasone or budesonide demonstrated less cytotoxicity when compared to nasal spray of mometasone and fluticasone in stock concentration prescribed by the manufacturer. Nasal spray diluted by a factor of 10 demonstrated similar cytotoxicity to nasal irrigation using therapeutic concentration. This study reinforces the suspicion that it is not the drugs themselves but benzalkonium chloride that is the most involved in cytotoxicity.</p> Conclusion <p>Corticosteroid irrigation is less cytotoxic than corticosteroid spray to nasal epithelial cells.</p>