What do topical nasal sprays do to the nasal mucosa in the long term? This study reports the effect of corticosteroids, antihistamines and common preservatives in nasal sprays, benzalkonium chloride (BKC) and potassium sorbate (PS), on an in-vitro model of human nasal mucosa. Fluticasone and azelastine were both shown to cause a remarkable rapid and irreversible decrease in ciliary beating frequency when applied undiluted or at 50% concentration. BKC, a common preservative in nasal steroid sprays including fluticasone proprionate and azelastine hydrochloride, induced ciliary stasis at half the concentration found in commercial preparations. Budesonide and potassium sorbate both had reversible or minor effects on ciliary motility. The long-term effect of topical nasal preparations on mucosa is controversial, and the results of this study must be interpreted with caution. There is little evidence to support the idea that fluticasone or azelastine have irreversible ciliotoxic effects from clinical observation, and indeed the authors of the study state that although their findings are in line with several other cell culture studies, these adverse effects cannot be replicated in vivo. This is likely to be due to the dilutional effect of nasal secretions and protective mechanisms which are not present in the in vitro model. Until further studies are done in vivo, this remains a cautionary tale that laboratory findings do not translate easily in complex biological systems.