Background: The sphenopalatine artery (SPA) runs in close proximity to the branches of the trigeminal nerve and to the sympathetic and parasympathetic secretomotor fibers. In refractory epistaxis, monopolar cautery of the SPA during surgery is of widespread use. The effect of coagulation on adjacent trigeminal and parasympathetic branches, and thus intranasal sensitivity and secretory function, is unknown. Methods: To investigate intranasal trigeminal function (INTF) by means of CO₂ stimuli intranasally, at baseline and after decongestion, before and after local anaesthesia (xylocaine) in healthy subjects and after monopolar cautery in patients treated for refractory epistaxis. In the latter, INTF and secretory function were tested by comparing the treated with the untreated side. Nasal and lacrimal secretions were measured with intranasal sponges and Schirmer’s tests. Setting: Monocentric cohort study in tertiary referral centre. Results: A total of 37 healthy participants and 17 patients were included. Nasal decongestion had no effect on CO₂ measurements, whereas local anaesthesia significantly decreased INTF in healthy subjects. In patients, the operated side showed significantly lower INTF, lower nasal secretory function but no significant changes in lacrimal function. Conclusion: Local anaesthesia and surgical treatments have measurable effects on INTF. Monopolar cautery of the SPA and its branches affects nasal secretory function. These effects may lead to symptoms and surgeons should be aware of the potential harm in epistaxis treatments.