Lower Olfactory Sensitivity in Retronasal Olfaction

OBJECTIVES: To directly compare orthonasal and retronasal olfactory function using the recently introduced odorant containers, which enable retronasal stimulation without gustatory or somatosensory involvement. DESIGN: Experimental study employing a within-subjects design. SETTING: Laboratory-based olfactory testing facility. PARTICIPANTS: Thirty-one healthy young adults (19 females; mean age 29.2 years, SD 5.9). MAIN OUTCOME MEASURES: We assessed odour threshold, discrimination and identification with procedures closely adapted from the Sniffin' Sticks test battery, implemented for both routes using odorant containers (instead of Sniffin'Sticks pens). In addition, we obtained global olfactory test scores and odour intensity ratings. RESULTS: Compared with orthonasal olfaction, retronasal olfaction was associated with significantly higher threshold scores, indicating lower sensitivity. We did not observe any significant differences between orthonasal and retronasal olfaction in odour discrimination or identification. In turn, a combined TDI score was significantly higher for orthonasal than retronasal stimulation. Odours were also rated as more intense when presented orthonasally. Notably, participants identified one odour (fish) with significantly lower accuracy in the retronasal condition. CONCLUSIONS: Retronasally presented odours are perceived as weaker and less detectable than orthonasal odours, despite similar discrimination and identification capacities. These findings highlight perceptual differences between the two olfactory routes and provide experimental validation for the odorant containers method in retronasal testing.