Perceived irritation during ingestion of capsaicin or piperine: comparison of trigeminal and non-trigeminal areas.

The aim of this study was to investigate the perception of chemosensory irritation in the oropharyngeal region during the ingestion of irritants. In two experiments subjects sipped and swallowed small samples of an ascending concentration series of capsaicin or piperine and rated the intensity of sensations or irritation perceived at four locations: the anterior tongue, the posterior tongue, the roof of the mouth and the throat. Both experiments revealed that the responsiveness to irritation from capsaicin was significantly higher in the throat than at either the front or back of the tongue. There was no difference between irritation ratings for the throat and the roof of the mouth. Compared with capsaicin, the responsiveness to piperine was more uniform along the rostro-caudal axis; for example, irritation ratings for the throat were similar to those for the anterior tongue. These results support previous findings which indicated that the oral mucosae were not uniformly sensitive to chemical irritants, and suggest further that the throat, which is innervated by both the glossopharyngeal and vagus nerves, plays an important role in the perception of chemesthetic stimuli during ingestion.