Abstract

Airborne substances can stimulate both the olfactory and the trigeminal nerve in the nose, giving rise to odor and pungent sensations, respectively. Nose, eye, and throat irritation constitute common adverse effects in indoor environments. We measured odor and nasal pungency thresholds for homologous aliphatic aldehydes and carboxylic acids. Nasal pungency was measured in subjects lacking olfaction to avoid odor biases. Similar to other homologous series, odor and pungency thresholds declined with increasing carbon chain length. A previously derived quantitative structure-activity relationship based on solvation energies predicted all nasal pungency thresholds, except for acetic acid, implying that a key step in the mechanism for threshold pungency involves transfer of the inhaled substance from the vapor phase to the receptive biological phase. In contrast, acetic acid — with a pungency threshold lower than predicted — is likely to produce threshold pungency through direct chemical reaction with the mucosa. Both in the series studied here and in those studied previously, we reach a member at longer chain-lengths beyond which pungency fades. The evidence suggests a biological cut-off, presumably based upon molecular size, across the various series.