NASAL PUNGENCY AND ODOR OF HOMOLOGOUS ALDEHYDES AND CARBOXYLIC-ACIDS

Airborne substances can stimulate both the olfactory and the trigemina l nerve in the nose, giving rise to odor and pungent (irritant) sensat ions, respectively. Nose, eye, and throat irritation constitute common adverse effects in indoor environments. We measured odor and nasal pu ngency thresholds for homologous aliphatic aldehydes (butanal through octanal) and carboxylic acids (formic, acetic, butanoic, hexanoic, and octanoic). Nasal pungency was measured in subjects lacking olfaction (i.e., anosmics) to avoid odor biases. Similar to other homologous ser ies, odor and pungency thresholds declined (i.e., sensory potency incr eased) with increasing carbon chain length. A previously derived quant itative structure-activity relationship (QSAR) based on solvation ener gies predicted all nasal pungency thresholds, except for acetic acid, implying that a key step in the mechanism for threshold pungency invol ves transfer of the inhaled substance from the vapor phase to the rece ptive biological phase. In contrast, acetic acid - with a pungency thr eshold lower than predicted - is likely to produce threshold pungency through direct chemical reaction with the mucosa. Both in the series s tudied here and in those studied previously, we reach a member at long er chain-lengths beyond which pungency fades. The evidence suggests a biological cutoff, presumably based upon molecular size, across the va rious series.