Physicochemical Determinants and Functional Properties of the Senses of Irritation and Smell
Airborne volatile organic compounds (VOCs) are prime suspects in indoor air related illnesses (e.g., sick building syndrome). Frequent symptoms in those cases involve sensory responses of odor, nasal pungency (irritation), and eye irritation. We separated the trigeminal (pungent) from the olfactory (odor) response of the nose to a common set of substances by measuring nasal detection thresholds in subjects lacking a functional sense of smell (i.e., anosmics) and in matched-subjects with normal olfaction (i.e., normosmics). Eye irritation thresholds for the same compounds were also measured. Stimuli comprised homologous series of alcohols, acetates, ketones, and alkylbenzenes. Physicochemical properties change orderly and systematically in such series allowing to relate those properties with the observed sensory responses. In all series and for the three sensory modalities, thresholds decreased with carbon chain length. For nasal pungency — but not for odor — thresholds across chemical series bore a uniform linear relationship with simple physicochemical properties (e.g., saturated vapor concentration at room temperature). Eye irritation thresholds fell remarkably close to those of nasal pungency. Mixtures of VOCs can reach odor, pungency, and eye irritation thresholds when all components are below their individual thresholds.