Subjective olfactory desensitization and recovery in humans

Adaptation to smells is a well-known phenomenon and appears to be one of the major characteristics of olfaction. However, no standardized protocols for the psychophysical measurement of olfactory adaptation and recovery are available to date. Twenty normosmic participants were included. Hydrogen sulfide (H2S) and phenylethyl alcohol were used in different concentrations based on air dilution olfactometry. Volunteers were exposed to a constant flow of odorous air until perception disappeared completely. For testing recovery, the volunteers were exposed to a reference stimulus following complete self-desensitization with the same odor. The subjects were then again exposed to the same odorant after recovery periods of different lengths and instructed to rate stimulus intensity. The time to complete desensitization increased with increasing stimulus concentration for both odorants. Subjects desensitized more rapidly using H2S. Olfactory adaptation led to a reduction in stimulus intensity for the subsequent identical stimulation. Longer recovery periods resulted in increased intensity of the subsequent stimulus independent of the stimulus used. The results confirm current knowledge regarding the dynamics of olfactory adaptation and demonstrate differences in olfactory desensitization between the 2 odorants used. Olfactory recovery was independent of the odorant used, indicating that olfactory recovery after complete desensitization may be a uniform process.