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Odor Detection Threshold

المؤلف:  Kim E. Barrett, Susan M. Barman, Heddwen L. Brooks, Jason X.-J. Yuan

المصدر:  Ganongs Review of Medical Physiology

الجزء والصفحة:  25th E, P220

2026-11-03

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Odor-producing molecules (odorants) are generally small, containing from 3 to 20 carbon atoms; and molecules with the same number of carbon atoms but different structural configurations have different odors. Relatively high water and lipid solubility is characteristic of substances with strong odors. Some common abnormalities in odor detection are described in Clinical Box 1.

Clinical Box 1

The odor detection thresholds are the lowest concentration of a chemical that can be detected. The wide range of thresholds illustrates the remarkable sensitivity of the odorant receptors. Some examples of substances detected at very low concentrations include hydrogen sulfide (0.0005 parts per million, ppm), acetic acid (0.016 ppm), kerosene (0.1 ppm), and gasoline (0.3 ppm). On the other end of the spectrum, some toxic substances are essentially odorless; they have odor detection thresholds higher than lethal concentrations. An example is carbon dioxide, which is detected at 74,000 ppm but is lethal at 50,000 ppm. Not all individuals have the same odor detection threshold for a given odorant. While one person may detect and recognize an odorant at a particular concentration, another person may barely notice it.

Olfactory discrimination is remarkable. On the other hand, determination of differences in the intensity of any given odor is poor. The concentration of an odor-producing substance must be changed by about 30% before a difference can be detected. The comparable visual discrimination thresh old is a 1% change in light intensity. The direction from which a smell comes may be indicated by the slight difference in the time of arrival of odorant molecules in the two nostrils.