Hormonal influences on chemoreception

The thresholds of human subjects can vary over minutes, hours, or days as much as between individuals. Therefore, measured interindividual thresholds may reflect nothing more than having been recorded at different levels of these sensitivity fluctuations (Stevens etal., 1988). 

Considering the biologically important 16-androstenes, humans are most sensitive to Sa-androst-lG-en-S-one (threshold 0.2 ppb). The detection threshold for 4,16-androstadien-3-one is 1.0 ppb and that for Sa-androstenol is 6.2 ppb (Amoore etal., 1977). 

Odor thresholds in humans appear to be more influenced by the environment than genetics. The detection thresholds for acetic acid, isobutyric acid, and cyclohexanone varied as much in monozygotic twins as in fraternal twins. Instead, smoking and diabetes were related to lower olfactory sensitivity, and body fatness and alcohol consumption to greater sensitivity to the latter two compounds (Hubert eta/., 1980). 

Thresholds are affected by the complexity of an odor. In tests with mixtures of 3,6, and 12 compounds, human subjects varied less from one another in their thresholds the more complex the odor was. The same trend was observed within individuals (Laska and Hudson, 1991). 

In general, perceived odor intensity is a power function of the odor concentration. The exponent is below 1, meaning that boosting the perceived intensity requires increasingly more odor production. As odor production becomes more and more costly, fine-tuning of chemoreception (instead of odor production) becomes the more attractive alternative evolutionarily. 

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