Chronobiology of nasal chemosensitivity: do odor or trigeminal pain thresholds follow a circadian rhythm?

Odor and trigeminal pain thresholds were studied four times each at 24:00, 04:00, 08:00, 12:00, 16:00 and 20:00 h in randomized order on different days in five healthy male volunteers. No circadian rhythm of olfactory or trigeminal thresholds were observed. However, the variability of odor, but not pain thresholds, increased from 04:00 h (thresholds between 0.4 and 1.2 p.p.m.) to 16:00 h (thresholds between 0.1 and 2 p.p.m.). It is hypothesized that environmental influences contribute to this increase in variance.