This study aimed to investigate the effect of odorants on the salivary cortisol level during sleep and after awakening. Salivary cortisol was assessed because this glucocorticoid is involved in the activity of the hypothalamus-pituitary-adrenal (HPA) system, which is the dominant stress reaction pathway in the body. Fragrance of either lavender or jasmine were intermittently administered to the subjects in a counterbalanced order by using a specially manufactured olfactometer for the first 1 min of each 5-min interval for 6 h, while they were sleeping in a temperature- and humidity-controlled room. We found that the salivary cortisol level after awakening was significantly higher with lavender than with jasmine (p<0.01) and the control (p<0.05) conditions. Our results suggest that exposure to the fragrance of lavender during sleep can increase cortisol secretion after awakening, which in turn, may be reflected in the enhancement of HPA activity.
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