Tangerine (Citrus tangerina) is one of the most important crops of Thailand with a total harvest that exceeds 100,000 tons. Citrus essential oils are widely used as aromatherapy and medicinal agents. The effect of tangerine essential oil on human brain waves and sleep activity has not been reported. In the present study, we therefore evaluated these effects of tangerine essential oil by measurement of electroencephalography (EEG) activity with 32 channel platforms according to the international 10–20 system in 10 male and 10 female subjects. Then the sleep onset latency was studied to further confirm the effect on sleep activity. The results revealed that different concentrations, subthreshold to suprathreshold, of tangerine oil gave different brain responses. Undiluted tangerine oil inhalation reduced slow and fast alpha wave powers and elevated low and mid beta wave powers. The subthreshold and threshold dilution showed the opposite effect to the brain compared with suprathreshold concentration. Inhalation of threshold concentration showed effectively decreased alpha and beta wave powers and increased theta wave power, which emphasize its sedative effect. The reduction of sleep onset latency was confirmed with the implementation of the observed sedative effect of tangerine oil.

Essential oils are volatile fragrance liquids extracted from plants, and their compound annual growth rate is expected to expand to 8.6% from 2019 to 2025, according to Grand View Research. Essential oils have several domains of application, such as in the food and beverage industry, in cosmetics, as well as for medicinal use. In this study, Michelia alba essential oil was extracted from leaves and was rich in linalool components as found in lavender and jasmine oil. The effects of inhaling michelia oil on human brainwaves still need to be elucidated. Ten male and ten female subjects were recruited. Thirty-two-channel electroencephalography was recorded. The raw data were spectrally analyzed for slow alpha, fast alpha, low beta, mid beta, and high beta activities. The results demonstrate that michelia leaf oil could reduce the alertness level observed by beta wave decrease and fast alpha wave activity increase. The inhalation of pure linalool showed virtually identical responses as the michelia oil inhalation. In conclusion, the sedative effects of michelia oil inhalation might originate from its major linalool component.