Essential oils have been used as remedies since ancient times for the treatment of numerous illnesses on account of their wide range of biological activities. Historical records show that essential oils were already in use more than 2000 years ago in ancient Egypt, India, Persia, Mesopotamia, and China to prevent illnesses, for the treatment of diseases and in religious ceremonies on account of their pleasant odors. Essential oil have drawn attention from scientists, practitioners, and therapists for their biological activities such as antibacterial, antifungal, antiviral, anti-inflammatory, antioxidant, anticancer, and antinociceptive properties. The use of essential oils in complementary therapies such as aromatherapy is popular in many countries and involves the administration of essential oils by inhalation, skin absorption, or ingestion for prophylactic medical care or active treatment.
Nowadays, aromatherapy is used worldwide to alleviate insomnia, depression, anxiety and some cognitive disorders. In the last 10 years, accumulating evidence has shown that the administration of essential oils exert measurable pharmacological effects and when used at an appropriate concentration, seems to be safe without showing adverse effects, which are common in several commercial psychotropic drugs. Recent preclinical and clinical studies have shown varying pharmacological responses in the nervous system leading to anxiolytic, antidepressant, sedative, and anticonvulsant effects. Experimentation in animal models has evidenced the involvement of multiple neurotransmitter systems in the mode of action of essential oils, resulting in measurable physiological effects in the brain. Additionally, clinical trials have demonstrated the influence of essential oils in physiological parameters such as blood pressure, heart rate, respiratory rate, brain waves composition, and cortisol serum levels with concomitant psychological effects. Although there is growing evidence of measurable effects of essential oils in animal brains, more clinical research is required to validate their influence in the human central nervous system. This will enable the development of essential oil-based drugs for the treatment of mental illnesses such as depression, anxiety and dementia.