# Essential Oils, Phytoncides, Aromachology, and Aromatherapy--A Review
## 6 Essential Oils and Their Health Outcomes  
The essential oils taken from plants without extracting peculiar phytoncides are used to treat stress and pain. The aroma-enriched essential oils possess some rejuvenating effects in humans. Major health disorders, such as hypertension and cardiovascular diseases, are associated with stress and anxiety. Stress disturbs cognitive function, behavior, mood, and thinking skills. Mental, physical, and emotional problems interfere with individuals' learning capabilities, where stress and anxiety presumably cause hypertension and mortality. The combination of four essential aroma oils, laverd (_Lavandula angustifolia_; _L. angustifolia_), ylang-ylang (_Cananga odorata_; _C. odorata_), marjoram (_Origanum majorana_; _O. majorana_), and neroli (_Citrus aurantium_; _C. aurantium_), can decrease systolic and diastolic blood pressure and reduce salivary cortisol in prehypertensive and hypertensive patients [154]. Chronic mental stress also initiates sudden death or myocardial infarctions [155]. Besides health disorders and irreversible diseases, stress also negatively impacts human emotions. Managing stress can address those negative consequences [156]. Aroma oils can be inhaled or massaged over the skin; the applied oil vaporizes and stimulates the olfactory system [157]. _L. angustifolia_ aroma oil reduces mental stress and increases arousal [158]. Likewise, Yuzu essential oil (_Citrus junos Sieb. ex [PERSON]_) reduces negative emotional stress [159, 160] and inhibits platelet aggregation, which could be helpful in individuals with a high risk of cardiovascular disease [161]. Essential oils promote de-stressing effects such as relaxation and sleep. [PERSON] and his team reported that the inhalation of ylang-ylang essential oil decreases blood pressure [162], reduces vibrations and promotes relaxation [163], and increases alertness [164]. Aromatherapy reduces blood pressure, anxiety [165], and agitation [166] in dementia patients. Aromatherapy with essential oils such as linalool, santalol, cedrol, piperonal, true laverd, and sweet orange oil improved sleep in the elderly with dementia [167]. The inhalation of essential oils seems to lessen depression and increase the sleep quality of postpartum mothers [168, 169]. The essential oils of sandalwood, sweet majoram, and laverd are purportedly used in sedation, relaxation, treating anxiety, and relieving irritability, loneliness, insomnia, and depression [170, 171, 172]. Marjoram lowers the activity of the sympathetic nervous system and kindles the parasympathetic nervous system, which increases vasodilation and reduces blood pressure. Neroli essential oil soothes emotions, gives comfort, and reduces vibrations resulting from shock or fear [163]. [PERSON] and [PERSON] evaluated the stress-reducing effect of laverdora. The results show that laverdora promoted post-stress cognitive performance. Hence, the protective effects of laverdora on working memory prove that aromas protect cognitive function after stress [173]. Laverdora arom lessens cardiac excitation, reduces BP, and is effective in hypertension and palpitations [154]. The aroma from _Ltisea cubeba_ (_L.cubeba_) is used in treating cognitive discomfort. It was found to improve mood and reduce stress and confusion by reducing the salivary cortisol level in healthy individuals [174] (Table 2). Pain is another discomfort, not only caused by physical illness but also by psychological distress. In a contradictory way, psychological distress can induce progressive pain. [PERSON]'s concept of pain explains that pain is a person's suffering in social, physical, psychological, and spiritual aspects [175]. Pain induces fear, which further deteriorates social interactions and produces anxiety, depression, and stress [176, 177, 178]. The aroma of agave (_Polianthes tuberosa_; _P. tuberosa_) essential oil reduced test anxiety [179]. The aroma of laverd and bergamot EO can act as an antidepressant and relaxant. Pleasant odors encourage a positive mood [170] and alleviate negative emotions [180].