Essential oils are volatile, aromatic compounds and the pure essence of plant extracts. The plants undergo a special distillation process in which the essential oil is separated from its plant part.

We encounter essential oils as part of herbs and spices every day in our everyday lives: whether it is cinnamon on our morning porridge, a cup of peppermint tea in the afternoon or basil on our spaghetti in the evening – we always consume volatile essential oil compounds.

Diverse application possibilities

Essential oils are also used in their concentrated form as dietary supplements and topically, i.e. applied to the skin. The most common form, however, is inhalation, where the oil is inhaled using steam.

Essential oils are often used in cooking or baking as a substitute for fresh or dried spices and herbs - for example, to give baked goods a particularly intense orange or lemon aroma. However, the dosage should be very careful, as the aroma is much more concentrated and therefore more intense than with conventional spices.

The addition of essential oils to drinks such as tea, smoothies, water or milk is becoming increasingly popular.

When essential oils are consumed as part of food or concentrated as a supplement, they enter the bloodstream through the gastrointestinal tract. Essential oils are fat-soluble, so they are easily transported to all organs of the body, including the brain. Then, like everything we consume, essential oils are metabolized by the liver and other organs and eventually excreted.

But the external, topical application of essential oils has also proven itself over many years. For example, adding a few drops of oil to a warm bath or as a hot or cold compress by soaking a towel in water, adding essential oils and then applying to the desired area. Adding essential oil to a lotion or moisturizer that is then applied to the skin is also a proven way to enjoy the benefits of essential oils. Of course, sensitive areas such as the skin around the eyes, eyes and inner ears as well as injured skin should be avoided.

The biochemistry behind essential oils: health effects and connections

But in addition to the emotional component, which anyone who has ever come into contact with high-quality essential oils can immediately understand, there are also more and more scientific studies that examine the health benefits of essential oils on a biochemical level.

The nose, with its approximately 350 scent receptors, naturally plays a crucial role in the perception of scents. Biochemically, the messenger molecule cAMP plays an important role, converting the scent information triggered by the scent receptors in the olfactory sensory cells into an electrical impulse that is transmitted to the brain via the central nervous system.

But there are scent receptors not only in the nose, but in all cells of the body, for example in fatty tissue, but also in organs such as the lungs, heart or kidneys, where you would not normally expect them. Outside of the nose, however, these scent receptors have nothing to do with "smelling" in the true sense of the word, so a term such as "chemoreceptors" would probably be more appropriate. If a molecule activates one of these receptors, this can stimulate the cells to release messenger substances, divide or move.According to research by Professor Klatt from the Ruhr University Bochum, these receptors also influence cell death – which could open up exciting possibilities in cancer therapies, for example.

Between 5 and 80 different types of odorant receptors can be found in each tissue. And there, these odorant receptors control a variety of different signaling pathways that can have very different effects at the cellular level:

For example, an odor receptor for violet scent in the pigment cells of the skin inhibits cell growth, while in the retina it can promote cell growth. Likewise, the odor receptor for sandalwood can accelerate hair growth and wound healing, whereas it can inhibit the proliferation of leukemia cells.

The scents that activate these receptors are not only those that enter the body through the skin, food or breathing, but also those that are produced by microbes in the intestines, bronchi or on the skin.

From this knowledge and the fact that currently only 50 of the 350 odorant receptors found in humans are known, completely new therapeutic approaches for the future can be derived. Professor Hanns Hatt from the Ruhr University Bochum explains:

"The further decoding of olfactory receptors, which are present in large quantities in human tissues, as well as the decoding of their diverse effects and the associated activating substances will open up previously unimagined possibilities for pharmaceutical treatment."

Use in cancer therapy also appears promising, as odor receptors are often found in large quantities in cancer cells and their receptor types can differ from those of healthy cells. Therefore, odor receptors could be considered as tumor markers in diagnostics. But Professor Hatt also sees potential in therapy, particularly in tumors such as colon or bladder cancer, which are easily accessible to external scents.

(Source: Lee, Sung Joon; Depoortere, Inge; Hatt, Hanns. Nature Reviews Drug Discovery 18, 116-138 (2019))

Current studies on the individual essential oils

bergamot

The essential oil extracted from bergamot is used worldwide in aromatherapy to To relieve pain, facilitate sleep induction and/or minimize the effects of stress-related anxiety. Preclinical pharmacological data show that bergamot essential oil (BEO) modulates specific neurotransmissions and exhibits a relaxing, anti-anxiety effect. Several studies on essential oils indicate a role for serotonergic (5-HT) neurotransmission in anxiety. Source: https://pubmed.ncbi.nlm.nih.gov/32283606/

Preclinical studies have recently shown that bergamot essential oil has remarkable neurobiological effects. It can influence synaptic transmission and has shown neuroprotective properties. Bergamot oil is also commonly used in aromatherapy to minimize the symptoms of stress-related anxiety and mild mood disorders.

The following study tested endocrinological, physiological and psychological effects of bergamot oil steam inhalation on 41 healthy women in a random crossover study design. The volunteers were exposed to 3 experimental setups (rest (R), rest + steam (RW), rest + steam + bergamot essential oil (RWB)) for 15 minutes each. Immediately after each setup, saliva samples were taken and cortisol levels measured:

The cortisol level of RWB was significantly lower compared to the R setup.The results of this study show that bergamot oil combined with steam produces psychological and physiological effects in a relatively short period of time. Source: https://pubmed.ncbi.nlm.nih.gov/25824404/

The following study investigated the anxiolytic/sedative effects of bergamot oil in rats. Analysis of the data suggests that BEO induces anxiolytic/relaxant effects in animal behavioral tasks: https://pubmed.ncbi.nlm.nih.gov/28398260/

Bergamot essential oil is also increasingly being used in dementia therapy. Cognitive impairment is a serious but not the only problem with dementia: behavioral and psychological syndromes known as neuropsychiatric symptoms of dementia significantly reduce the quality of life. The collection of symptoms includes anxiety, depression, wandering, delusions, hallucinations, misidentifications, agitation and aggression.

Aromatherapy provides positive results in controlling agitation as one of the central symptoms. Dementia patients are often unable to verbalize pain, which leads to unrelieved symptoms and contributes to agitation. Bergamot essential oil provides extensive preclinical evidence of analgesic (i.e. pain-relieving) properties. Bergamot essential oil induces the anxiolytic effect typical of benzodiazepines without sedation. Source: https://pubmed.ncbi.nlm.nih.gov/31284573/

citronella

Mosquito-borne diseases such as malaria, yellow fever or dengue are the main cause of relevant morbidity and mortality in livestock and humans worldwide. Several reports of side effects of synthetic insect repellents such as skin rash, hives or damage to brain functions in children are available in the literature. Therefore, natural insect repellents such as essential oils have been recently explored as an alternative. One such essential oil that has been extensively studied is citronella oil. This essential oil has shown good efficacy against mosquitoes. It is a mixture of components including citronellal, citronellol, geraniol as the main constituents, which contribute to various activities (antimicrobial, antioxidant, antispasmodic and wound healing) in addition to mosquito repellent activity.

https://pubmed.ncbi.nlm.nih.gov/30019646/

eucalyptus oil

Cineole is found primarily in eucalyptus and laurel and is perceived by humans via the olfactory nerve, and at higher concentrations also via the trigeminal nerve - a cranial nerve that causes, for example, the burning and feeling of heat when eating chili and the feeling of cold when eating menthol, which also occurs when in contact with cineole. By activating the trigeminal nerve, also known as the "warning nerve", cineole makes you more alert and invigorated.

geranium

Geraniol is found mainly in roses and geraniums. It has a calming, relaxing effect and makes us more relaxed. Biochemically, geraniol increases the effect of the body's own neurotransmitter GABA, which is crucial for inducing and maintaining sleep. Pharmaceutical tranquilizers such as benzodiazepines or barbiturates exert their effect in the same way by binding to the corresponding GABA receptor.

Breast cancer is associated with high morbidity and mortality. Chemoresistance and toxicity are the main causes that limit treatment success in aggressive breast cancer cases. The following study investigated the possible effects of frankincense, pine needle and geranium essential oils on breast cancer cell viability, proliferation, migration and invasion and the possible mechanisms involved.MCF-7 breast cancer cells were treated with the above essential oils and it was shown that these essential oils suppressed cell viability, proliferation, migration and invasion in human MCF-7 breast cancer cells.

Further data showed that frankincense, pine needle and geranium essential oils induced apoptosis but did not affect cell cycle progression. Consistent with the in vitro activities, frankincense essential oil was effective in inhibiting tumor growth and inducing tumor cell apoptosis in a human breast cancer mouse model. Furthermore, these 3 essential oils modulated the activity of the AMPK/mTOR signaling pathway. In conclusion, the present study demonstrated that frankincense, pine needle and geranium essential oils were involved in BC cell progression possibly via the AMPK/mTOR pathway. Source: https://pubmed.ncbi.nlm.nih.gov/29115548/

COVID-19 has been declared the most severe health emergency in modern history worldwide. It has been found that the angiotensin-converting enzyme 2 (ACE2) receptor, a host cell receptor, plays a crucial role in viral cell entry. Therefore, ACE2 blockers may be a potential target for antiviral intervention. In the following study, the ACE2 inhibitory effect of 10 essential oils was investigated. Among them, geranium and lemon oils showed significant ACE2 inhibitory effect in epithelial cells. In addition, immunoblotting and qPCR analyses also confirmed that geranium and lemon oil possess strong ACE2 inhibitory effect. The results suggest that geranium and lemon essential oils and their derived compounds are valuable natural antiviral agents that can help prevent SARS-CoV-2/COVID-19 from entering the human body. Source: https://pubmed.ncbi.nlm.nih.gov/32575476/

Acinetobacter species are among the so-called "hospital germs" and are organisms that can cause purulent infections in any organ system. Their resistance to some antibiotics and their ability to produce biofilms contribute to their virulence. The aim of the following study was to determine the antibacterial properties of cinnamon, lavender and geranium essential oils against bacteria of the genus Acinetobacter isolated from several clinical materials and from the hospital environment. Result of the study: These three essential oils can be best used in combating infections caused by bacteria of the genus Acinetobacter as a component of formulations for hygiene and disinfection of the hospital environment. Source: https://pubmed.ncbi.nlm.nih.gov/25514231/

Immortelle & Lavender

Lavender and immortelle essential oils are widely used to treat a number of human diseases. The aim of the following study was to investigate the cyto-/genotoxic effects of lavender and immortelle oil on plant cells (Allium cepa) and human lymphocytes, as well as their antimicrobial potential on nine bacterial and fungal strains. The results confirm that lavender and immortelle essential oils showed cyto-/genotoxic effects in both plant and human cells, as well as antimicrobial properties. Further studies are needed to substantiate these findings. Source: https://pubmed.ncbi.nlm.nih.gov/30607990/

lavender

Essential oils distilled from members of the genus Lavandula have been used both cosmetically and therapeutically for centuries.Although there is considerable anecdotal information about the biological activity of these oils, much of it has long been unsupported by scientific or clinical evidence.

Claims for lavender oil include that it is antibacterial, antifungal, digestive (gentle muscle relaxation), sedative, antidepressant, and effective on burns and insect bites.

However, there is now both scientific and clinical data supporting the traditional use of lavender; Source: https://pubmed.ncbi.nlm.nih.gov/12112282/

Example: https://pubmed.ncbi.nlm.nih.gov/22517298/ This study suggests that inhalation of lavender essential oil may be an effective and safe treatment in the acute management of migraine headaches.

Aromatherapy is also a promising therapeutic alternative for relieving depressive symptoms in depression. Lavender essential oil has been the focus of clinical studies due to its positive effects on mood. An animal model of chronic administration of high-dose corticosterone to induce depression- and anxiety-like behavior and reduced neurogenesis was used to investigate the biological changes brought about by aromatherapy. 24 adult male Sprague-Dawley rats were randomly divided into four groups. Behavioral tests were performed at the end of the 14-day treatment period. The results showed that treatment with lavender essential oil improved depression-like behavior induced by chronic administration of corticosterone. (Source: https://pubmed.ncbi.nlm.nih.gov/30825591/)

A 2019 review considered human clinical trials (n = 7), animal studies (n = 5), in vitro studies (n = 2), and previously conducted reviews (n = 6) and found a faster wound healing rate, increased expression of collagen, and increased activity of proteins involved in the tissue remodeling process in wounds treated with lavender essential oil. Thus, the current literature clearly indicates a potential therapeutic benefit of lavender essential oil in wound healing. However, standardization of the chemical composition and additional high-quality human clinical trials are needed to further evaluate the safety and efficacy of lavender essential oil in clinical practice. Source: https://pubmed.ncbi.nlm.nih.gov/32589447/

Even in cases of knee osteoarthritis, an aromatherapy massage with essential lavender oil was able to relieve the pain of those affected. However, further studies are needed to confirm the results of this study. Source: https://pubmed.ncbi.nlm.nih.gov/27863613/

Lemongrass

The following study shows promising antifungal (antimicrobial effect against diseases caused by fungi) activity of lemongrass essential oil against Candida albicans, Candida tropicalis and Aspergillus niger. It concludes that lemongrass essential oil has remarkable potential for the development of drugs to treat fungal infections and skin inflammations, which should be investigated in future studies. Source: https://pubmed.ncbi.nlm.nih.gov/25242268/

Lemongrass essential oil is also used to repel mosquitoes. The following study investigated the spatial repellency of essential oils on the tropical yellow fever mosquito (Aedes aegypti) and on local mosquito populations in coastal British Columbia (Canada).In laboratory experiments following World Health Organization protocols, three of the essential oils tested were found to be repellent to the yellow fever mosquito: cinnamon bark, lemongrass and rosemary. Source: https://pubmed.ncbi.nlm.nih.gov/31143941/

mandarin

The effects of mandarin peel essential oil were studied on the growth of two human tumor cell lines (lung adenocarcinoma A549 and hepatocarcinoma HepG2). The essential oil was obtained by cold pressing. The mandarin essential oil showed a strong dose-dependent effect on the growth inhibition of the mentioned tumor cell lines. The essential oil was more effective in A549 than in HepG2 cells. It is likely that minor components could have additive or synergistic effects. Therefore, mandarin essential oil could lead to the development of antitumor drugs or complementary and alternative medicines for the treatment of various types of cancer. Source: https://pubmed.ncbi.nlm.nih.gov/22943501/

Orange

In the following study, the orange peel of 12 varieties of Citrus sinensis from central eastern Sicily was used to obtain essential oils and extracts. Some were extracted by steam distillation, others by extraction in hexane. 54 components were identified in the steam essential oils and 44 in the extracts. In all varieties, the main component is d-limonene (73.9-97%). Antimicrobial activity was investigated against three microorganisms (Staphylococcus aureus, Listeria monocytogens and Pseudomonas aeruginosa) and confirmed for all varieties of orange essential oil. The essential oils 'Sanguinello' and 'Solarino Moro' are significantly active against L. monocytogenes, while 'Valencia' hexane extract is active against all microorganisms tested. Source: https://pubmed.ncbi.nlm.nih.gov/27535797/

The following study aimed to compare the effects of aromatherapy with lavender and orange essential oils on fatigue in dialysis patients. Ninety subjects were randomly divided into three groups of aromatherapy with lavender essential oil, aromatherapy with orange essential oil and control. In each experimental group, the subjects inhaled five drops of lavender essential oil and orange essential oil. Result: The difference in the mean fatigue before and after the intervention was statistically significant in each of the experimental groups, however, this difference was not significant in the control group. That is: aromatherapy with lavender essential oil and orange essential oil can reduce fatigue in hemodialysis patients. Source: https://pubmed.ncbi.nlm.nih.gov/31383445/

The following study showed that orange peel essential oil had a good dose-dependent inhibitory effect on the proliferation of HepG2 liver tumor cells and HCT116 colorectal cancer cells. When the concentration of the essential oil was 0.6 μl/ml or more, the viability rate of both cancer cells became lower than 13%. The Transwell assay showed that the essential oil can inhibit the migration of both cancer cells at a concentration of 0.3 μl/ml. Source: https://pubmed.ncbi.nlm.nih.gov/30704118/

In the following study, an essential oil was prepared by cold pressing orange peel followed by molecular distillation. The anticancer activities of this orange essential oil as well as some of its main constituents were investigated by MTT assays: This orange peel essential oil showed a positive effect on inhibiting the proliferation of a human lung cancer cell line A549 and prostate cancer cell line 22RV-1. Some of the oil constituents showed high anticancer potential and deserved further investigation.Source: https://pubmed.ncbi.nlm.nih.gov/28829378/

peppermint

https://pubmed.ncbi.nlm.nih.gov/18041606/

This study provides further evidence of the influence of essential plant oil aromas on aspects of cognition and mood in healthy participants. One hundred and forty-four volunteers were randomly assigned to the conditions of ylang-ylang aroma, peppermint aroma, or no aroma control.

Peppermint was found to improve memory, while ylang-ylang impaired it and increased processing speed. Regarding subjective mood, peppermint increased alertness and ylang-ylang decreased it, but significantly increased calmness. These results support the claim that the aromas of essential oils can have significant and idiosyncratic effects on both subjective and objective assessments of aspects of human behavior.

In the following study, spearmint and peppermint (Mentha spicata/piperita) essential oils were pre-screened for neurotransmitter receptor binding and acetylcholinesterase (AChE) inhibition. In a double-blind, placebo-controlled, balanced crossover study, 24 participants (mean age 25.2 years) consumed single doses of an encapsulated placebo and 50 µl or 100 µl of the most promising essential oil (peppermint with nicotine/GABAA receptor binding). Psychological functioning was assessed using mood scales and a battery of standardized, cognitively demanding tasks pre-dose and 1, 3, and 6 hours post-dose. Results: The highest dose (100 µl) of the essential oil improved performance on the cognitively demanding Rapid Visual Information Processing Task (RVIP) 1 h and 3 h after dosing, and both doses attenuated fatigue and improved performance on the Serial 3 s Subtraction Task 3 h after dosing. Conclusion: Peppermint (Mentha piperita) essential oil with high menthol/menthone content improves performance on demanding cognitive tasks and attenuates the increase in mental fatigue associated with prolonged cognitive task performance in healthy adults. Future research should consider investigating even higher doses. Source: https://pubmed.ncbi.nlm.nih.gov/30087294/

rosemary

Rosemary essential oil is already used as a preservative in the food industry due to its antioxidant and antimicrobial activity; however, it has been shown to possess additional health benefits. The aim of the following study was to evaluate the protective effect of rosemary essential oil on carbon tetrachloride-induced liver injury in rats and to investigate whether its mechanism of action is associated with modulation of hepatic oxidation status. Rosemary essential oil at the doses of 5 mg/kg and 10 mg/kg was found to exert liver-protective effects by reducing AST and ALT activities by 2-fold in the serum of rats with carbon tetrachloride-induced acute liver injury. Rosemary essential oil prevented the increase in lipid peroxidation induced by carbon tetrachloride. In addition, pretreatment with the essential oil studied for 7 days significantly reversed the activities of the antioxidant enzymes catalase, peroxidase, glutathione peroxidase and glutathione reductase in liver homogenates, especially at a dose of 10 mg/kg. These results show that rosemary essential oil, in addition to its antioxidant capacity, also exerts its liver-protective effects by activating physiological defense mechanisms.Source: https://pubmed.ncbi.nlm.nih.gov/25002023/

sage

https://pubmed.ncbi.nlm.nih.gov/32688401/

Sage is a biennial plant typical of the Mediterranean region and is cultivated mainly for its essential oil, which is widely used in the flavor and fragrance industry and in aromatherapy for its relaxing and immunomodulating effects. In the following study, clary sage essential oil was analyzed and investigated for its effects on pulse, blood pressure and mood in healthy female and male subjects. 32 participants, including 16 women and 18 men, inhaled the sage oil for 30 minutes (pure water as a control). The observed decrease in pulse rate was significantly greater in women than in men (p = 0.026).

tea tree oil

Tea tree oil is an essential oil that is steam distilled from the Australian native plant Melaleuca alternifolia. This essential oil has been used in Australia for nearly 100 years, but is now available worldwide both as a pure oil and as an active ingredient in a range of products. The oil is extracted from the leaves of the tea tree by steam distillation and has a sharp camphor odor followed by a menthol-like cooling sensation.

It has a minimum content of terpinen-4-ol and a maximum content of 1,8-cineole. Terpinen-4-ol is an important component of tea tree oil that exhibits strong antimicrobial and anti-inflammatory properties. Tea tree oil exerts antioxidant activity and has been reported to have broad-spectrum antimicrobial activity against bacterial, viral, fungal and protozoal infections affecting skin and mucous membranes. Several studies have suggested the use of tea tree oil for the treatment of acne vulgaris, seborrheic dermatitis and chronic gingivitis. It also accelerates the wound healing process and exhibits anti-skin cancer activity. This review opens new horizons for dermatologists in the use of this herbal agent. Source: https://pubmed.ncbi.nlm.nih.gov/22998411/

The main uses of tea tree oil have historically benefited from the antiseptic and anti-inflammatory effects of the oil. The following review summarizes recent developments in the antimicrobial and anti-inflammatory activities of the oil and its components, as well as clinical efficacy: https://pubmed.ncbi.nlm.nih.gov/16418522/

For the treatment of acne see also: https://pubmed.ncbi.nlm.nih.gov/25465857/

thyme

Thymol is one of the main components of the essential oils of thyme (Thymus vulgaris L., Lamiaceae), a medicinal plant with multiple therapeutic properties. This plant, native to the Mediterranean region, is widely used as a culinary herb and also has a long history of use for various medicinal purposes. Thymol and thyme today offer multiple functional possibilities in the pharmaceutical, food and cosmetic industries. The interest in formulating pharmaceuticals, nutraceuticals and cosmeceuticals based on thymol is due to several studies that have investigated the potential therapeutic applications of this compound for the treatment of diseases of the respiratory, nervous and cardiovascular systems. In addition, this compound also shows antimicrobial, antioxidant, anticarcinogenic, anti-inflammatory and antispasmodic activities, as well as a potential as an adaptogen (immunomodulator). In the following review, these bioactivities have been covered: https://pubmed.ncbi.nlm.nih.gov/29785774/

Thymol (2-isopropyl-5-methylphenol) belongs to the phenolic monoterpenes and is mainly found in thyme species.It is one of the main components of thyme essential oil. Both thymol and thyme essential oil have long been used in traditional medicine as expectorant, anti-inflammatory, antiviral, antibacterial and antiseptic agents, mainly in the treatment of the upper respiratory tract. New studies have shown their antibiofilm, antifungal, antiviral and anticancer properties. Also, their new therapeutic formulations, such as nanocapsules containing these components, may be useful in medical practice and open up opportunities for their extensive use. The extensive application of thymol and thyme essential oil in healthcare is very promising, but requires further research and analysis. Source: https://pubmed.ncbi.nlm.nih.gov/32917001/

The following study suggests that thyme oil and thymol act as promising antibiofilm agents against drug-resistant strains of Candida species: https://pubmed.ncbi.nlm.nih.gov/32008964/

incense

The resin of the Boswellia species has been used as incense in religious and cultural ceremonies and in medicine since ancient times. Boswellia serrata is a medium to large branched tree of the family Burseraceae (genus Boswellia) that grows in dry mountainous regions of India, North Africa and the Middle East. Oleo-gum resin is taken from the incision on the tree trunk and then kept in a specially made bamboo basket to remove the oil content and solidify the resin. After processing, the gum resin is sorted according to taste, color, shape and size. In India, the states of Andhra Pradesh, Gujarat, Madhya Pradesh, Jharkhand and Chhattisgarh are the main source of Boswellia serrata. The oleo-gum resins contain 30-60% resin, 5-10% essential oils soluble in organic solvents and the rest is polysaccharides. Gum resin extracts of Boswellia serrata have been traditionally used in folk medicine for centuries to treat various chronic inflammatory diseases. The resinous part of Boswellia serrata possesses monoterpenes, diterpenes, triterpenes, tetracyclic triterpenic acids and four major pentacyclic triterpenic acids, i.e. β-boswellic acid, acetyl-β-boswellic acid, 11-keto-β-boswellic acid and acetyl-11-keto-β-boswellic acid, which are responsible for inhibiting pro-inflammatory enzymes. Of these four boswellic acids, acetyl-11-keto-β-boswellic acid is the most potent inhibitor of 5-lipoxygenase, an enzyme responsible for inflammation. Source: https://pubmed.ncbi.nlm.nih.gov/22457547/

Gum resins extracted from trees of the Burseraceae family (Boswellia sp.) are important components of frankincense. Gum resins have been shown to possess anti-inflammatory and antineoplastic effects. Essential oil prepared by distillation of gum resin traditionally used for aromatherapy has also been shown to exhibit tumor cell-specific antiproliferative and proapoptotic activities. The aim of the following study was to optimize the conditions for the production of Boswellea sacra essential oil with the highest biological activity in inducing tumor cell-specific cytotoxicity and suppressing aggressive tumor phenotypes in human breast cancer cells.

Result: In the essential oil of Boswellia sacra produced by hydrodistillation at 100 °C, high molecular weight compounds, including boswellic acids, were more frequently present.All three human breast cancer cell lines were sensitive to essential oil treatment with reduced cell viability and increased cell death, while the immortalized normal human breast cell line was more resistant to essential oil treatment. Boswellia sacra essential oil hydrodistilled at 100 °C was more effective than the essential oil prepared at 78 °C in inducing cancer cell death (T47D cells).

Similar to our previous observations in human bladder cancer cells, Boswellia sacra essential oil induces breast cancer cell-specific cytotoxicity. The suppression of cellular network formation and disruption of spheroid development of breast cancer cells by Boswellia sacra essential oil suggest that the essential oil may be effective in advanced breast cancer. Future preclinical and clinical studies are urgently needed to evaluate the safety and efficacy of Boswellia sacra essential oil as a therapeutic agent for the treatment of breast cancer. Source: https://pubmed.ncbi.nlm.nih.gov/22171782/

Breast cancer is associated with high morbidity and mortality. Chemoresistance and toxicity are the main causes that limit the treatment success in aggressive breast cancer cases. In the following study, the possible effects of frankincense, pine needle and geranium essential oils on breast cancer cell viability, proliferation, migration and invasion and the possible mechanisms were investigated. MCF-7 breast cancer cells were treated with the mentioned essential oils and it was shown that these essential oils suppressed cell viability, proliferation, migration and invasion in human MCF-7 breast cancer cells.

Further data showed that frankincense, pine needle and geranium essential oils induced apoptosis but did not affect cell cycle progression. Consistent with the in vitro activities, frankincense essential oil was effective in inhibiting tumor growth and inducing tumor cell apoptosis in a human breast cancer mouse model. Furthermore, these 3 essential oils modulated the activity of the AMPK/mTOR signaling pathway. In conclusion, the present study demonstrated that frankincense, pine needle and geranium essential oils were involved in BC cell progression possibly via the AMPK/mTOR pathway. Source: https://pubmed.ncbi.nlm.nih.gov/29115548/

Gum resins of Boswellia species, also known as frankincense, are used as a major ingredient in Ayurvedic and Chinese medicine to treat a variety of health problems. Both chemical frankincense extracts and essential oils prepared from gum resins of Boswellia species exhibit antineoplastic activity and have been investigated as potential anticancer agents. The objectives of the following study are to identify optimal conditions for the production of frankincense essential oil that possesses potent antitumor activity and to evaluate the activity in both cultured human pancreatic cancer cells and a mouse cancer model.

Result: Longer duration and higher temperature of hydrodistillation produced higher abundance of high molecular weight compounds, including boswellic acids, in frankincense essential oil fractions. Human pancreatic cancer cells were sensitive to treatment with fractions III and IV (containing higher molecular weight compounds) with suppressed cell viability and increased cell death.All fractions of Boswellia sacra frankincense essential oil are capable of suppressing the viability of a number of human pancreatic cancer cell lines and inducing apoptosis. The effectiveness of tumor cell viability suppressed by essential oil may be associated with the greater abundance of high molecular weight compounds in fractions III and IV. Although the chemical components responsible for tumor cell cytotoxicity remain undefined, essential oil produced by hydrodistillation of Boswellia sacra gum resins could be a useful alternative therapeutic agent for treating patients with pancreatic adenocarcinoma, an aggressive cancer with a poor prognosis. Source: https://pubmed.ncbi.nlm.nih.gov/23237355/

The aim of the following study was to investigate frankincense essential oil for its anti-tumor activity and signaling pathways in bladder cancer cells. Result: Frankincense oil suppressed cell viability in J82 cells of transitional carcinoma of the bladder, but not in the healthy (UROtsa) cells. A comprehensive gene expression analysis confirmed that frankincense oil activates genes responsible for cell cycle arrest, suppression of cell growth and apoptosis in J82 cells. This means that frankincense oil seems to distinguish cancer cells from normal bladder cells and suppresses the viability of cancer cells. Frankincense oil could therefore be an alternative drug to be used within the urinary bladder.  agent for the treatment of bladder cancer. Source: https://pubmed.ncbi.nlm.nih.gov/19296830/

The following study examines the effects of frankincense essential oil and its main components, limonene and α-pinene, on sleep and stress. The effects on plasma levels of corticosterone and glutathione (GSH) as well as on sleep and wake behavior were investigated in sleep-deprived rats. The frankincense essential oil was applied to the skin as a vehicle after dilution in jojoba oil, i.e. applied topically. Frankincense essential oil, at a dilution of 1/1000, significantly reduced corticosterone levels (p < 0.05) and resulted in a significant reduction in plasma glutathione levels. The concentrations of products of oxidative metabolites were reduced by the frankincense. In sleep-deprived rats, frankincense oil enhanced sleep without rapid eye movements. Improvement of sleep and reduction of stress by frankincense essential oil is suggested by this study. Source: https://pubmed.ncbi.nlm.nih.gov/31582666/

Ylang Ylang

Traditionally, ylang-ylang (Cananga odorata) has been used to treat malaria, stomach problems, asthma, gout and rheumatism. Many phytochemical studies have now identified the components contained in the essential oils of ylang ylang, including monoterpenes, sesquiterpenes and phenylpropanoids. Source: https://pubmed.ncbi.nlm.nih.gov/26294929/

Another study (https://pubmed.ncbi.nlm.nih.gov/18041606/) provides further evidence of the influence of essential plant oil aromas on aspects of cognition and mood in healthy participants: One hundred and forty-four volunteers were randomly assigned to the conditions of ylang-ylang aroma, peppermint aroma, or no aroma control. Cognitive performance was assessed using the Cognitive Drug Research computerized assessment battery, completing mood scales before and after the cognitive test. Peppermint was found to improve memory. Regarding subjective mood, peppermint increased alertness and ylang-ylang decreased it, but significantly increased calmness.These results support the claim that essential oil aromas can have significant and idiosyncratic effects on both subjective and objective evaluations of aspects of human behavior.

The following study investigated the biochemical mechanism of the calming effect of Ylang Ylang essential oil in mice: https://pubmed.ncbi.nlm.nih.gov/29545208/ - with the result that ylang ylang essential oil reduced the phosphorylation of ERK1/2 in both PFC and hippocampus. Downregulations of phospho-CREB (p < 0.05) and c-Fos (p < 0.05) were only observed in the hippocampus. The essential oil also affected serotonin metabolism in the brain and reduced corticosterone levels in the blood plasma of m-CPP-treated mice.

cedar

Candida albicans can form biofilms composed of yeast, hyphal and pseudohyphal elements. The following study describes the chemical composition, antibiofilm and antihyphal activities of cedar essential oil, which possesses remarkable antibiofilm activity against Candida albicans but does not affect planktonic cell growth. Nineteen components were identified in cedar essential oil, of which phenols were the major constituents. Of these, camphor, fenchone, fenchyl alcohol, α-thujone and borneol significantly reduced the biofilm formation of Candida albicans. Source: https://pubmed.ncbi.nlm.nih.gov/28824600/

The anti-Helicobacter pylori properties of 26 different commercial essential oils were investigated in vitro in the following study. Nine essential oils with different anti-Helicobacter activities were selected and phytochemical analyses of the selected essential oils were performed by GC-MS method. The phenol red method was used to screen the effect of essential oils on urease activity. The most active essential oils were thyme, lemongrass, cedarwood and lemon balm oils. The most active was cedarwood oil. Source: https://pubmed.ncbi.nlm.nih.gov/32013183/

Swiss stone pine

Breast cancer is associated with high morbidity and mortality. Chemoresistance and toxicity are the main causes that limit the treatment success in aggressive breast cancer cases. In the following study, the possible effects of frankincense, pine needle and geranium essential oils on breast cancer cell viability, proliferation, migration and invasion and the possible mechanisms were investigated. MCF-7 breast cancer cells were treated with the mentioned essential oils and it was shown that these essential oils suppressed cell viability, proliferation, migration and invasion in human MCF-7 breast cancer cells.

Further data showed that frankincense, pine needle and geranium essential oils induced apoptosis but did not affect cell cycle progression. Consistent with the in vitro activities, frankincense essential oil was effective in inhibiting tumor growth and inducing tumor cell apoptosis in a human breast cancer mouse model. Furthermore, these 3 essential oils modulated the activity of the AMPK/mTOR signaling pathway. In conclusion, the present study demonstrated that frankincense, pine needle and geranium essential oils were involved in BC cell progression possibly via the AMPK/mTOR pathway. Source: https://pubmed.ncbi.nlm.nih.gov/29115548/

The following study determined the chemical composition of pine needle (Cedrus deodara) essential oil and evaluated its antioxidant and antimicrobial activity. 23 components representing 95.79% of the oil were identified.The main components include α-terpineol (30.2%), linalool (24.47%), limonene (17.01%), anethole (14.57%), caryophyllene (3.14%) and eugenol (2.14%). Pine needle essential oil showed remarkable antioxidant activity in scavenging free radicals and lipid peroxidation. In addition, the essential oil showed strong antimicrobial activity against typical food-borne microorganisms. Source: https://pubmed.ncbi.nlm.nih.gov/22757704/

The following study investigated the anticancer activity of pine needle (Pinus roxburghii) essential oil and was able to demonstrate cytotoxicity induction in colon, leukemia, multiple myeloma, pancreatic, head, neck and lung cancer cells exposed to this essential oil. Essential oil-induced apoptosis was confirmed by the cleavage of PARP and caspase-3, which suppressed the colony forming ability of tumor cells and 50% inhibition occurred at a dose of 25 μg/ml. Furthermore, essential oil inhibited the activation of the inflammatory transcription factor NF-κB and the expression of NF-κB-regulated gene products associated with cell survival (survivin, c-FLIP, Bcl-2, Bcl-xL, c-Myc, c-IAP2), proliferation (cyclin D1) and metastasis (MMP-9). The study concludes that pine needle essential oil possesses considerable anticancer activity and could be used as an anticancer agent, which requires further investigation to identify the bioactive compounds followed by in vivo studies. Source: https://pubmed.ncbi.nlm.nih.gov/29743861/

The following study sheds light on the effect of pine needle oil in the treatment of Alzheimer's disease/dementia. The most common neurodegenerative disease is Alzheimer's disease. It is determined by the deposits of amyloid beta peptide, which leads to memory impairment, oxidative stress and neurodegeneration. Aromatherapy with essential oils could be a natural treatment option for Alzheimer's disease. Therefore, this study aimed to identify the neuroprotective and beneficial effects on the central nervous system of pine needle (Pinus halepensis) essential oil in a rat model of acute amyloid beta toxicity. The results suggest that Pinus halepensis pine needle essential oil has beneficial effects on the central nervous system as well as neuroprotective effects and can be considered as a therapeutic tool to attenuate Aβ toxicity and neuronal dysfunction. Source: https://pubmed.ncbi.nlm.nih.gov/30784941/

In the following article, the anti-tumor activity of Korean pine (Pinus koraiensis) pine needle essential oil on metastatic gastric cancer cells (MGC-803 cell line) and its mechanism were investigated. In vitro anti-tumor experiments showed that the oil could significantly inhibit the proliferation and migration of MGC-803 cells, and also arrest the cell cycle in G2/M phase, reduce mitochondrial membrane potential and induce apoptosis. The results showed that Korean pine needle essential oil can exert anti-tumor activity via the HIPPO/YAP signaling pathway. The anti-tumor mechanism of this oil should be further investigated. Source: https://pubmed.ncbi.nlm.nih.gov/31731517/

lemon

COVID-19 has been declared the most serious health emergency in modern history worldwide. The angiotensin-converting enzyme 2 (ACE2) receptor, a host cell receptor, has been found to play a crucial role in viral cell entry. Therefore, ACE2 blockers may be a potential target for antiviral intervention. The following study investigated the ACE2 inhibitory effect of 10 essential oils.Among them, geranium and lemon oils showed significant ACE2 inhibitory effects in epithelial cells. In addition, immunoblotting and qPCR analysis also confirmed that geranium and lemon oil possess strong ACE2 inhibitory effects. The results suggest that geranium and lemon essential oils and their derived compounds are valuable natural antiviral agents that can help prevent SARS-CoV-2/COVID-19 from entering the human body. Source: https://pubmed.ncbi.nlm.nih.gov/32575476/