Aromatic Scholars

Sprout: Mechanisms of Action

This lesson will explore the mechanisms by which essential oils interact with and influence the central nervous system (CNS), autonomic nervous system (ANS), endocrine system, and immune system, focusing on their effects related to stress and mental health.

Absorption and Transport of Essential Oils

Before discussing the specific effects of EOs on various body systems, it’s important to understand how these compounds are absorbed and transported to their sites of action, particularly the brain. Essential oils (EOs) can enter the body through multiple routes, including inhalation, topical application, and oral administration.

1. Inhalation Route:

Inhalation is a primary method of EO administration, utilizing two main pathways. The first is through the olfactory system, where EO molecules interact with olfactory receptors in the nasal cavity. This triggers electrical signals that are transmitted directly to the olfactory bulb and then to various brain regions, including the limbic system, allowing for rapid effects on mood and emotion.1 The second inhalation pathway is via the respiratory system, where inhaled EO molecules can be absorbed through the respiratory tract, passing into the alveoli and then into the bloodstream. From there, lipophilic components can cross the blood-brain barrier (BBB) to directly affect the central nervous system (CNS).

2. Topical Application:

The topical application presents another route of administration, where some essential oil components can be absorbed transdermally. Lipophilic molecules can enter the bloodstream and, if they can cross the BBB, reach the brain.

3. Oral Administration:

While less common, oral administration is another potential route, where essential oils are absorbed through the gastrointestinal tract and enter the bloodstream. Again, lipophilic components that can cross the BBB may directly affect the CNS.3

Some lipophilic components of essential oils may be able to cross the blood-brain barrier (BBB), allowing for direct effects on the central nervous system (CNS). The ability of essential oils to affect the CNS through multiple pathways, including direct olfactory signaling and potential BBB penetration, contributes to their complex effects on mood and mental health.

Central Nervous System (CNS) Effects

EOs can influence CNS function through several mechanisms:

1. Neurotransmitter Modulation:
Many essential oils may alter levels of key neurotransmitters involved in mood regulation and stress responses.

Serotonin (5-HT): Lavender (Lavandula angustifolia) , ylang-ylang (Cananga odorata), lemon (Citrus limon) and bergamot (Citrus bergamia) essential oils have been shown to increase 5-HT levels or interact with the serotonergic system in animal studies.
Dopamine (DA): Ylang-ylang essential oil has been found to affect dopamine levels in the striatum in mice.
GABA: Lavender and bergamot essential oils have demonstrated interactions with the GABAergic system, possibly contributing to their anxiolytic and sedative effects.

2. Neurotrophic Factor Regulation:
EOs can influence the expression of neurotrophic factors, particularly Brain-Derived Neurotrophic Factor (BDNF):

Lavender (Lavandula angustifolia) essential oil has been shown to prevent the decrease in serum BDNF levels typically seen in corticosterone-induced depression in rats.

3. Neurogenesis and Neuroplasticity:
Some EOs promote the growth of new neurons and enhance neuronal plasticity:

Lavender essential oil has been shown to increase neurogenesis and enhance dendritic complexity in the hippocampus of rats.
D-limonene, a component of many citrus essential oils, has been found to promote neurite outgrowth in cell culture studies through activation of the p38 MAPK pathway.

4. Direct Receptor Interactions:
Some EO components can directly interact with neuronal receptors:

β-caryophyllene, found in many EOs, can interact with CB2 receptors of the endocannabinoid system, potentially contributing to anti-inflammatory and mood-regulating effects.

5. Olfactory Signaling:
We will be covering this in-depth in Part 3.

Autonomic Nervous System (ANS) Effects

Many of the stress-reducing effects of EOs are mediated through modulation of ANS activity:

1. Parasympathetic Activation:
Many essential oils enhance parasympathetic nervous system activity, promoting relaxation:

Lavender (Lavandula angustifolia) essential oil has been shown to decrease heart rate and blood pressure, indicative of increased parasympathetic tone.
Bergamot (Citrus bergamia) essential oil has demonstrated similar effects, increasing parasympathetic nervous system activity as measured by heart rate variability.

2. Sympathetic Inhibition:
Many essential oils reduce sympathetic nervous system activity, which is often overactive during stress and anxiety:

Ylang-ylang (Cananga odorata) essential oil has been found to decrease heart rate and blood pressure in healthy men, suggesting a reduction in sympathetic tone.
Yuzu (Citrus junos) essential oil demonstrated decreased sympathetic nervous system activity in premenstrual women.

3. ANS Balance:
Many EOs appear to promote overall balance between the sympathetic and parasympathetic branches of the ANS:

Petitgrain (Citrus aurantium var. amara) essential oil was found to improve autonomic balance in office workers and was associated with enhanced workplace performance and reduced stress levels.

Endocrine System Effects

The endocrine system, particularly the hypothalamic-pituitary-adrenal (HPA) axis, is also influenced by EOs:

1. Cortisol Regulation:
Some essential oils have been shown to modulate cortisol levels, a primary stress hormone:

Lavender (Lavandula angustifolia) , and bergamot (Citrus bergamia) essential oils have consistently demonstrated cortisol-lowering effects in human studies.

2. HPA Axis Modulation:
Some EOs appear to influence the overall functioning of the HPA axis:

Frankincense (Boswellia sp.) essential oil has been shown to attenuate stress-induced elevations in corticosterone (the rodent equivalent of cortisol) in rats.
Asarum (wild ginger: Asarum heterotropoides) essential oil has been reported to increase corticotropin-releasing hormone (CRH) levels in the hypothalamus of mice, suggesting that different essential oils may have distinct effects on the HPA axis.

Breathing and Emotion:

Respiration is closely linked to emotional states, with stress often leading to altered breathing patterns.

Some essential oils, like lavender (Lavandula angustifolia), have been shown to decrease respiratory rate during panic attacks, potentially contributing to their calming effects.

Summary

Essential oils exert their effects on mental health and stress responses through complex interactions with the central nervous system, autonomic nervous system, endocrine system, and, to some extent, the immune system. These effects are mediated through various mechanisms, including neurotransmitter modulation, regulation of neurotrophic factors, promotion of neurogenesis, direct olfactory signaling, modulation of autonomic nervous system activity, regulation of the HPA axis, and reduction of inflammation and oxidative stress. The unique properties of essential oils, particularly their ability to be absorbed through both olfactory and respiratory routes, allow for rapid and multifaceted effects on the nervous system. This complexity of action may explain why essential oils can have broad effects on mood, stress, and mental health.

Sprout: Forest Bathing

Forest Bathing: Reconnecting with Nature
Improving health and emotional well-being

Spending time in nature has always been a source of relaxation, rejuvenation, and healing for humans. However, in recent decades, as more people live in urban areas and spend increasing amounts of time indoors, many have become disconnected from the natural world. A practice called “Shinrin-yoku,” which translates to “forest bathing” or “absorbing the forest atmosphere,” aims to counter this trend and restore our relationship with nature.

The Origins and Concept of Forest Bathing

Forest bathing emerged in Japan in the 1980s as a way to promote well-being and decrease stress in the population. It doesn’t involve exercising, hiking, or literally bathing. Instead, Shinrin-yoku is simply being immersed in nature, connecting with it through our senses of sight, hearing, smell, taste, and touch. By opening our senses, we bridge the gap between us and the natural world.

Enjoying Shinrin-yoku through all five senses

Sense of sight: green color, yellow color, red color, forest landscape, etc.
Sense of smell: aromas from trees and flowers, phytoncides, unique forest aromas (e.g., soil, moisture, etc.).
Sense of hearing: forest sounds, listening to the birds singing, and the breeze rustling in the leaves of the trees.
Sense of touch: touching trees puts your whole body in the forest atmosphere.
Sense of taste: eating foods and fruits from forests, tasting the fresh air in forests.

In Japanese, “shinrin” means forest, and “yoku” refers to bathing, atmosphere, or immersion. Thus, Shinrin-yoku literally translates to “forest bathing” or “taking in the forest atmosphere.” This practice is based on the idea that humans have an innate connection to nature, a concept known as the Biophilia Hypothesis proposed by E.O. Wilson.

The concept is that by mindfully spending time in a forest environment, away from the stresses of daily life, we can heal our minds and body. Over the past several decades, a significant amount of research, particularly in Japan and South Korea, has demonstrated a wide array of health benefits from practicing forest bathing. Let’s explore what this research shows and how to experience the benefits yourself.

Mental Health Benefits of Forest Bathing

Some of the most well-established benefits of Shinrin-yoku relate to psychological well-being. Multiple studies have found forest bathing can:

Reduced stress and anxiety: Multiple studies have reported decreased levels of stress and anxiety and increased feelings of calmness and relaxation following forest bathing experiences.
Improved mood: Participants in forest bathing studies often report improved mood states, including decreased feelings of depression and increased feelings of vigor.
Enhanced cognitive function: Research has suggested that exposure to natural environments can improve attention and cognitive performance.
Decreased rumination: One study found that walking in nature, compared to an urban environment, led to decreased activity in the subgenual prefrontal cortex, an area of the brain linked to rumination – a risk factor for depression.
Enhance recovery from mental fatigue and improve sleep
Boost vigor and decrease feelings of anger, confusion, and depression

In one study, participants who walked in a forest reported significant decreases in measures of hostility, depression, and anxiety compared to those who walked in an urban setting. Even just viewing a forest scene for 20 minutes reduced stress and improved mood compared to viewing urban scenes.

Brain imagining shows forest environments can lower activity in the prefrontal cortex, the brain region active during rumination. Spending time in nature gives this overactive region a much-needed break, resulting in mental relaxation. At the same time, natural scenes activate the parasympathetic nervous system, which promotes relaxation and decreases sympathetic nervous system activity, which triggers stress and anxiety.

Forest therapy has even been shown to help people dealing with more serious psychological issues. Alcoholics who participated in a forest therapy camp showed significant improvements in depression compared to those who didn’t attend. In another study, a forest therapy program improved mood and reduced anxiety in patients with chronic stroke.

Forest therapy also boosts cognitive function. Spending time in nature has been shown to improve focus, concentration, and memory. It can provide mental restoration and reduce mental fatigue from sustained attention to cognitively demanding tasks.

What makes nature so psychologically healing? The Biophilia Hypothesis proposes that since humans evolved in nature, we have an innate affinity towards natural environments. We feel a sense of belonging and ease in nature that promotes relaxation and restoration. The Attention Restoration Theory suggests that natural environments capture our attention modestly and don’t require directed attention, giving our overloaded minds a chance to rest and recover. Whatever the mechanism, forest bathing provides a simple way to care for our psychological well-being. But the benefits extend to the body as well.

Physical Health Benefits of Shinrin-Yoku

Spending mindful time in forests has been shown to have significant positive effects on the body. Some of the research-backed physical health benefits include:

Lower heart rate, blood pressure, and stress hormones like cortisol and adrenaline
Increased parasympathetic nervous system activity, which promotes relaxation
Enhanced immune system functioning and anti-cancer protein production
Decreased blood glucose levels and improved insulin sensitivity
Reduced inflammation and oxidative stress
Improved cardiovascular health and decreased risk of heart disease and stroke
Better respiratory health and lung function

Many of these effects can be attributed to phytoncides, the natural oils emitted by trees and plants. Inhaling phytoncides increases immune function by boosting natural killer (NK) cell activity. NK cells can destroy tumor- and virus-infected cells. In one study, a 3-day forest bathing trip increased NK cell activity by 50%, and the effects lasted for over 30 days.

The act of breathing in the fresh forest air, with its rich oxygen levels and phytoncides, influences our nervous system. Inhaling phytoncides reduces stress hormones, decreases sympathetic nervous system activity (our fight-or-flight response), and increases parasympathetic activity (our rest-and-digest state). This results in lower blood pressure, reduced anxiety, and a general feeling of relaxation.

Even touching or viewing real plants and trees has a relaxing effect. In one experiment, people who touched tree bark had lower blood pressure than those who touched metal or fabric. Viewing real flowers or a kiwifruit orchard scene led to increased parasympathetic activity and a feeling of relaxation, more so than viewing artificial flowers or urban scenes.

Some specific patient populations have experienced notable benefits from forest therapy:

Elderly patients with chronic heart failure experienced reduced inflammatory responses and improved heart health after a 4-day forest bathing trip.
Patients with chronic stroke saw improvements in depression, anxiety and pain after a forest therapy program.
Elderly patients with high blood pressure had reduced hypertension and improved mood following a 7-day forest therapy session. ,
Patients with chronic obstructive pulmonary disease (COPD) had decreases in inflammation and subjective feelings of exertion after a forest bathing trip.

The research paints a clear picture: Mindful time in nature can be a powerful preventive medicine and healing tool for a variety of physical and mental ailments. Best of all, it’s free, has no negative side effects, and is accessible to most people. Even viewing nature scenes or having plants in your home or office can provide benefits.

Bringing Forest Bathing into Your Life

Hopefully, the evidence for Shinrin-yoku has inspired you to experience it yourself! While you may not be able to spend hours in a pristine forest every day, you can still find ways to connect with nature:

Find a park, botanical garden, hiking trail, or another natural area near your home or workplace and spend time there regularly.
Practice mindfulness in your own garden, backyard, or any spot with trees and greenery.
Bring nature into your indoor environment with houseplants, a water fountain, nature photography, or essential oils from trees like cedar or pine.
Listen to recordings of nature sounds, like birds singing or water flowing, to destress.
View nature scenes on your computer, TV, or in artwork to get a dose of greenery.

With a bit of creativity, you can experience the healing power of nature wherever you are. As our modern lifestyles keep us increasingly plugged in and stressed out, the practice of forest bathing can be a much-needed respite for restoration. By immersing our senses mindfully in nature, we nourish our mind, body and soul.

Utilizing Essential Oils

Essential oils derived from trees such as pine (Pinus sp.), spruce (Picea sp.), cypress (Cupressus sempervirens), and fir (Abies sp.) contain many of the same compounds found in forest air. Using essential oils may provide some of the benefits of forest bathing and could be a helpful complementary practice, especially for those unable to access forests regularly. Inhaling or diffusing forest tree essential oils can be incredibly beneficial for reducing stress and anxiety and building resiliency against everyday stressors.

It is important to note that forest bathing involves more than just exposure to phytoncides. The practice engages all five senses and involves being physically present in a natural environment. For instance, the Attention Restoration Theory and Stress Reduction Theory emphasize the visual and experiential aspects of being in nature, which cannot be fully replicated by essential oils alone.

Forest Bathing in Different Landscapes

While the term “forest bathing” implies the need for a forest, research has shown that various natural environments can provide similar benefits. One study found that urban parks and even street trees can offer some of the same stress-reducing effects as forests.

Water features in natural settings have also been shown to enhance the restorative effects of nature. Another study compared the effects of viewing purely vegetated landscapes versus landscapes with water features. While both types of landscapes provided benefits, water landscapes showed a slightly higher impact on physical and mental health, although the difference was not statistically significant.

This research suggests that people living in urban areas without easy access to forests can still benefit from nature exposure in city parks, gardens, or even by viewing nature scenes through windows or in photographs.

How to Practice Shinrin-Yoku

The beauty of forest bathing is its simplicity. Here are the basic steps:

Find a location. Ideally, this should be a forest with minimal noise and distractions, but any natural area with trees can work. Popular sites are often “healing forests” that have been officially designated for Shinrin-yoku.
Leave behind your phone, camera, and any other distractions. The goal is to be fully present in nature without the need to “do” anything.
Walk slowly and aimlessly through the forest. There’s no need to hike or follow a specific trail. Let your body guide you.
Take long, deep breaths. Inhale the fresh air and forest aromas. Notice the oxygen flowing through your body.
Stop and engage your senses. Notice the sunlight filtering through the trees, the texture of the tree bark, the sound of birds singing or a stream flowing, the fragrance of the forest, or the taste of the air.
If possible, continue this slow, mindful walking for about two hours. Find a scenic spot to sit, relax your mind, and take in the forest’s restorative power.

The next time you feel anxious, depressed, or fatigued or want to enhance your health and well-being, try taking a “bath” in the forest. Breathe in the fresh air, listen to the rustle of the leaves, and feel the sun on your skin and the earth beneath your feet. Allow nature to wash over you and experience the healing power of the forest. Your mind and body will thank you.

Lesson 6b: Essential Oils and the Immune System

The Potential Role of Essential Oils in Supporting the Immune System

Several in vitro studies have examined how isolated immune cells respond when directly exposed to various essential oils. While these simplified models can’t fully predict effects within the body’s complex environment, they provide mechanistic clues and have yielded some intriguing findings:

Phagocytosis: Phagocytes, like macrophages, are key innate immune cells that engulf and destroy pathogens. Exposure to eucalyptus essential oil (Eucalyptus globulus) was found to dramatically stimulate the phagocytic activity of human macrophages in culture, even more so than lipopolysaccharide, a known immune stimulant. In some studies, Clove oil (Syzygium aromaticum) and its component eugenol also enhanced phagocytosis.

Cytokine production: Cytokines are signaling molecules that immune cells use to communicate and coordinate responses. Some essential oils like lavender (Lavandula angustifolia), tea tree (Melaleuca alternifolia), and their constituents were found to modulate the production of various pro- and anti-inflammatory cytokines by cultured immune cells. The overall effect seems to be balancing – stimulating defenses while restraining excessive inflammation.

Expression of surface receptors: Some studies found essential oils increased the expression of receptors on immune cells that mediate phagocytosis, cell adhesion, and activation status – all markers of enhanced immune readiness.

Specific Essential Oils and Their Immunomodulatory Effects

1. Eucalyptus (Eucalyptus globulus) essential oil:
In various studies, eucalyptus oil, particularly its main component, 1,8-cineole (eucalyptol), has shown significant immunomodulatory effects. In vitro experiments demonstrated that eucalyptus oil dramatically stimulated the phagocytic activity of human monocyte-derived macrophages (MDMs). This effect was even more pronounced than that observed with lipopolysaccharide, a known immune stimulant.

In vivo studies in rats showed that oral administration of eucalyptus oil enhanced the phagocytic activity of peripheral blood monocytes and granulocytes in immunocompetent animals. Interestingly, eucalyptus oil also helped restore immune function in rats immunosuppressed by the chemotherapy drug 5-fluorouracil. This suggests potential applications in managing immunosuppression caused by cancer treatments. ,

2. Clove (Syzygium aromaticum) essential oil:
Clove oil and its major constituent eugenol have demonstrated complex immunomodulatory effects. Some studies found that clove oil enhanced the phagocytic activity of macrophages and increased antibody production in animal models. However, other research has shown immunosuppressive effects, highlighting the nuanced nature of essential oil interactions with the immune system.

3. Tea Tree (Melaleuca alternifolia) essential oil:
Tea tree oil, particularly its main component terpinen-4-ol, has been reported to suppress the production of inflammatory cytokines by activated human monocytes in vitro. It has also been shown to enhance the phagocytic activity of macrophages. These findings suggest a potential role for tea tree oil in balancing immune responses.

4. Lavender (Lavandula angustifolia) essential oil:
In vitro studies have shown that lavender essential oil treatment increased the phagocytic activity of human MDMs while simultaneously reducing the production of inflammatory cytokines. This dual action suggests a potential for lavender oil to enhance immune defenses while mitigating excessive inflammation.

In a clinical study, aromatherapy massage with lavender oil increased levels of salivary IgA, an antibody important for mucosal immunity. This provides some preliminary evidence for immune-enhancing effects in humans.

5. Ginger (Zingiber officinale) essential oil:
Animal studies have shown that ginger essential oil can increase the phagocytic activity of peripheral blood monocytes and granulocytes in treated rats.

Other Essential Oils with Potential Immunomodulatory Effects:

Thyme (Thymus vulgaris)
Oregano (Origanum vulgare)
Lemon (Citrus limon)
Peppermint (Mentha x piperita)

Specific Components of Essential Oils

Several individual compounds found in essential oils have been investigated for their immune effects:

α-pinene and limonene: Found in many citrus oils, these compounds have shown potential to modulate immune responses in some studies. ,
Menthol: The primary component of peppermint essential oil, menthol, has been studied for its effects on inflammatory processes. ,
Carvacrol: A major constituent of oregano essential oil, carvacrol has demonstrated antimicrobial and immunomodulatory properties in various studies. ,
Thymol: Found in high concentrations in thyme essential oil, thymol has been investigated for its effects on immune cell function.
Cinnamaldehyde: The compound responsible for cinnamon bark’s characteristic aroma, cinnamaldehyde has shown the potential to influence immune responses in some research. ,

Animal Studies: Effects on Systemic Immunity

Research has also explored the immunomodulatory effects of essential oils when administered to live animals, either orally or by inhalation. Though not always predictive of human responses, animal models provide a more realistic glimpse at systemic effects.

Rodent studies found that oral intake of essential oils such as eucalyptus and ginger enhanced the activity of circulating phagocytes like monocytes and granulocytes. Some essential oils also boosted overall white blood cell counts, antibody production, and delayed-type hypersensitivity skin responses – all suggesting a general tonic effect on immune defenses. Eucalyptus oil intake helped restore the numbers and function of immune cells suppressed by chemotherapy drugs in rat models. This points to potential applications in managing immunosuppression.

Studies in livestock and fish found that dietary supplementation with essential oils like oregano, thyme, and cinnamon enhanced various immune parameters. While not directly applicable to humans, these findings hold relevance for veterinary and agricultural practices.

Human Trials: A Mixed Picture

Despite the promising preclinical findings, clinical evidence for the immune benefits of essential oils in humans remains limited and mixed. A few studies have linked aromatherapy with some changes in immune cell numbers, activation, or salivary antibodies. However, others found no significant effects on measured immune markers.

One notable area of human research is the immune impact of shinrin-yoku, or “forest bathing,” the practice of immersing oneself in nature. Airborne essential oil compounds emitted by trees are considered to be one of the potential mechanisms behind the increased natural killer cell activity and anti-cancer proteins observed in forest bathing studies. , However, other factors like phytoncides and stress reduction likely also play a role.

Proposed Mechanisms of Action

While more research is needed to clarify the immunological effects and underlying mechanisms, some potential ways essential oils may modulate immunity include:

Direct interaction with cellular receptors involved in immune signaling pathways
Modulating production and activity of enzymes that synthesize immune mediators
Antioxidant and anti-inflammatory properties that protect immune cells from damage
Acting on the nervous and endocrine systems which in turn influence immunity
Antimicrobial effects that reduce the burden on the immune system

It’s important to note that different essential oils contain diverse bioactive compounds that may act through distinct mechanisms. Additionally, the concentration, route, and duration of exposure can influence the nature and magnitude of immunological effects.

Stress, the Immune System and Aromatics

Stress profoundly impacts the immune system through complex interactions between the nervous, endocrine, and immune systems, a field of study known as psychoneuroimmunology. When we experience chronic stress, our adrenal glands release hormones like cortisol, which can suppress T cell and neutrophil activity, reduce antibody production, and increase inflammation.

Stress-induced immunosuppression makes us more susceptible to infections and various immune-related conditions. However, there are natural ways to mitigate these effects. For example, utilizing essential oils to reduce stress can support immunity by helping to calm the nervous system and regulate the body’s stress response. Like mindfulness practices such as meditation and yoga, which have been shown to enhance multiple facets of immunity, aromatherapy can help reduce the impact of chronic stress and its negative impact on immune function.

Summary

The interface between essential oils and the immune system is a fascinating area of ongoing research. While compelling hints of immunomodulatory potential exist, more human clinical studies are needed to translate the preclinical findings into clear guidelines for therapeutic use.

As always, a holistic approach incorporating a healthy lifestyle, diet and stress management remains the bedrock of immune health.

Live Stream 2021: Introductions and Cultivating Relationships

Saturday:

Part 1

Part 2

Part 3

Sunday:

Part 1

Part 2

Part 3

Slide Presentation PDF

Live Stream 2021 Class

Week Two

Click here for Zoom Recording: USE PASSWORD: Md3nOZ.y

Jade’s slides PDF

Presentation Slides PDF (3 slides per page)

Presentation Slides PDF (1 slide per page)

Please note, we started the recording a few minutes into the session, my apologies.

Aromatic Scholars Module 1: Introduction

Research Class 2023

Class Recordings

Research Reviews and Terms

Class 3 Part 1: Discussions

Class 3 Part 2: Research on EO’s and Mental Health

Class 3 Part 3: Research and Discussions

Class 2 Part 4: Discussions

Class 2 Part 5: Research Brief and Close of Session

Research Papers

Bagheri-Nesami M, Shorofi S A, Nikkhah A, Espahbodi F. (2017). The effects of lavender essential oil aromatherapy on anxiety and depression in haemodialysis patients. Pharmaceutical and Biomedical Research, 3(1) :8-13 URL: http://pbr.mazums.ac.ir/article-1-138-en.html

Braden, R., Reichow, S., & Halm, M. A. (2009). The use of the essential oil lavandin to reduce preoperative anxiety in surgical patients. Journal of Perianesthesia Nursing, 24(6), 348–355. https://doi.org/10.1016/j.jopan.2009.10.002

Ebrahimi, H., Mardani, A., Basirinezhad, M. H., Hamidzadeh, A., & Eskandari, F. (2022). The effects of Lavender and Chamomile essential oil inhalation aromatherapy on depression, anxiety and stress in older community-dwelling people: A randomized controlled trial. Explore (New York, N.Y.), 18(3), 272–278. https://doi.org/10.1016/j.explore.2020.12.012

Erna Amin, Bambang Rahardjo, Kusworini. (2020). Aromatherapy oils of lavender (Lavandula angustifolia) inhalance reduced norepinephrine levels of woman with postpartum blues based on Edinburgh postpartum depression scale. AIP Conf. Proc., 2231(1): 040065. https://doi.org/10.1063/5.0003654

Farzaneh M, Zarean V, Abbasijahromi A, Mohit M, Amirkhani M, et al. (2022). A randomized controlled trial examining the effect of aromatherapy using the damask rose essential oil on pre-operative anxiety levels. Nephro-Urology Monthly, 14(2):e116696 https://doi.org/10.5812/numonthly.116696.

Chandharakool, S., Koomhin, P., Sinlapasorn, J., Suanjan, S., Phungsai, J., Suttipromma, N., Songsamoe, S., Matan, N., & Sattayakhom, A. (2020). Effects of tangerine essential oil on brain waves, moods, and sleep onset latency. Molecules (Basel, Switzerland), 25(20), 4865. https://doi.org/10.3390/molecules25204865

Chang, K. M., & Shen, C. W. (2011). Aromatherapy benefits autonomic nervous system regulation for elementary school faculty in Taiwan. Evidence-based Complementary and Alternative medicine: eCAM, 2011, 946537. https://doi.org/10.1155/2011/946537

Chung, Y. H., Chen, S. J., Lee, C. L., Wu, C. W., & Chang, Y. S. (2022). Relaxing effects of breathing Pseudotsuga menziesii and Lavandula angustifolia essential oils on psychophysiological status in older adults. International Journal of Environmental Research and Public Health, 19(22), 15251. https://doi.org/10.3390/ijerph192215251

Effati-Daryani, F., Mohammad-Alizadeh-Charandabi, S., Mirghafourvand, M., Taghizadeh, M., & Mohammadi, A. (2015). Effect of lavender cream with or without foot-bath on anxiety, stress and depression in pregnancy: a randomized placebo-controlled trial. Journal of Caring Sciences, 4(1), 63–73. https://doi.org/10.5681/jcs.2015.007

Hongratanaworakit T. (2009). Relaxing effect of rose oil on humans. Natural Product Communications, 4(2), 291–296.

Hongratanaworakit, T., & Buchbauer, G. (2004). Evaluation of the harmonizing effect of ylang-ylang oil on humans after inhalation. Planta Medica, 70(7), 632–636. https://doi.org/10.1055/s-2004-827186

Hung, C. L., Lin, Y. L., Chou, C. M., & Wang, C. J. (2023). Efficacy of aromatherapy at relieving the work-related stress of nursing staff from various hospital departments during COVID-19. Healthcare (Basel, Switzerland), 11(2), 157. https://doi.org/10.3390/healthcare11020157

Karimzadeh, Z., Azizzadeh Forouzi, M., Rahiminezhad, E., Ahmadinejad, M., & Dehghan, M. (2021). The effects of lavender and Citrus aurantium on anxiety and agitation of the conscious patients in intensive care units: a parallel randomized placebo-controlled trial. BioMed Research International, 2021, 5565956. https://doi.org/10.1155/2021/5565956

Kim, C., Lee, G., & Song, C. (2023). The effect of short-term inhalation of fir essential oil on autonomic nervous activity in middle-aged women. Explore (New York, N.Y.), S1550-8307(23)00104-0. Advance online publication. https://doi.org/10.1016/j.explore.2023.04.006

Lehrner, J., Marwinski, G., Lehr, S., Johren, P., & Deecke, L. (2005). Ambient odors of orange and lavender reduce anxiety and improve mood in a dental office. Physiology & Behavior, 86(1-2), 92–95. https://doi.org/10.1016/j.physbeh.2005.06.031

Lotfi, A., Shiri, H., Ilkhani, R., Sefidkar, R., and Esmaeeli, R. (2019). The efficacy of aromatherapy With Melissa officinalis in reducing anxiety in cardiac patients: a randomized clinical trial. Crescent Journal of Medical and Biological Sciences, 6(3), 293–299. eISSN 2148-9696

Mahdood, B., Imani, B., & Khazaei, S. (2022). Effects of inhalation aromatherapy With Rosa damascena (Damask rose) on the state anxiety and sleep quality of operating room personnel during the COVID-19 pandemic: A randomized controlled trial. Journal of Perianesthesia Nursing: Official Journal of the American Society of PeriAnesthesia Nurses, 37(4), 493–500. https://doi.org/10.1016/j.jopan.2021.09.011

Matsumoto, T., Asakura, H., & Hayashi, T. (2014). Effects of olfactory stimulation from the fragrance of the Japanese citrus fruit yuzu (Citrus junos Sieb. ex Tanaka) on mood states and salivary chromogranin A as an endocrinologic stress marker. Journal of Alternative and Complementary Medicine, 20(6), 500–506.

Rambod, M., Rakhshan, M., Tohidinik, S., & Nikoo, M. H. (2020). The effect of lemon inhalation aromatherapy on blood pressure, electrocardiogram changes, and anxiety in acute myocardial infarction patients: A clinical, multi-centered, assessor-blinded trial design. Complementary therapies in clinical practice, 39, 101155. https://doi.org/10.1016/j.ctcp.2020.101155

Rashidi-Fakari, F., Tabatabaeichehr, M., & Mortazavi, H. (2015). The effect of aromatherapy by essential oil of orange on anxiety during labor: A randomized clinical trial. Iranian Journal of Nursing and Midwifery Research, 20(6), 661–664. https://doi.org/10.4103/1735-9066.170001

Seong Park, D. (2017). Effects of juniper essential oil on the activity of autonomic nervous system. Biomedical Science Letters, 23(3):286-289 DOI:10.15616/BSL.2017.23.3.286

Scandurra, C., Mezzalira, S., Cutillo, S., Zapparella, R., Statti, G., Maldonato, N. M., Locci, M., & Bochicchio, V. (2022). The effectiveness of neroli essential oil in relieving anxiety and perceived pain in women during labor: A Randomized Controlled Trial. Healthcare (Basel, Switzerland), 10(2), 366. https://doi.org/10.3390/healthcare10020366

Watanabe, E., Kuchta, K., Kimura, M., Rauwald, H. W., Kamei, T., & Imanishi, J. (2015). Effects of bergamot ( Citrus bergamia (Risso) Wright & Arn.) essential oil aromatherapy on mood states, parasympathetic nervous system activity, and salivary cortisol levels in 41 healthy females. Forschende Komplementarmedizin, 22(1), 43–49. https://doi.org/10.1159/000380989