By Amanda Lattin, BA, MAT, Dip. Aroma., MH, RA
There are two primary questions the aromatherapist is faced with for each formula they create: which essential oils will be the most effective and safe for the situation and what will be the most effective and safe administration method to use with the chosen essential oils?
In evaluating the many options for answering these two questions, the aromatherapist draws on their education, experience, and skill. When deciding which administration method to use, topical application or oral administration may be perceived as being more impactful due to the more obvious interaction with the body and body systems. Indeed, there is a heavy influence in society and medical culture to feel medicine must be ingested or applied to the body to be effective or impactful. And, these administration methods have their useful and safe roles. However, there is another administration method which is in many ways unique to aromatherapy, and perhaps most closely mimics how one would experience essential oils in nature – inhalation.
Experiencing aromatherapy via essential oil inhalation is simple, almost effortless, and very non-invasive; yet, the subtle nature of essential oil inhalation can lead to questions about its viability as an effective method of administration. Thankfully, there are several areas where essential oil inhalation has been studied in research with promising results.
Improving Quality of Sleep
Difficulty falling asleep, staying asleep, and poor-quality sleep are issues many people face. This is an area where aromatherapy can provide support. Several recent research studies have evaluated the effectiveness of essential oil inhalations for improved quality of sleep in specific groups.
Improved sleep was seen in nurses following night-shift work after a three-minute lavender Lavandula angustifolia (L.) essential oil inhalation and use of an aroma stone beside the bed for three days. (1) Intensive care unit patients saw improved quality of sleep and lowered anxiety after daily inhalation of a 2% lavender solution for 15 days. (2) Another study, which focused on the effects of aromatherapy for only one night, also found improved sleep quality and lowered blood pressure in intermediate care hospital patients who had a 3ml vial of lavender L. angustifolia essential oil placed beside their bed from 10pm until 6am. (4)
Patients diagnosed with cancer experience anxiety and stress, which can often interfere with sleep. A patient survey gave out 65 aromasticks (personal inhalers) over a 13-week period to cancer patients at a cancer center in the UK. Two essential oil blends were used, either a combination of bergamot Citrus aurantium var. bergamia (Risso) and sandalwood Santalum austrocaladonicum, or frankincense Boswellia carterii (Birdw.), mandarin Citrus reticulata (Blanco), and lavender L. angustifolia. At least a one point improvement on the Likert Scale Measuring Sleep Quality was shown by 64% of patients, and 94% of participants who used the aromasticks said they would continue to do so. (5)
College students with self-reported sleep issues saw more improved sleep with nightly lavender L. angustifolia essential inhalation for five nights and sleep hygiene practices than the students who used sleep hygiene practices alone. The effects continued to be seen at the two-week follow up interview. (3)
Lowering Nausea and Vomiting
Several studies have been published showing good results for reducing nausea and vomiting with essential oil inhalation.
Inhalation of ginger Zingiber officinale (Roscoe) essential oil was shown to lower nausea and vomiting in adult post-operative patients. (7) However, when a blend of ginger Z. officinale, lavender L. angustifolia, peppermint Mentha xpiperita (L.), and spearmint Mentha spicata (L.) essential oil was used via inhalation to relieve nausea and vomiting in post-operative children, there was no statistical difference between aromatherapy and the saline placebo group. (6)
In a study assessing the effectiveness of ginger Z. officinale essential oil to relieve chemotherapy induced nausea and vomiting in breast cancer patients, researchers found nausea was relieved in the acute phase, but not for the duration of the five-day treatment. Also, the aromatherapy group reported better global health status and improvement in appetite loss. (8)
Lemon Citrus limon (Risso) essential oil was shown to lower nausea and vomiting of pregnant women over a four-day treatment period. The women in the aromatherapy group were encouraged to inhale the provided lemon C. limon essential oil at the first signs of nausea. (9)
Situational Stress and Anxiety
One of the primary focuses in research on essential oil inhalation has been around situational stress and anxiety.
Test Anxiety in Students
An Iranian study showed inhaling tuberose Polianthes tuberosa (L.) essential oil on a handkerchief for 15 minutes lowered anxiety in seventh-grade students while taking an exam, compared to the control group who inhaled saline solution. (10)
Pre-Operative and Post-Operative Patients
Several studies have shown aromatherapy inhalation lowers anxiety in patients about to undergo, or recovering from, different types of surgery. However, the results of these studies do show mixed results, which underlines the need for more research to better understand which factors affect aromatherapy outcomes.
Chest tube removal after cardiac surgery is a painful procedure which also causes anxiety. Lavender L. angustifolia essential oil inhalation, as well as a combination of lavender L. angustifolia essential oil inhalation and cold application, lowered pain and anxiety levels during the procedure and 15 minutes afterwards. (12) Inhalation of 2 drops of lavender L. angustifolia essential oil for 20 minutes lowered anxiety and cortisol levels in open heart surgery candidates. (11)
However, another study had coronary bypass patients inhale a 2% lavender L. angustifolia solution for three days post-surgery. Anxiety was lowered in the aromatherapy group, but there was no statistical difference between the aromatherapy and control groups. (14)
Inhalation of bitter orange Citrus aurantium (L.) essential oil prior to a bone marrow aspiration procedure for patients with chronic myeloid leukemia lowered anxiety, blood pressure, and cardiac and respiratory frequency. The effects in the aromatherapy group were more effective than the diazepam and control groups. (13)
However, a placebo-controlled, double-blind study did not find any statistical differences in the pain levels of children and adolescents undergoing stem cell infusion after bergamot C. aurantium var. bergamia essential oil inhalation. Also, nausea and anxiety levels were greater in the aromatherapy group one hour post procedure. The researchers felt perhaps a follow-up study would examine cutaneous aromatherapy applications and compare results. (17)
Lavender L. angustifolia and clary sage Salvia sclarea (L.) essential oils were both examined for lowering anxiety in female patients with urinary incontinence about to undergo a urodynamic exam. Interestingly, while both inhalation with clary sage S. sclarea or lavender L. angustifolia essential oil lowered respiratory rate, lavender essential oil tended to increase blood pressure in the situation, while clary sage S. sclarea lowered it. Based on these results, the researchers felt clary sage S. sclarea was more effective at lowering anxiety during the exam than lavender L. angustifolia. (16)
Night-shift Medical Staff
The anxiety level of nurses was shown to be lowered, over several days, by wearing a vial of 3% lavender L. angustifolia essential oil on the right chest of their uniforms during their shift. (15) Another study showed a 30-minute rest with lavender essential oil inhalation at the end of their shift improved the effects seen on endothelial function of night shift medical staff. (18)
Pregnancy, Labor and Delivery, and Post-Partum
The use of aromatherapy to support mothers during pregnancy, labor and deliver, and post-partum has been an important and increasing topic of discussion. Research focusing on establishing safe and effective best-practices guidelines is important. Several studies have focused on the effects of aromatherapy inhalations.
A pilot study evaluated the effects of aromatherapy inhalation and aromatherapy M hand technique on post-partum depression with a combination of rose Rosa damascena (Mill.) and lavender L. angustifolia essential oils in a 2% dilution. Participants received 15-minute aromatherapy sessions twice a week for four consecutive weeks. While there was a difference between the aromatherapy and control groups at the beginning of the study, at the mid-point and end of the study, the aromatherapy groups had significant improvements over the control group on the Edinburgh Postnatal Depression Scale (EPDS) and Generalized Anxiety Disorder Scale (GAD-7). (19)
Another study also evaluated aromatherapy support for post-partum depression using inhalations with 3 drops lavender L. angustifolia essential oil every eight hours for three weeks beginning right after delivery. Participants received routine care, and were followed-up with by telephone using the 21-item Depression, Anxiety, and Stress Scale and the Edinburgh Stress, Anxiety, and Depression Scale. At the two-week, one-month, and three-month check in points, all aromatherapy participants showed lowered mean stress, anxiety, and depression scores as compared to the control group. (20)
Anxiety During Labor
Nulliparous women (first-time mothers) also showed reduced anxiety and blood pressure during labor with the inhalation of geranium Pelargonium graveolens (L’Hér.) essential oil, compared to the control group. While this study had 100 total participants, the researchers did not specify how much geranium P. graveolens essential oil was used, or how the inhalation was performed. (21)
Pain Management after Cesarean Delivery
Lastly, the effects of lavender L. angustifolia essential oil inhalations were evaluated for the ability to lower pain after cesarean delivery. Patients were given approximately 3 drops of lavender L. angustifolia essential oil in a 10% dilution to inhale at the start of postoperative pain, and then four, eight, and 12 hours later. Patients receiving aromatherapy inhalations showed lower pain levels, more satisfaction with analgesia, and reduced heart rate. (22)
Premenstrual and Menopausal Emotional Support
A study performed in Japan explored the effects of yuzu Citrus junos (Siebold ex Tanaka) essential oil inhalation on the mood states and autonomic nervous system of women in the follicular and late-luteal phases of their menstrual cycles. It was noted that a 10-minute inhalation of yuzu C. junos essential oil decreased heart rate and increased the high frequency power of heart rate variability (HRV), regardless of menstrual phase, indicating parasympathetic nervous system activity. This effect was seen even 25 minutes after the inhalation. Also, decreases in total mood disturbance, anxiety, and fatigue were noted up to 35 minutes after inhalation, regardless of menstrual phase. (24)
The effects of lavender L. angustifolia essential oil inhalation on 22 women who had mild to moderate premenstrual symptoms was assessed in another study. The results show again that a 10-minute essential oil inhalation increased the high frequency power of HRV, indicating parasympathetic nervous system activity. Also, decreased scores for depression, dejection, and confusion were seen. (23)
A Korean study examined the effects of clary sage S. sclarea essential oil on 22 menopausal women who were evaluated to be in a normal or depression tendency group. Their findings showed a decrease in cortisol levels and an increase in the neurotransmitter 5-hydroxytryptamine (5-HT), also known as serotonin. These responses were seen in both the normal and the depression tendency groups. However, the cortisol decrease was more significant in the depression tendency groups. The researchers felt these results indicated an antidepressant action from clary sage essential oil inhalation. (25)
A randomized, double-blind study gave menopausal women five-minute inhalations of 0.1% and 0.5% neroli Citrus aurantium (L.) var. amara essential oil twice daily for five days. The results demonstrated relief in menopausal symptoms, increase in sexual desire, decrease in serum cortisol, and decrease in blood pressure. (26)
One study, with 54 participants, evaluated the effects of aromatherapy on symptoms, quality of life, sleep quality, and fatigue in adults with perennial allergic rhinitis. The aromatherapy group received inhalations using a combination of sandalwood Santalum album (L.), geranium P. graveolens, and ravensara Cryptocarya agathophylla (van der Werff) essential oils, while the control group received inhalations with sweet almond Prunus dulcis var. amara oil. Both groups performed five-minute inhalations, twice daily, for seven days. The aromatherapy group showed improvements in their Total Nasal Symptom Score, particularly nasal obstruction, and improvements in their Rhinitis-Specific Quality of Life Score, as well as reduced fatigue. (27)
Protective Effects During Radioactive Iodine Treatment
One every interesting study evaluated the protective effects of aromatherapy inhalations during radioactive iodine treatments (RAI). During radioactive iodine treatments for thyroid cancer, damage to salivary gland function can also occur. This study divided 71 patients with differentiated thyroid cancer into aromatherapy and controls groups during their RAI treatments. The aromatherapy group inhaled a combination of lemon C. limon and ginger Z. officinale essential oil (ratio of 2:1) for 10 minutes during the admission process for their treatment. The control group inhaled distilled water. The results showed an over trend for lower accumulation of radioactive iodine in the parotid and submandibular gland salivary glands, and stimulation of faster salivary secretion in the parotid salivary glands after the treatment to help washout the accumulated radioactive iodine. (28)
Autonomic Nervous System Activity
While the research above was focused on physical, mental, and emotional effects in specific situations, other research has been focused on understanding the systemic effects of aromatherapy on healthy individuals when delivered through essential oil inhalations. These effects have been measured primarily through autonomic nervous system activity.
A random crossover study evaluated the effects of 15-minute inhalations of bergamot C. aurantium var. bergamia essential oil followed by 10 minutes of rest. Results showed lowered salivary cortisol levels and an increase in high frequency HRV, both indicating parasympathetic nervous system activity. Also, scores improved for negative emotions and fatigue in the aromatherapy group. (29)
A study examining the essential oils of two Taiwanese conifer species, meniki Chamecyparis formosensis and hinoki Chamecyparis obtusa, found the effects of five-minute inhalations differed between the two species. Meniki C. formosensis essential oil showed evidence of increasing parasympathetic nervous system activity, with decreases in systolic blood pressure and heart rate, and an increase in diastolic blood pressure. Hinoki C. obtusa essential oil showed evidence of increasing sympathetic nervous system activity with increased systolic blood pressure and heart rate. Both essential oils promoted a pleasant mood. (30)
Rosemary Rosmarinus officinalis (L.) essential oil was shown to have stimulatory effects and increase sympathetic nervous system activity on healthy adult volunteers after a 10% rosemary essential oil solution was inhaled for 20 minutes through a respiratory mask. This study measured increases in blood pressure, heart rate, and respiratory rate, as well as decreases in alpha brain waves and an increase in beta brain waves. Participants reported feeling more active and “fresher” after the rosemary R. officinalis essential oil inhalation. These results supported rosemary essential oil’s traditional use as a stimulant. (31)
In reviewing these studies, essential oil inhalations have been shown to have measurable effects in a variety of situations, from the classroom to the hospital room to everyday life. Many types of people utilized aromatherapy inhalation to achieve stress and anxiety reduction, better sleep quality, pain relief, and mood improvement. However, the results are not always consistent, and this points to the need for more research investigating which factors can impact the outcome of aromatherapy in general, including essential oil inhalations.
There are several factors that could account for inconsistencies in the effects of essential oil inhalations, and these factors should be considered when evaluating and designing research on this topic, including: the method of inhalation; the duration of each inhalation session; the frequency of inhalation sessions; the amount of essential oil used; verifying essential oil composition; and choosing an essential oil or essential oil combination appropriate for the individual, situation, and desired effects. Throughout the research on essential oil inhalation, there are inconsistencies in these categories, making it difficult to assess their impact on the results.
Another factor which is not discussed as much in these research studies is the effects of aroma perception and expectations (32) by the participants. A strong like or dislike, or an expectation of an aroma can also impact the effects of an essential oil inhalation, particularly on mood states.
Nonetheless, the aromatherapist can still benefit from reviewing the current research, and use it when assessing their options for administering aromatherapy.
Improving Quality of Sleep
- Kim W., Hur MH. (2016). Inhalation Effects of Aroma Essential Oil on Quality of Sleep for Shift Nurses after Night Work. J Korean Acad Nurs. 46(6):769-779. doi: 10.4040/jkan.2016.46.6.769. https://www.ncbi.nlm.nih.gov/pubmed/28077825
- Karadag E, Samancioglu S, Ozden D, Bakir E. (2017) Effects of aromatherapy on sleep quality and anxiety of patients. Nurs Crit Care. 22(2):105-112. doi: 10.1111/nicc.12198. https://www.ncbi.nlm.nih.gov/pubmed/26211735
- Lillehei AS, Halcón LL, Savik K, Reis R. (2015). Effect of Inhaled Lavender and Sleep Hygiene on Self-Reported Sleep Issues: A Randomized Controlled Trial. J Altern Complement Med. 21(7):430-8. doi: 10.1089/acm.2014.0327. https://www.ncbi.nlm.nih.gov/pubmed/26133206
- Lytle J, Mwatha C, Davis KK. (2014) Effect of lavender aromatherapy on vital signs and perceived quality of sleep in the intermediate care unit: a pilot study. Am J Crit Care. 23(1):24-9. doi: 10.4037/ajcc2014958 https://www.ncbi.nlm.nih.gov/pubmed/24382614
- Dyer J, Cleary L, McNeill S, Ragsdale-Lowe M, Osland C. (2016) The use of aromasticks to help with sleep problems: A patient experience survey. Complement Ther Clin Pract. 22:51-8. doi: 10.1016/j.ctcp.2015.12.006. https://www.ncbi.nlm.nih.gov/pubmed/26850806
Lowering Nausea and Vomiting
- Kiberd MB, Clarke SK, Chorney J. d’Eon B, Wright S. (2016) Aromatherapy for the treatment of PONV in children: a pilot RCT. BMC Complement Altern Med. 16(1):450. https://www.ncbi.nlm.nih.gov/pubmed/27829428
- Lee YR, Shin HS. (2016) Effectiveness of Ginger Essential Oil on Postoperative Nausea and Vomiting in Abdominal Surgery Patients. J Altern Complement Med. Nov 14. Epub ahead of print https://www.ncbi.nlm.nih.gov/pubmed/27841938
- Lua PL, Salihah N, Mazlan N. (2015) Effects of inhaled ginger aromatherapy on chemotherapy-induced nausea and vomiting and health-related quality of life in women with breast cancer. Complement Ther Med. 23(3):396-404. doi: 10.1016/j.ctim.2015.03.009. https://www.ncbi.nlm.nih.gov/pubmed/26051575
- Yavari Kia P, Safajou F, Shahnazi M, Nazemiyeh H. (2014) The effect of lemon inhalation aromatherapy on nausea and vomiting of pregnancy: a double-blinded, randomized, controlled clinical trial. Iran Red Crescent Med J. 16(3):e14360. doi: 10.5812/ircmj.14360. https://www.ncbi.nlm.nih.gov/pubmed/24829772
Situational Stress and Anxiety
- Ghorat F, Shahrestani S, Tagabadi Z, Bazghandi M. (2016) The Effect of Inhalation of Essential Oils of Polianthes Tuberosa on Test Anxiety in Students: A Clinical Trial. Iran J Med Sci. 41(3):S13. https://www.ncbi.nlm.nih.gov/pubmed/27840479
- Hosseini S, Heydari A, Vakili M, Moghadam S, Tazyky S. (2016) Effect of lavender essence inhalation on the level of anxiety and blood cortisol in candidates for open-heart surgery. Iran J Nurs Midwifery Res. 21(4):397-401. doi: 10.4103/1735-9066.185582. https://www.ncbi.nlm.nih.gov/pubmed/27563324
- Hasanzadeh F, Kashouk NM, Amini S, Asili J, Emami SA, Vashani HB, Sahebkar A. (2016) The effect of cold application and lavender oil inhalation in cardiac surgery patients undergoing chest tube removal. EXCLI J. 22(15):64-74. doi: 10.17179/excli2015-748. https://www.ncbi.nlm.nih.gov/pubmed/27047319
- Pimenta FC, Alves MF, Pimenta MB, Melo SA, de Almeida AA, Leite J, et.al. (2016) Anxiolytic Effect of Citrus aurantium L. on Patients with Chronic Myeloid Leukemia. Phytother Res. 30(4):613-7. doi: 10.1002/ptr.5566. https://www.ncbi.nlm.nih.gov/pubmed/26787366
- Seifi Z, Beikmoradi A, Oshvandi K, Poorolajal J, Araghchian M, Safiaryan R. (2014) The effect of lavender essential oil on anxiety level in patients undergoing coronary artery bypass graft surgery: A double-blinded randomized clinical trial. Iran J Nurs Midwifery Res. 19(6):574-80. https://www.ncbi.nlm.nih.gov/pubmed/2555825315. Chen MC, Fang SH, Fang L. (2015) The effects of aromatherapy in relieving symptoms related to job stress among nurses. Int J Nurs Pract. 21(1):87-93. doi: 10.1111/ijn.12229. https://www.ncbi.nlm.nih.gov/pubmed/24238073
- Seol GH, Lee YH, Kang P, You JH, Park M, Min SS. (2013) Randomized controlled trial for Salvia sclarea or Lavandula angustifolia: differential effects on blood pressure in female patients with urinary incontinence undergoing urodynamic examination. J Altern Complement Med. 19(7):664-70. doi: 10.1089/acm.2012.0148. https://www.ncbi.nlm.nih.gov/pubmed/23360656
- Ndao DH, Ladas EJ, Cheng B, Sands SA, Snyder KT, Garvin JH Jr, et al. (2012) Inhalation aromatherapy in children and adolescents undergoing stem cell infusion: results of a placebo-controlled double-blind trial. Psychooncology. 21(3):247-54. doi: 10.1002/pon. https://www.ncbi.nlm.nih.gov/pubmed/2238326618. Shimada K, Fukuda S, Maeda K, Kawasaki T, Kono Y, Jissho S, et al. (2011) Aromatherapy alleviates endothelial dysfunction of medical staff after night-shift work: preliminary observations. Hypertens Res. 34(2):264-7. doi: 10.1038/hr.2010.228. https://www.ncbi.nlm.nih.gov/pubmed/21107332
Pregnancy, Labor and Delivery, and Post-Partum
- Conrad P, Adams C. (2012) The effects of clinical aromatherapy for anxiety and depression in the high risk postpartum woman – a pilot study. Complement Ther Clin Pract. 18(3):164-8. doi: 10.1016/j.ctcp.2012.05.002. https://www.ncbi.nlm.nih.gov/pubmed/2278979220. Kianpour M, Mansouri A, Mehrabi T, Asghari G. (2016) Effect of lavender scent inhalation on prevention of stress, anxiety and depression in the postpartum period. Iran J Nurs Midwifery Res. 21(2):197-201. doi: 10.4103/1735-9066.178248. https://www.ncbi.nlm.nih.gov/pubmed/27095995
- Rashidi Fakari F, Tabatabaeichehr M, Kamali H, Rashidi Fakari F, Naseri M. (2015) Effect of Inhalation of Aroma of Geranium Essence on Anxiety and Physiological Parameters during First Stage of Labor in Nulliparous Women: a Randomized Clinical Trial. J Caring Sci. 4(2):135-41. doi: 10.15171/jcs.2015.014. https://www.ncbi.nlm.nih.gov/pubmed/26161367
- Olapour A, Behaeen K, Akhondzadeh R, Soltani F, Al Sadat Razavi F, Bekhradi R. (2013) The Effect of Inhalation of Aromatherapy Blend containing Lavender Essential Oil on Cesarean Postoperative Pain. Anesth Pain Med. 3(1):203-7. doi: 10.5812/aapm.9570. https://www.ncbi.nlm.nih.gov/pubmed/24223363
Premenstrual and Menopausal Emotional Support
- Matsumoto T, Asakura H, Hayashi T. (2013) Does lavender aromatherapy alleviate premenstrual emotional symptoms?: a randomized crossover trial. Biopsychosoc Med. 7(12). doi: 10.1186/1751-0759-7-12. https://www.ncbi.nlm.nih.gov/pubmed/23724853
- Matsumoto T, Kimura T, Hayashi T. (2016) Aromatic effects of a Japanese citrus fruit-yuzu (Citrus junos Sieb. ex Tanaka)-on psychoemotional states and autonomic nervous system activity during the menstrual cycle: a single-blind randomized controlled crossover study. Biopsychosoc Med. 10(11). doi: 10.1186/s13030-016-0063-7. https://www.ncbi.nlm.nih.gov/pubmed/27103942
- Lee KB, Cho E, Kang YS. (2014) Changes in 5-hydroxytryptamine and cortisol plasma levels in menopausal women after inhalation of clary sage oil. Phytother Res. 28(11):1599-605. doi: 10.1002/ptr.5163 https://www.ncbi.nlm.nih.gov/pubmed/24802524
- Choi SY, Kang P, Lee HS, Seol GH. (2014) Effects of Inhalation of Essential Oil of Citrus aurantium L. var. amara on Menopausal Symptoms, Stress, and Estrogen in Postmenopausal Women: A Randomized Controlled Trial. Evid Based Complement Alternat Med. 2014:796518. doi: 10.1155/2014/796518.https://www.ncbi.nlm.nih.gov/pubmed/25024731
- Choi SY, Park K. (2016) Effect of Inhalation of Aromatherapy Oil on Patients with Perennial Allergic Rhinitis: A Randomized Controlled Trial. Evid Based Complement Alternat Med. 2016:7896081. doi: 10.1155/2016/7896081. https://www.ncbi.nlm.nih.gov/pubmed/27034695
Protective Effects During Radioactive Iodine Treatment
- Nakayama M, Okizaki A, Takahashi K. (2016) A Randomized Controlled Trial for the Effectiveness of Aromatherapy in Decreasing Salivary Gland Damage following Radioactive Iodine Therapy for Differentiated Thyroid Cancer. Biomed Res Int. 2016:9509810. doi: 10.1155/2016/9509810. https://www.ncbi.nlm.nih.gov/pubmed/28042578
Autonomic Nervous System Activity
- Watanabe E, Kuchta K, Kimura M, Rauwald HW, 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. Forsch Komplementmed. 22(1):43-9. doi: 10.1159/000380989. https://www.ncbi.nlm.nih.gov/pubmed/25824404
- Chen CJ, Kumar KJ, Chen YT, Tsao NW, Chien SC, Chang ST, et al. (2015) Effect of Hinoki and Meniki Essential Oils on Human Autonomic Nervous System Activity and Mood States. Nat Prod Commun. 10(7):1305-8.https://www.ncbi.nlm.nih.gov/pubmed/26411036
- Sayorwan W, Ruangrungsi N, Piriyapunyporn T, Hongratanaworakit T, Kotchabhakdi N, Siripornpanich V. (2013) Effects of inhaled rosemary oil on subjective feelings and activities of the nervous system. Sci Pharm. 81(2):531-42. doi: 10.3797/scipharm.https://www.ncbi.nlm.nih.gov/pubmed/23833718
Factors which could affect outcome of inhalation administration
- Köteles F, Babulka P. (2014) Role of expectations and pleasantness of essential oils in their acute effects. Acta Physiol Hung. 101(3):329-40. doi: 10.1556/APhysiol.101.2014.3.8.https://www.ncbi.nlm.nih.gov/pubmed/25183507