Aromatherapist Ellen Rowland shares a section from her book on what smell is and how it can affect our wellbeing.
Excerpt from Chapter 1: What is smell?
Scent and Sensitivity: Aromas and the nervous system
Our nervous system is very sensitive to scent. When we detect an aroma, the limbic system, a collection of structures in our brain that includes the thalamus, hypothalamus and amygdala, comes into play. This is the part of our brain which relates to mood and emotion. The amygdala in particular, the first port of call for odours reaching the brain, is concerned with interpreting the âemotional significance of events in the external world (33).
Smells have a direct impact on our nervous systems since inhaling them can trigger the release or inhibition of certain hormones into the bloodstream. These can activate or inhibit our parasympathetic (our ârest and digestâ mode) or sympathetic nervous systems (âfight/flight/freezeâ) by way of the hypothalamus, which controls our autonomic nervous system, of which the parasympathetic and sympathetic system are the main parts. This influence is due to the scent moleculesâ direct link to the amygdala and hypothalamus (34). Current science understands that aroma signals mostly bypass the thalamus (35), the part of our brain that deals with conscious recognition, and are transmitted straight to the hypothalamus, which has a major influence on the endocrine (hormonal) system. As such, aromas are not always consciously processed by the frontal cortex, where our usual cognition and interpretation occurs (36), and so the influence aromas have on our body and mind is thought not always to be consciously processed by our brain (18).
Clinical aromatherapy research in practice
Several research studies and systematic reviews have demonstrated the positive effects of different aromas on mood disorders like depression (52), noted improvements in cognitive function in mice, suggesting that aromatherapy could be an effective treatment for Alzheimerâs disease (53), and recorded reduced stress levels in teenagers within academic environments (54). Anxiety in dental waiting rooms has been abated by aromatherapy (55), menopausal anxiety and depression have been relieved,56 and it has been shown to âsignificantly decreaseâ (57) labour pain and anxiety. Midwives in the UK do, on occasion and with appropriate training and experience, offer aromatherapy through inhalation and massage to their pregnant patients â this is perhaps the most widely accepted form of aromatherapy within mainstream healthcare contexts like the NHS (National Health Service, UK), probably due to its efficacy (58) and relative safety (59).
Aromatherapy has also been shown to improve postpartum âdepression, fatigue, sleep quality, pain after caesarean delivery and post-episiotomy painâ (60) and reduce dysmenorrhea, too, so it is a useful and gentle tool for those who are pregnant or postpartum people to carry all the way through their pregnancy, birth and on into parenthood. In my aromatherapy clinic, for example, I offer a specialised workshop for parents-to-be, which includes a bespoke pregnancy massage tutorial, and a series of customised inhalation and massage oil blends for the three trimesters, as well as specific blends for use during labour. I also provide follow-up information and postpartum products, such as balms or oil blends, if the clients prefer. My clients and I have found this to be an enjoyable, holistic and gentle approach to ensuring that parents and their birth partners feel supported throughout their pregnancy. Treatment can normally be given alongside and in respect of ongoing treatment or appointments within mainstream healthcare.
Biochemistry and the brain: How scent influences mood
The ability of aromas to influence our nervous systems can cause us to feel anger, joy, or fear by altering our biochemistry, impacting both our physical states and mood (39). To understand how this works on a biochemical level, letâs explore the key hormones and brain structures associated with this influence.
Amygdala
This structure is part of the limbic system of our brain, and is responsible for mediating emotions such as fear, aggression and anxiety (40). It does this by sending signals of distress via the nervous system to our adrenal glands, which are located on the top of our kidneys. These glands secrete the hormone epinephrine (adrenaline) and cortisol (41) into our bloodstream (42) which results in stimulation of the sympathetic nervous system, otherwise known as the âfight or flightâ response. When we enter this state, our heart rate increases, sending more blood and oxygen around the body, and our breathing speeds up (43) This is a natural response to stressful situations and the bodyâs natural way of preparing us to encounter (or run away from) life-threatening situations. However, in conditions like Generalised Anxiety Disorder or chronic stress, this response can activate inappropriately (44) and cause health problems, both physical and psychological (45). Thankfully, scent can be used to âteachâ the nervous system that it is safe, causing inhibition of the sympathetic nervous system, and activation of the parasympathetic nervous system â our ârest and digestâ mode. Later, weâll explore how this works.
Hypothalamus
This brain structure is also part of the limbic system and is responsible for the release or inhibition of hormones. Hormones (including dopamine, the âfeel-goodâ or âpleasureâ hormone) (46,47) are released into the bloodstream and go on to stimulate the pituitary gland to produce more hormones (such as oxytocin, the âlove hormoneâ) (48) which influence our thyroid and adrenal glands, reproductive system and autonomic nervous system (49). Since the hypothalamus is the area âwhere the nervous system and endocrine [hormonal] system overlapâ (50), this cascade of hormones can have an impact on anything from our mood, to our sleep and metabolism (51).
In fact, we already have access to this invention: scent is the key to the revival of vivid memories. The brainâs limbic system, in addition to regulating mood and emotion, is also responsible for the creation of memory associations. More specifically, the hippocampus, which is the area of the brain that converts short-term memory to long-term memory (63). In a 2020 talk, âOlfaction in Science and Societyâ, sponsored by the Harvard Museum of Natural History, Dawn Goldworm, co-founder of an olfactive branding company, 12.29, explains:
ââŠsmell and emotion are stored as one memory
and childhood is usually the time of life in
which you create the basis for smells you will
like and hate for the rest of your life.â (64)
While not bottled, these scent-memories are contained subconsciously within the brainâs anterior olfactory nucleus (65), and are âuncorkedâ when triggered by a certain vocative scent. The smell of mown grass, lavender laundry water in a grandmotherâs garden, campfire woodsmoke on a cherished holiday, pine disinfectant on freshly-scrubbed bathroom floors, cedar moth repellent in an old wardrobe, seaweed drying in the sun, and toasting bread in a family home are all scent-memories that students on my aromatherapy and herbalism workshops and retreats have recalled when I have asked which aromas evoke memory responses for them. For some people, the same aroma will have a range of responses, and they can differ wildly! Just as no two lives are alike, it is seldom that two people will have the same associations with a
particular scent.
Memories of scent
âOur senses connect us intimately to the past, connect us in
ways that most of our cherished ideas never couldâ
Diane Ackerman, A Natural History of the Senses (61)
As well as their neurological and hormonal effects, aromas can influence our mood through memories and associations. Have you ever been walking down the street, and caught a scent on the breeze that immediately transported you back in time, or to a cherished place from your childhood? For me, the smell of eucalyptus has always transported me back to a park on the coast in Tasmania, Australia, where I lived for a year when I was eight years old. Not only is the scent strongly associated with a sense of place, but the colours, textures and sounds, even the breeze and temperature, come clearly into my mindâs eye. When I inhale the resinous, baked and distinctive aroma of the leaves as the sun gently warms them and releases their oils, I picture the park swings, the chipped bark underfoot, and the afternoon light on the wet rocks and dancing across the ocean. I can almost see the seabirds fishing, and feel the breeze and sunlight on my skin.
So why is scent such a powerful and seemingly magical conjurer when it comes to memory? Itâs all to do with the limbic system again. In her 1938 novel, Rebecca, Daphne du Maurierâs protagonist wishes:
“If only there could be an invention that
bottled up a memory, like scent. And
it never faded, and it never got stale.
And then, when one wanted it, the bottle
could be uncorked, and it would be like
living the moment all over again.”
Daphne du Maurier, Rebecca (62)
Whatâs more, the client is then able to take a blend of these aromatic oils with them when they leave the treatment space, by way of an inhaler, roll-on oil blend, or room spray, which with time and practice, will enable them to conjure up the new, positive association when they are struggling to sleep or experiencing high levels of stress, and will have a positive, relaxing effect on their nervous system, emotions and muscles (70). This is what is known as a âlearned odour responseâ (71) and can easily and effectively be employed in a number of different scenarios to elicit âmeasurable effects on cognitive performance, stress, and moodâ (72).
Making new memories
While most scent-memory associations may be crafted and cemented during childhood, as adults we do have the ability to influence, change and create new associations (66). As a practising aromatherapist, before beginning a treatment, I make sure to ask my clients whether there are any aromas they know they absolutely cannot bear so that I avoid triggering any negative scent-memory-emotion responses, and I try to use essential oils and extracts with which they have already formed positive associations. For example, if a client is working with a particular challenge, such as insomnia, we might work together through the course of our treatments to create new aroma-memory associations. Since our brains are plastic (67) (they can learn, adapt and change), and have the amazing ability to form new scent associations through âinduce[d] emotional olfactory learningâ,68 aromatherapists are uniquely placed to support their clients to create and build an association between the scent of German chamomile (Matricaria recutita) and lavender (Lavandula angustifolia), for example.
The relaxing, dimly-lit ambience and safe, therapeutic space that the treatment room provides will further enhance this association. Since odours âvividly trigger the evocation of emotional experiencesâ(69), over the course of regular consultations and treatments, we can build a trusting, therapeutic relationship and work together to strengthen and reinforce the message we are sending to the clientâs brain. The aromas of German chamomile and lavender in combination with a soothing massage treatment, a warm, calming space and a listening ear, is effectively telling their brain âIâm safeâ, âI can relaxâ, âI can feel calm and happyâ and âitâs time to sleepâ.
Olfactory fatigue
In her book, Fragrant: The Secret Life of Scent, Mandy Aftel mentions a phenomenon known as âolfactory fatigueâ whereby the overstimulation of our olfactory organ can distort and weaken our ability to perceive different aromas (73). Have you ever tried smelling samples of perfume, or flowers, only to find that after a while you can no longer detect the different notes and aromas? Or perhaps all the scents start to smell the same? This is olfactory fatigue. Contrary to popular belief, smelling coffee beans will not âreset your noseâ, and actually, Aftel argues, smelling something made out of wool might be a better alternative. Science and food author Harold McGee, in his book Nose Dive, states that lanolin, the waxy coating found on wool, âholdsâ onto aromas (74). Perhaps this is why wool works well as a sort of âolfactory reset buttonâ.
References
33. V S Ramachandran and Sandra Blakeslee, Phantoms in the Brain (New York: William Morrow & Co, 1998), quoted in Ingrid Martin, Aromatherapy for Massage Practitioners (Baltimore, MD: Lippincott Williams & Wilkins, 2007), 27.
34. Ingrid Martin, Aromatherapy for Massage Practitioners (Baltimore, MD: Lippincott Williams & Wilkins, 2007), 28.
35. Gordon M Shepherd, âPerception without a Thalamus,â Neuron 46, no. 2 (April 21, 2005): pp. 166-168, https://doi.org/10.1016/j.neuron.2005.03.012.
36. Jennifer Peace Rhind, Fragrance and Wellbeing: Plant Aromatics and Their Influence on the Psyche (London: Singing Dragon, 2014), 19.
37. âEnding Smell Disorders,â AbScent, accessed August 24, 2023, https://abscent.org/. Note that the AbScent charity ceased operations in February 2024.
38. Neisa Santos Pissurno et al., âAnosmia in the Course of Covid-19,â Medicine 99, no. 31 (2020), https://doi.org/10.1097/md.0000000000021280.
39. Ingrid Martin, Aromatherapy for Massage Practitioners (Baltimore, MD: Lippincott Williams & Wilkins, 2007), 27.
40. Goran Ć imiÄ et al., âUnderstanding Emotions: Origins and Roles of the Amygdala,â Biomolecules 11, no. 6 (2021): p. 823, https://doi.org/10.3390/biom11060823.
41. Robert M Sargis, âAn Overview of the Pituitary Gland – Endocrineweb,â An Overview of the Pituitary Gland (EndocrineWeb, June 8, 2009), https://www.endocrineweb.com/
endocrinology/overview-pituitary-gland.
42. âUnderstanding the Stress Response,â Harvard Health (Harvard Health Publishing, July 6, 2020), https://www.health.harvard.edu/staying- healthy/understanding-the-stress-response
43. Ibid.
44. Suma P Chand and Raman Marwaha, âAnxiety,â in StatPearls (Treasure Island, FL:
StatPearls Publishing, 2022), https://www.ncbi.nlm.nih.gov/books/NBK470361/.
45. Bruce S McEwen, âThe End of ‘Stress’ as We Know It,â The end of ‘stress’ as we know it, Society for Endocrinology (Society for Endocrinology, 2018), https://www.endocrinology.org/endocrinologist/130-winter18/features/the-end-of-stress-as-we-know-it/.
46. âDopamine: What It Is, Function & Symptoms,â Cleveland Clinic, March 23, 2022, https://
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47. Stephanie Watson, âDopamine: The Pathway to Pleasure,â Harvard Health (Harvard
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48. Stephanie Watson, âOxytocin: The Love Hormone,â Harvard Health (Harvard Health Publishing, July 20, 2021), https://www.health.harvard.edu/mind-and-mood/oxytocin-the-love-hormone.
49. Zainab Shahid, Edinen Asuka, and Gurdeep Singh, âPhysiology, Hypothalamus,â accessed February 20, 2023, https://www.ncbi.nlm.nih.gov/books/NBK535380/.
50. Ingrid Martin, Aromatherapy for Massage Practitioners (Baltimore, MD: Lippincott Williams & Wilkins, 2007), 28.
51. Asya Rolls, Jana Schaich Borg, and Luis de Lecea, âSleep and Metabolism: Role of Hypothalamic Neuronal Circuitry,â Best Practice & Research Clinical Endocrinology & Metabolism 24, no. 5 (October 2010): pp. 817-828, https://doi.org/10.1016/j.beem.2010.08.002.
52. Dalinda Isabel SĂĄnchez-Vidaña et al., âThe Effectiveness of Aromatherapy for Depressive Symptoms: A Systematic Review,â Evidence-Based Complementary and Alternative Medicine 2017 (January 4, 2017): pp. 1-21, https://doi.org/10.1155/2017/5869315.
53. Michiaki Okuda et al., âAromatherapy Improves Cognitive Dysfunction in Senescence- Accelerated Mouse Prone 8 by Reducing the Level of Amyloid Beta and Tau Phosphorylation,â PLOS ONE 15, no. 10 (2020), https://doi.org/10.1371/journal.pone.0240378.
54. Yuanguang Ma, âThe Influence of Ambient Aroma on Middle School Students’ Academic Emotions,â International Journal of Psychology 57, no. 3 (2022): pp. 387-392, https://doi.org/10.1002/ijop.12827.
55. J Lehrner et al., âAmbient Odor of Orange in a Dental Office Reduces Anxiety and Improves Mood in Female Patients,â Physiology & Behavior 71, no. 1-2 (October 2000): pp. 83-86, https:// doi.org/10.1016/s0031-9384(00)00308-5.
56. Kenji Yamada et al., âEffect of Inhalation of Chamomile Oil Vapour on Plasma ACTH Level in Ovariectomized-Rat under Restriction Stress.,â Biological and Pharmaceutical Bulletin 19, no. 9 (September 1996): pp. 1244-1246, https://doi.org/10.1248/bpb.19.1244.
57. Mahbubeh Tabatabaeichehr and Hamed Mortazavi, âThe Effectiveness of Aromatherapy in the Management of Labor Pain and Anxiety: A Systematic Review,â Ethiopian Journal of Health Sciences 30, no. 3 (May 2020), https://doi.org/10.4314/ejhs.v30i3.16.
58. Ibid.
59. Ingrid Martin, Aromatherapy for Massage Practitioners (Baltimore, MD: Lippincott Williams & Wilkins, 2007), 160.
60. Mahbubeh Tabatabaeichehr and Hamed Mortazavi, âThe Effectiveness of Aromatherapy in the Management of Labor Pain and Anxiety: A Systematic Review,â Ethiopian Journal of Health Sciences 30, no. 3 (May 2020), https://doi.org/10.4314/ejhs.v30i3.16.
61. Diane Ackerman, A Natural History of the Senses (Phoenix, 1996), xvi.
62. Daphne Du Maurier, Rebecca (Harmondsworth: Penguin Books Ltd, 1938), https://archive.org/details/in.ernet.dli.2015.461023.
63. âLimbic System: Structure and Function: Emotion (Video),â Khan Academy (Khan Academy, 2023), https://www.khanacademy.org/test-prep/mcat/processing-the-environment/
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64. Colleen Walsh, âHow Scent, Emotion, and Memory Are Intertwined – and Exploited,â Harvard Gazette (Harvard Gazette, February 27, 2020), https://news.harvard.edu/gazette/story/2020/02/how-scent-emotion-and-memory-are-intertwined-and-exploited/.
65. Afif J. Aqrabawi and Jun Chul Kim, âOlfactory Memory Representations Are Stored in the Anterior Olfactory Nucleus,â Nature Communications 11, no. 1 (June 2020), https://doi.org/10.1038/s41467-020-15032-2.
66. Ingrid Martin, Aromatherapy for Massage Practitioners (Baltimore, MD: Lippincott Williams & Wilkins, 2007), 29.
67. Bryan Kolb and Robbin Gibb, âBrain Plasticity and Behaviour in the Developing Brain,â ed. Margaret Clarke and Laura Ghali, Journal of the Canadian Academy of Child and Adolescent Psychiatry (Journal De L’AcadĂ©mie Canadienne De Psychiatrie De L’enfant Et De L’adolescent) 20, no. 4 (November 2011): pp. 265-276, https://doi.org/10.1016/b978-0-444-63327-9.00005-9.
68. A M Mouly and R Sullivan, â15 – Memory and Plasticity in the Olfactory System: From Infancy to Adulthood.,â in The Neurobiology of Olfaction, ed. A Menini (Boca Raton, FL:
CRC Press/Taylor & Francis, 2010).
69. Ibid.
70. Ingrid Martin, Aromatherapy for Massage Practitioners (Baltimore, MD: Lippincott
Williams & Wilkins, 2007), 29.
71. Ibid.
72. Sam Gochman, âScentimental Associations with Nature: Odor-Associative Learning and Biophilic Design,â Terrapin Bright Green (Terrapin Bright Green, May 9, 2016), https://www.terrapinbrightgreen.com/blog/2016/05/scentimental-associations-with-nature/.
73. Mandy Aftel, Fragrant: The Secret Life of Scent (New York, New York: Riverhead Books, 2014), 3.
74. Harold McGee, Nose Dive: A Field Guide to the World’s Smells (London, UK: John Murray, 2020), 86.
