What’s the connection between our sense of smell, our emotions and memories?

And how do essential oils fit in the picture?

“Yum! It smells like grandma’s pie!”. Or cake. Or food. Ever heard a similar phrase?

Even better, did you ever smell something and got instantly teleported back in time, to one of your favorite memories?

What role does the sense of smell play in all of this? Well, quite a big one! Out of all our senses, it has maybe the most direct and least filtered impact on our state of being. That’s why, for example, when you feel a disgusting smell, you sometimes feel a reaction of repulsion even in your stomach!

But how exactly does this work? Let’s explore a bit!

The exact mechanics of how the sense of smell actually works are still being explored. There are various theories, trying to describe the complex process.

The most commonly used one is based on a lock and key mechanism – there are specific receptors in our nose that can identify specific molecules that “fit” just like a key in a lock. This theory does have some limitations, as it can not explain why similarly shaped molecules smell very differently (for example ethanol smells like vodka, whereas ethanethiol, having a similarly shaped molecule, smells like rotten eggs).

A newer theory, called the Vibration theory, starts from the assumption that the vibrational properties of molecules allow us to distinguish smells.

Regardless of how our noses actually detect smells, what happens next is agreed upon by everybody. Aromatic molecules travel up the nostrils, reaching the olfactory epithelium. The olfactory receptors are triggered, and the olfactory bulb then transmits impulses to other parts of the brain, like the gustatory center (the sensation of taste is perceived here – so this explains why food tastes more bland when we have a congested nose!) and the limbic system.

The limbic system is a relatively small part of our brain, but it plays some of the most basic and life sustaining roles! There are several parts of the limbic system, amongst which the hypothalamus, the hippocampus, the amygdala and other related areas. It is primarily responsible for our emotional life, and has a lot to do with with the formation of memories. It also has a major impact on what we call homeostasis – keeping things balanced in our bodies. Much like a thermostat keeping the temperature in a room in a certain range. The hypothalamus regulates hunger, thirst, pain response, pleasure levels, sexual satisfaction, anger, aggressiveness etc. It also regulates things like your pulse, blood pressure, breathing, arousal. The fight or flight response? Also controlled by the limbic system.

Ok, ok… I get it, the limbic system is an important part of the brain. But still, how is this related to the sense of smell and essential oils?

Well, our bodies transmit sensory information to the thalamus – the switchboard of the brain. With one exception – you guessed it, smells! The sense of smell has a direct, unfiltered impact on our limbic systems, triggering immediate responses. And since the limbic system also controls so many other processes in our bodies, inhaling essential oils can have a big impact on our overall state. Inhaling essential oils can be used to combat stress and emotional trauma, and even to stimulate the production of hormones from the hypothalamus.

What does the research say?

There’s more and more research papers looking at how aromatic compounds, essential oils and aromatherapy can benefit us. I am listing some of the findings below:

1. In a large clinical study, Alan Hirsch used fragrances, including peppermint, to trigger weight loss in a group of 3193 overweight volunteers. The study concluded that “it may be possible for individuals with good olfaction, y inhaling certain aromas, to induce and sustain loss of weight over a 6-month period” (Hirsch, A. R., and R. Gomez. “Weight reduction through inhalation of odorants.” Journal of Neurological and Orthopaedic Medicine and Surgery 16 (1995): 28-28.)
2. “Over the past few years a number of clinical trials have compared aromatherapy, principally using either lavender (Lavandula angustifolia or Lavandula officinalis) or lemon balm (Melissa officinalis), with inactive treatment. All of these studies demonstrated a significant impact on behavioural problems in patients with dementia, with negligible side-effects.” (Holmes, Clive, and Clive Ballard. “Aromatherapy in dementia.” Advances in psychiatric treatment 10.4 (2004): 296-300.)
3. Fragrance compounds and essential oils proved to have sedative effects on mice, including on ones that were artificially induced into overagitation using caffeine! (Buchbauer, Gerhard, et al. “Fragrance compounds and essential oils with sedative effects upon inhalation.” Journal of pharmaceutical sciences 82.6 (1993): 660-664.)
4. Anti stress action of essential oils of Lavender, Rose, Lemon were examined. Furthermore, a regulatory mechanism for the lemon oil was investigated. Conclusion: “These results suggest that lemon oil possesses anxiolytic, antidepressant-like effects via the suppression of DA activity related to enhanced 5-HTnergic neurons.” (Komiya, Migiwa, Takashi Takeuchi, and Etsumori Harada. “Lemon oil vapor causes an anti-stress effect via modulating the 5-HT and DA activities in mice.” Behavioural brain research 172.2 (2006): 240-249.)
5. The effects of Lavender essential oil were also compared with the effects of  chlordiazepoxide (CDP), as a reference anxiolytic (a medication that inhibits anxiety). The “experiments suggest that lavender oil does have anxiolytic effects in the open field, but that a sedative effect can also occur at the highest doses.” (Shaw, David, et al. “Anxiolytic effects of lavender oil inhalation on open-field behaviour in rats.” Phytomedicine 14.9 (2007): 613-620.)
6. “Studies have shown that essential oils have an effect on brainwaves and can also alter behaviour. It is possible that most of the effect of the oils is probably transmitted through the brain via the olfactory system. Used professionally and safely, aromatherapy can be of great benefit as an adjunct to conventional medicine or used simply as an alternative.” (Lis-Balchin, Maria. “Essential oils and’aromatherapy’: their modern role in healing.” Journal of the royal society of health117.5 (1997): 324-329.)
7. “Odors are capable of altering emotional states and may indicate that the use of odors is helpful in reducing anxiety in dental patients.” (Lehrner, Johann, et al. “Ambient odors of orange and lavender reduce anxiety and improve mood in a dental office.” Physiology & Behavior 86.1-2 (2005): 92-95.)
8. Memories and smell become tied together! (Kesner, Raymond P., Michael R. Hunsaker, and Warren Ziegler. “The role of the dorsal and ventral hippocampus in olfactory working memory.” Neurobiology of learning and memory 96.2 (2011): 361-366.)

And this is just the tip of the iceberg – there are countless other studies out there.

Bottom line? Essential oils are not simple perfumes – their complexity and value comes from the hundreds of different components acting synergistically, influencing also our limbic systems.