10 Facts About Our Sense of Smell

Today is National Sense of Smell Day. Our sense of smell is more than just a way to know that dinner is ready. It plays a huge role as an early warning system, and for emotional well-being and triggering memories. Ironically, it is the least studied and understood sense that we have. What little we do know, is truly remarkable! When we understand more about how our sense of smell works, we appreciate it so much more! As an aromatherapist, I am constantly learning about this invisible sense; and how it differs from person to person and plays a huge role in our daily lives. Here are 10 facts to better understand your sense of smell.

10 Facts About Our Sense of Smell

1) Smell is the oldest, most powerful sense.

Smell is the most underutilized sense we have yet one of the most powerful. It is our most primal sense and was used throughout evolution to determine a threat in the environment. The sense of smell is one of the first to develop in utero. A baby's nose starts to form early in the 1st trimester. The baby’s nasal cavity is fully formed and the chemoreceptors for smelling are ready as early as 9 weeks gestation.  They are fully connected to the brain at 13 weeks gestation.  At birth, smell is the most advanced sense. Newborn orient themselves by smell more than any other sense and when placed on a mother's belly after birth, they will work their way up to the breast navigating by sense of smell alone. (1)

Our sense of smell stops us from drinking sour milk, alerts us to natural gas, and can even detect a fire 30 miles away. While other mammals, such as dogs and cats have a much keener sense of smell, the human sense is still extraordinary with the human genome being packed with over 950 odorant receptor genes. Not to mention it’s the only sense that taps directly into the part of the brain responsible for emotion and memory.

2) Smell is the only sense connected directly to the emotional part of the brain.

A smell can stop us in our tracks. It is a protective mechanism can also bring joy to our lives.  There is a reason why so many companies use aromas to help them sell products through scent marketing. Aromas influence our emotions and therefore our behaviors. Why this strong connection? This is due to the anatomy of our olfactory system and its connection to the limbic system within the brain.

We inhale an aroma; odorant molecules trigger electrical signals within our olfactory bulb.

Nerve axons extend to the pryimidal cortex and then to limbic system. 

Structures within limbic system are responsible for emotions, behaviors, motivation and forming long term memory.  More specifically the amygdala (fight or flight stress response) and hippocampus. Aromas have been shown to evoke emotion and autonomic state through pathways to the amygdala. (2)

How is this different than other senses?

When we touch, taste, hear or see something it first goes to the thalamus which processes it and sends it to the cerebral cortex for interpretation.  Our sense of smell goes straight to amygdala and hippocampus which could play a huge role in whey smells trigger emotions and vivid emotional memories. This could also be a reason why our sense of smell triggers more emotional vivid memories than any other sense.

“Our primitive olfactory cortex was the first fabric of our brain and from this neural tissue grew the amydala where emotions are processed...in other words our ability to experience and express emotion grew direct out of our brain's ability to process smells.” (3)
-Dr. Rachel Herz, Psychologist and Cognitive Neuroscientist

3) Our sense of smell is directly connected with our breath.

This likely doesn’t come as a surprise to you but our smell is also the only sense directly connected with our breath.  We breathe around 23,000 times a day. Our breathing tells us a lot about what is going on inside emotionally and most of this is subconsciously as often we tend to avoid or deny unpleasant emotions. We sigh when we are tired, sad or frustrated but also when we are relieved.  Sighs are involuntary and exist to reset our breathing patterns which also influence our limbic system.  When we are anxious, we take short shallow breaths...these can precipitate further anxious feelings.

When we take a minute and breathe in a pleasant aroma, we are not only getting those physiological benefits of those odorant molecules but also the benefits of breathing deep into our lower lungs which are rich in parasympathetic nerve receptors. Aromatherapy in particular has been shown to increase heart rate variability which improves vagal tone and provides calming effects via the Vagus nerve. (4, 5, 6,)

4) We can recognize and form memories from approximately 10,000 different odors.

How many different aromas odors can you recognize and form memories from? 10,000!!!

The Nobel Prize in Physiology or Medicine in 2004 was awarded jointly to Richard Axel and Linda Buck for their discoveries of odorant receptors and the organization of the olfactory system. Axel and Buck discovered a large gene family of 1,000 different genes (3 percent of our genes) that are used to code for different odorant receptors on the membrane of olfactory receptor cells. They showed that every single olfactory receptor cell expresses only one odorant receptor gene, and each receptor cell reacts to several related odorant molecules. Since most odors are composed of multiple molecules, each molecule activates several odorant recptors which crease an “odorant pattern or map.” This is the basis for our ability to recognize and form memories of approximately 10,000 different odors. (7) Fascinating isn’t it?

5) The sense of smell evokes more emotionally vivid memories than any other sense

Have you ever passed by a bakery and inhaled the aroma of warm bread or cookies and immediately are brought back to a childhood memory of your grandma? Or smelled freshly mowed grass and thought of your dad? Does the smell of playdoh bring you right back to 1st grade again?

“Smell is the potent wizard that transports you across thousands of miles and all the years you have lived. The odors of fruits waft me to to my southern home, to my childhood frolics in the peach orchard. Other odors, instantaneous and fleeting, cause my heart to dilate joyously or contract with remembered grief. Even as I think of smells, my nose is full of scents that start to awake sweet memories of summers gone and ripening fields far away.”

-Helen Keller

Have you heard of the Proust Phenomenon? The Proust phenomenon refers to the appearance of seemingly forgotten, emotionally vivid, autobiographical memories evoked by scent. Marcel Proust was a French novelist from the 1920’s who was interested in understanding why some sense could trigger certain memories that we once lost. His research led to the “Proust Phenomenon” which refers to the appearance of seemingly forgotten, emotionally vivid, autobiographical memories evoked by scent.

The hippocampus within the limbic system is responsible for forming long term memories. Due to this direct connection of the olfactory and limbic system, scent evokes more emotional and evocative recollections than memories triggered by any other cue. (8)

6) We can utilize odor conditioning to reduce stress and calm the mind

Due to the anatomy of the olfactory system and its direct connection with the limbic system, your brain will begin to form memory scent associations of certain scents and relaxation. This is also known as odor conditioning. Scents that soothed children can continue to alleviate stress and anxiety for the entirety of adulthood. Scents that triggered anger and sadness can continue to result in negative emotions for years to come.

Studies have found that odors can transform emotions through association and then act as proxies for emotions, influencing how we feel later on. (9)

-Dr. Rachel Herz, a well-known Cognitive Neuroscientist.

Due to the complex chemical constituents, essential oils can play a role in transforming unpleasant emotions, inducing relaxation and potentially reducing the damaging effects of stress on the mind and body. Knowing this, we can utilize odor conditioning with aromatherapy. Start using those essential oils you find most pleasant with stress relieving activities such as a bath, during yoga, meditation, in massage or in a diffuser when unwinding after a long day.

7) We have olfactory receptors not just in our nose.

Researchers have found olfactory receptors outside of the nasal cavity in several other locations within the body that are functional. (10) These olfactory receptors play a role in kidney and lung physiology, hair growth, wound healing, metabolic control and function. They have even found there is abundant MRNA of olfactory receptors located within the testes and scientists believe this plays a role in how sperm finds the egg. In a lab in Germany led by Dr. Hanns Hatt, who is an olfactory physiologist, found that a component of essential oils activates olfactory receptors found on cancerous prostrate cells. (11)

8) Olfactory receptor cells regenerate every 30-60 days.

While nerve cells are typically very difficult to regenerate, our olfactory receptor cells are unique as they are being regenerated every 30 days to replace neurons damaged by exposure to our environment. (12) This may play a role in influencing our olfactory perceptions and why we are drawn to different scents in different seasons.

9) During pregnancy there is a huge burst of new olfactory neurons which heightens the sense of smell.

Early during pregnancy there is a huge burst in the production of new olfactory neurons. They are fully functional around the time of birth, and the scientist who discovered this speculated that these new olfactory neurons are tagged for the task of imprinting forever on the smell of your offspring. This is a critical event for mothers of all mammals. The new olfactory neurons which show up in early pregnancy may have something to do with the famed nausea, food aversions and olfactory sensitivities. (13)

10) Women have a stronger sense of smell than men.

A study done in 2014 showed that the number of cells in olfactory regions specifically neurons differ greatly between men and women. It was found that although the olfactory bulbs weighed basically the same, there was a 43% increase in the total number of cells in the female bulb. (Females had 16.2 million cells whereas men had 9.2 million cells.) As far as neurons, females had reached 6.9 million whereas men had no more than 3.5 million neurons, a difference of 49.3%. (14) These differences may have functional impact but it’s difficult to determine without knowing the special circuits cells make. This may play a role in why women tend to have a stronger sense of smell than men.

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Isn’t our sense of smell so incredible? Knowing about all of its benefits, I want to encourage you to use it more! Become more consciously aware of scents in your environment. Stop and smell the flowers. Our sense of smell is like a trained muscle, the more we use it, the stronger it gets!

Want to learn more about using essential oils? Check out my latest book Science of Essentials: The Essential Guide for Using Aromatherapy to Promote Health and Healing here.

Looking for more education on using essential oils for emotional health? See my blog article, The Best Essential Oils for Stress and Anxiety and 5 Tips for Using Aromatherapy for Stress Relief. 



Disclaimer: This blog is for general informational purposes only and does not constitute the practice of medicine, nursing or other professional health care services, including the giving of medical advice. The use of information on this blog or materials linked from this blog is at the user's own risk. The content of this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Users should not disregard, or delay in obtaining, medical advice for any medical condition they may have, and should seek the assistance of their health care professionals for any such conditions.


References:

  1. Varendi H, Porter RH, Winberg J. Does the newborn baby find the nipple by smell? Lancet. 1994 Oct 8;344(8928):989-90. doi: 10.1016/s0140-6736(94)91645-4.

  2. Kadohisa M. Effects of odor on emotion, with implications. Front Syst Neurosci. 2013 Oct 10;7:66.

  3. Herz, Rachel. The Scent of Desire. (2007). Harper Collins Publishers: New York.

  4. Lv XN, Liu ZJ, Zhang HJ, Tzeng CM. Aromatherapy and the central nerve system (CNS): therapeutic mechanism and its associated genes. Curr Drug Targets. 2013 Jul;14(8):872-9.

  5. Lizarraga-Valderrama LR. Effects of essential oils on central nervous system: Focus on mental health. Phytother Res. 2021 Feb;35(2):657-679.

  6. Watanabe E, Kuchta K, Kimura M, Rauwald HW, Kamei T, Imanishi J. 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. 2015;22(1):43-9.

  7. Buck, L. and Axel, R. (1991) Cell, vol.65, 175-187.

  8. Bartolomei F, Lagarde S, Médina Villalon S, McGonigal A, Benar CG. The "Proust phenomenon": Odor-evoked autobiographical memories triggered by direct amygdala stimulation in human. Cortex. 2017 May;90:173-175.

  9. Herz, Rachel. The Scent of Desire. (2007). Harper Collins Publishers: New York.

  10. Pluznick JL, Protzko RJ, Gevorgyan H, Peterlin Z, Sipos A, Han J, Brunet I, Wan LX, Rey F, Wang T, Firestein SJ, Yanagisawa M, Gordon JI, Eichmann A, Peti-Peterdi J, Caplan MJ. Olfactory receptor responding to gut microbiota-derived signals plays a role in renin secretion and blood pressure regulation. Proc Natl Acad Sci U S A. 2013 Mar 12;110(11):4410-5.

  11. Maßberg D, Hatt H. Human Olfactory Receptors: Novel Cellular Functions Outside of the Nose. Physiol Rev. 2018 Jul 1;98(3):1739-1763.

  12. Smith TD, Bhatnagar KP. Anatomy of the olfactory system. Handb Clin Neurol. 2019;164:17-28.

  13. Cameron EL. Pregnancy and olfaction: a review. Front Psychol. 2014 Feb 6;5:67.

  14. Oliveira-Pinto AV, Santos RM, Coutinho RA, Oliveira LM, Santos GB, Alho AT, Leite RE, Farfel JM, Suemoto CK, Grinberg LT, Pasqualucci CA, Jacob-Filho W, Lent R. Sexual dimorphism in the human olfactory bulb: females have more neurons and glial cells than males. PLoS One. 2014 Nov 5;9(11):e111733.


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