Beyond Fragrance: Unraveling the Secrets of Our Primal Olfactory Sense

Our olfactory sense is far more powerful than you might realize. It is commonly thought that the human sense of smell is much weaker than other land-based animals such as dogs. But, according to modern scientific research, humans have a profoundly established olfactory sense. 

Olfaction is our most primal way of interacting with the world. It is what shaped our reptilian brain and affects our cognition and behavior in every moment of our lives. Consciously – and subconsciously – humans are constantly taking in information from the world around them through olfaction. Some smells are more apparent than others, like brownies baking in the oven, the scent of fresh rain, or the aroma of a bouquet of Roses. But there are also odorless compounds that we often inhale that affect us in many ways. 

The sense of smell impacts how we think, feel, and act, and influences us on a deep physiological level. In this blog post, you will learn about how the sense of smell works, the connection between the olfactory sense and the brain, and how the sense of smell impacts almost everything we think, feel, and do.

The olfactory system is composed of the nose and nasal passages which are lined with mucous membranes, as well as the olfactory nerves, bulb, and tract. At the top of the nasal cavities, there is a membranous structure called an epithelium that contains millions of olfactory receptor cells. Tiny cilia extend out from these cells to cover the surface of the epithelial tissue. This is where there are receptor sites for aromatic molecules – which are responsible for initiating the ability to smell. The cilia are covered in a layer of mucus, and when an odorant molecule dissolves into the layer of mucus, it reaches a receptor site.

The receptor sites transform chemical molecules in the air into an electrical signal and transport that signal via the olfactory bulb and olfactory nerve to the brain. The olfactory bulb is a processing center, and the olfactory nerve carries sensory stimuli to the brain.

When we smell something, the receptor sites, and olfactory bulb essentially take a snapshot of the molecular pattern to be processed and understood by the brain. Humans have about 350 genes for receptor sites in the nose for detecting aromas. Aside from within the nasal cavity, there is also receptivity for scent in the back of the throat and through the trigeminal nerve [1].

The level at which we can detect a scent is called “detection threshold,” and humans have an incredible capacity for this. A good example of this is our ability to detect the smell of a natural gas leak. What we know to be the smell of gas is actually an additive called mercaptan –  which is an odorant added for safety measures. Without mercaptan, natural gas would be scentless. Amazingly, people are able to detect this odor at a level of 0.2 parts per billion, which is greater than a machine is able to detect [1]. 

Our ability to track smells is also magnificent. In a study conducted by Dr. Noam Sobel, a professor of neurobiology in the department of brain sciences at the Weizmann Institute of Science, an odorant was applied to a piece of string and buried under grass. They blocked the other senses of participants by blindfolding them, blocking hearing and putting gloves on. They asked the participants to locate and follow the scent, and found that the participants accurately followed the buried string by tracking the scent. The study also found that we are able to improve our capacity to smell, as participants improved in their ability to track the scent as the experiment went on [1]. 

The nose is a direct pathway to our brain. Olfactory sensory neurons at the top of our nasal cavity are the only place in the body where our brain (olfactory neurons) meets the outside world [1]. Sensations of smell journey instantly to the limbic system in the brain, which includes the hypothalamus, amygdala, thalamus, and hippocampus. The hippocampus is connected to memory and the amygdala is a major site for emotional processing. The hypothalamus produces neurotransmitters that impact our mood, as well as regulates our autonomic nervous system and governs our natural flow of breath. It is also the beginning of various hormone pathways, including the thyroid gland, reproductive system and the adrenal glands. 

In this way, the sense of smell has an influence on our endocrine system and hormones. An example of this is kallmann syndrome, which is hypogonadic development in male bodies that can prevent or delay puberty. Almost every patient with kallmann syndrome also has anosmia [1]. This conveys the intimate link between olfaction and the reproduction system in the body. 

Surprisingly, something doesn’t even need to have a perceivable scent in order to impact our behavior and hormones. In an odd study run by the Weizmann Olfaction Research Group, it was discovered that sniffing womens’ tears lowered free testosterone levels in men. Although there is no scent of the tears, our olfactory sense can detect the pheromones. It was also noted that smelling the tears could lower aggression in men [1]. This was equally true in a study with mice, where the tears of young mice were collected, and would effectively lower aggression rates in the adult male mice who sniffed the tears [1]. 

Our olfactory sense impacts our physiological, emotional and psychological functioning in every moment. Dr. Sobel noted that the loss of sense of smell is one of the earliest signs of neurodegenerative diseases such as Alzheimer's or Parkinson's [1]. 

At birth, olfaction is not tested in infants, unlike vision and hearing. Being born with a defective sense of smell is called congenital anosmia, and on average, it is not actually diagnosed until people are 14 years old [1]. Congenital anosmia impacts a person greatly, and can affect social contact, reduce romantic social contact, and even shorten the span of life for a person [1].

Without realizing it, when we shake hands with someone we are meeting for the first time, we are processing information about that person via their scent. This includes perceivable body odors and pheromones which are scentless. Throughout any given day, we are constantly smelling ourselves and others. When you instantly “click” with another person, it could have something to do with having a similar body odor. 

In another experiment done at the Weizmann Institute of Science, an “electronic nose” predicted whether or not people who have a similar odor would click more. In the experiment, people were not allowed to speak to one another, but were directed to stand  face-to-face (close enough so that they could smell one another) and mirror each other's movements. Participants would then keep switching partners and mirroring movements. Afterwards, they were asked to rate each other on how nice they thought each person was, who they thought they would be friends with, etc… and found that in fact, the people who smelled similar both thought each other would be more likely to be a nice person and a good friend [1]. This shows that although people may instantly “click” as friends based on similar interests or personality types, there could also be something happening at a deeper level in connection with scent.

When we start to realize how important and powerful the sense of smell is to our health and behavior, it becomes easy to appreciate aromatic medicine. Plants have the ability to shift and support our cognitive process and heal us on many levels through the sense of smell. Our body’s ability to take in and process information from the environment through olfaction is seemingly magic, and all of the research being done now is verifying what ancient peoples have already known. 

Cultures around the world have revered olfaction as the highest sensory form, and through modern research, it is clear to understand why. The sense of smell is a gateway to the subconscious mind, where great healing can unfold. Plants are intelligent, sensitive beings who can act upon the body, mind and emotions and serve as a healer, teacher and guide. Beyond what can be proven in a lab, there is something truly sacred about our relationship with the botanical kingdom. 

Aromatic plants can bring balance to all aspects of ourselves, from physical to subtle, and have the ability to touch the soul. They remind us to pause, take a deep breath and return to presence. The healing potential available to us through aromatic medicine is truly boundless, as it supplies us with the keys to unlocking our physical, mental and emotional wellbeing and can also connect us to the divine.

Article Written By Dawn Gibson

1. Huberman Lab Podcast. (2023). Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior.

© 2023 The Northwest School of Aromatic Medicine. All rights reserved.

*The statements above have not been evaluated by the FDA, and are for educational purposes only. This article is not intended to diagnose, treat, cure, or prevent any disease. This article should not be taken as medical advice. Please consult your physician before you use this information for health purposes.