The Science of Scent: A deep dive into how scents can evoke memories, alter our mood, and why humans have such a profound connection to them.

Have you ever been whisked away to a distant memory by the mere whiff of a long-unforgotten dish? Or maybe that stranger’s perfume takes you back to those moments that you shared with that person you used to love so long ago. Explore the powerful science behind these olfactory experiences and understand why our brains are so deeply intertwined with the world of fragrance.

What is the Olfactory System?

The olfactory system is responsible for our sense of smell, and it is intricately connected to various regions of the brain which explains why scents can evoke strong memories and emotions. Olfactory sensory receptors and neurons, the olfactory nerve, and the olfactory bulb are the key parts of the olfactory system. When we inhale, odor molecules from the outside world enter our nasal cavity. If the odor molecules are strong enough, they will travel upward towards the olfactory epithelium, a specialized tissue that consists of hundreds of olfactory sensory receptors. If enough odor molecules bind to these receptors (i.e. if the odor is strong enough), the olfactory sensory neurons fire an electric signal that travels along the olfactory nerve towards our brain for processing. The fibers of the olfactory nerve lead directly to the olfactory bulb which is situated beneath the frontal lobe of the brain and is responsible for distributing the sensory information to other regions of the brain including the hippocampus (involved in memory) and the amygdala (involved in emotion). 

The Neural Interplay of Scent and Emotion

As part of our limbic system, the hippocampus and amygdala are integral structures of the brain that are crucial for memory formation. While the hippocampus is responsible for the formation, organization, and storage of memories, the amygdala assigns these memories with emotional significance. When an event is emotionally charged, be it positive or negative, the amygdala amplifies the strength of the memory consolidation process in the hippocampus. As a result, emotional memories tend to be recalled more easily. Given their connections to the olfactory system, the hippocampus and amygdala can quickly associate specific smells with particular memories and the emotions associated with those memories. This explains why certain scents can vividly trigger the evocation of our previous experiences. In a study led by psychologist Chelsea Reid, participants sampled 12 scents and rated the extent to which scent was familiar as well as the extent to which scents evoked nostalgia. Participants who measured high in nostalgia proneness reported more scent-evoked nostalgia, and the scents that elicited greater nostalgia were described as arousing, familiar, and autobiographically relevant. In addition, scent-evoked nostalgia was highly associated with positive emotions as well as social connectedness and meaning of life. This study by Reid reveals that certain scents can not only evoke strong feelings of nostalgia, but also associate with positive emotions such as high self esteem, optimism, and sense peace and purpose.

Oddly enough, I am very fond of the smell of sunscreen. Growing up on the coast of southern California, I spent just as much time at the beach as I spent at home. Catching a mere whiff of its tropical and floral notes transports me to my favorite sunset spot in Redondo Beach, California, right off of Avenue I at the Riviera Village. I almost feel the chilly waves crash onto my feet and the warmth of the bright orange sun soak my entire body. For a moment, it’s as if the sea breeze carries all of my responsibilities away and my worries go as tranquil as the horizon. I am in a total state of summer relaxation, untroubled. It’s funny how something as simple as sunscreen can evoke such vivid detail and strong emotion. 

The Science Behind Aromatherapy

Since the dawn of civilization, aromatherapy, the practice of using scents to enhance physical and emotional well-being, has been used to naturally restore the mind and body. In this practice, aromatic materials are harvested from various plants and flowers to be converted into essential oils and other fragrance components. But exactly how do natural oils and components enhance our wellbeing?

Like we have learned before, inhalation of odor molecules sends signals to our brain allowing us to interpret what we are smelling from the outside world. When we inhale the natural compounds from the essential oils, the odor molecules, as well as their beneficial properties, travel from the olfactory nerves directly to our brain and more specifically, the amygdala. Considering that the amygdala is responsible for regulating our emotions, our sense of smell can play a role in physiological effects of mood. In the past few decades, researchers have been conducting more scientific studies that examine the relationship between aroma inhalation and human brain functions. A study published in the National Library of Medicine examined the effects of a 3 minute aromatherapy session on 40 adults. Participants were either inhaling lavender aroma (considered a relaxing odor) or rosemary (considered a stimulant odor). The participants were also instructed to complete simple math computations before and after the session. Participants in the lavender group reported feeling more relaxed and performed the math computations quicker and more accurately following the aromatherapy session. On the other hand, participants in the rosemary group were only faster and not more accurate at performing the math computations. They also reported feeling more relaxed and alert and had lower state anxiety scores as well. A different study that examined the effects of jasmine oil inhalation on the function of the central nervous system and mood responses yielded similar results. The electroencephalogram (EEG), a method of measuring the spontaneous electrical activity of the brain, was assessed on twenty healthy participants before and after odor inhalation. In addition to EEG recording, participants were also asked to estimate their emotional responses. The results indicated that positive emotions such as feeling energized, refreshed, and alert increased by jasmine oil, while negative emotions such as drowsiness and stress decreased. In light of the studies mentioned, it is evident that the inhalation of specific aromas from essential oils has an impact on human brain functions, particularly in areas responsible for regulating emotions. These findings not only suggest that aromas, such that of lavender, rosemary, and jasmine, can serve as effective tools for promoting relaxation and enhancing mood, but also highlight the potential of aromatherapy as a non-invasive approach to improve cognitive function. 

The Power of Scent On Our Human Experience

While many of us have never realized, scents have a silent power over our emotions, memories, and even cognitive functions. The complex relationship between our olfactory system and brain paints a clear picture. Scents are not just passive experiences, but rather they actively shape our mood, transport us across time, and influence our mental performance. From the deeply personal memories evoked from a familiar aroma to the therapeutic applications of aromatherapy, the science of scent reveals the intricate ways our sense of smell is woven with our overall sense of self and wellbeing.

Sources

Diego, M. A., Jones, N. A., Field, T., Hernandez-Reif, M., Schanberg, S., Kuhnm C., McAdam, V., Galamaga, R., Galamaga, M. (1998). Aromatherapy positively affects mood, EEG patterns of alertness and math computations. International Journal of Neuroscience. 10.3109/00207459808986469

Reid, C. A., Green, J. D., Wildschut, T., & Sedikides, C. (2015). Scent evoked nostalgia. Memory.  http://dx.doi.org/10.1080/09658211.2013.876048

Sayowan, W., Siripornpanich, V., Hongratanaworakit, T., Kotchabhakdi, N. & Ruangrungsi, N. (2013). The effects of jasmine oil inhalation on brain wave activities and emotions. Journal of Health Research. http://www.jhr.cphs.chula.ac.th 

Sowndhararajan, K. & Kim S. (2016). Influence of fragrance on human psychophysiological activity: with special reference to human electroencephalographic response. Sci Pharm. 10.3390/scipharm84040724