Understanding the mechanisms of olfaction is important to any of you who use aromatherapy, fragrances, or are interested in scents. It is also important to understand the chemical communication via pheromones so that you can best understand how you interact and respond to the environment and the people around you. Psychology also has a great impact on how we process scents.
How Olfaction Works
The body can distinguish around 10,000 different aromas (Liang, 2015). Olfaction works very simply. First, the smell enters the nose. Once inside, the scent gets dissolved in mucus, which then stimulates one or several of the twelve million olfactory receptor cells in the nose (Liang, 2015). The receptor cells, which sit high on the nasal cavity, send a nerve impulse to the area of the brain that processes the smell (BBC, 2014; Liang, 2015). They do this through Cranial Nerve I, which connects the olfactory receptor cells with the brain cortex within the temporal lobe (Liang, 2015). This same nerve also sends an impulse to the limbic system, which is the area of the brain related to emotions. This is why aromas affect emotions, and also why aromas and emotions are often linked together in people’s memories (Liang, 2015).
Many scents trigger Cranial Nerve V in addition to Cranial Nerve I, and this stimulates the trigeminal system (Heuberger, 2010). The trigeminal system handles mechanical sensations like itching and burning, as well as temperature sensations, such as warmth and coolness. What this means is that certain scents can bring about mechanical and temperature related responses in the body. For instance, smells can revive someone who has fainted, as well as increase heart rate, affect sleep, and impact performance and efficiency (Buckle, 2003; Heuberger, 2010). It is also believed that many scents are able to cross the blood-brain barrier and create different effects in the body such as arousal, although the exact mechanism of how this works is not yet understood (Heuberger, 2010).
In terms of the power of the olfactory system, it is worthwhile to note that those who have suffered from anosmia, or have lost their sense of smell, experience a sense of loss, stress, and depression when they take in a scent (Rhind, 2012).
The eventual perception of smell varies from person to person, and each individual interprets the smell in a different manner, whether positive or negative (Rhind, 2012). What smells good to one person may not smell good to another.
How Pheromones Participate In Olfaction
It is important to recognize that communication between two people does not just occur through verbal, vocal, and visual communication channels, but also through chemical and olfactory ones. Certain scents can seem attractive when you are with someone, and no longer seem attractive when that person is no longer there.
Pheromones are “airborne chemicals involuntarily expelled into the air that affect the physiology or behavior of other members of the same species” (Buckle, 2003, p. 103). Every person emits a unique smell, and these smells arise mostly from the pubic and axillary areas of the body, although axillary odor seems to be the main source of pheromones (Buckle, 2003; Lis-Balchin, 2006). When one person releases pheromones, those around them perceive the scent through the same communication channels as any other smell, but the reaction it creates varies greatly from individual to individual. In fact, the sensing of pheromones starts in babies even 3 days after being born when they recognize their mother’s smell (Lis-Balchin, 2006). At that stage, babies begin to prefer their mother’s scent to that of other mothers. This perception of pheromones in other people continues throughout our lives, and influences the partner we choose to have a relationship with (Lis-Balchin, 2006). It is believed that the likeness of pheromones between two people is so strong that when couples separate, the smell that once used to attract them to each other no longer does (Buckle, 2003).
How Psychology Influences Smell
There are several variables that have a psychological effect on a person and can impact how they react to a particular smell. Some of these are aroma association, conditioning, response bias, placebo effect, and expectations. Collectively, the study of how odors have a psychological effect on a person is called aromachology (Rhind, 2012). Aromachology is concerned with the temporary effect of all types of scents and odors, whether natural or synthetic. Each scent creates a unique and different response on an individual, given that reactions to scents and aromas are subjective (Petersen, 2014). Warren and Warrenburg (1993) classified the possible responses as positive, bringing about sensations of happiness, sensuality, relaxation, and stimulation, or as negative, bringing about sensations of stress, depression, and apathy (Lis-Balchin, 2006).
Aroma association deals with the impact of a person’s perception on the physiological and psychological response they have to a smell. Often these associations elicit a positive response (Petersen, 2014). For instance, many associate the smell of pine with being outdoors and in the woods, and certain furniture stores that sell wood-made items use a pine scent in their stores to encourage sales (Lis-Balchin, 2006). Aroma associations can also be based on lifestyle and culture. For instance, the same citrus smell in Europe was stimulating and in Japan calming, while the same floral smell in Europe was calming and in Japan stimulating (Petersen, 2014).
Conditioning relates to the negative effect that an aroma creates on a person. Odors create emotional memories, and these create an impact on how they are experienced (Rhind, 2012). For example, when a person senses an aroma when they are under stress, the next time they smell the same aroma they may feel similar symptoms of stress (Petersen, 2014). Buckle (2003) described a situation where a man was afraid of a teacher who wore a particular scent, and at age 55, he still suffered from fear and anxiety whenever he smelled that perfume.
Response bias is based purely on a person’s previous positive or negative experience with a smell (Petersen, 2014). It may be that they encountered a smell in the past that they did not like or that they had a negative experience with, and they will continue to associate that scent with that experience when they smell it in the future. For example, if a person fell ill in a room that was scented with lavender, every time they smell lavender in the future, they will consciously or unconsciously remember how they felt when they were sick and dislike the lavender scent. A response bias can also happen if the person had a positive experience with the smell, and if they smell it again, they will respond positively (Petersen, 2014).
The Placebo Effect
The placebo effect has to do with the power of suggestion and mind over matter (Lis-Balchin, 2006). For example, when a person is told that a scent will affect them in a particular way, they believe it, and as a result of this belief they experience the scent in the way they were told (Rhind, 2012). If someone is told that they will feel relaxed when they smell German chamomile, when they encounter the smell, their bodies will physically calm and relax. Lis-Balchin (2006) says the placebo effect has been found to relieve post-operative pain, bring about sleep, improve mental awareness, alleviate chronic diseases, and decrease the size of warts, among others. The placebo effect can have positive reactions like these, but they can also have negative reactions, such as nausea, headaches, and allergic reactions (Lis-Balchin, 2006). It all depends on what the person is told the scent will do.
Expectations is similar to the placebo effect, but instead of a person being told that a particular effect will occur, the person brings an expectation themselves of how they will feel when they sense the aroma. For instance, if they feel that a particular essential oil will have a positive effect, such as essential oil of Roman chamomile helping them sleep, then they may look forward to that effect taking place, and thus create the experience. They will look forward to a good night’s sleep when they smell Roman chamomile essential oil before going to bed, and in fact sleep well. It is not that the essential oil is not effective, but the expectation of how they should feel creates a strong impact on them (Petersen, 2014).
Olfaction relates to the science behind how smell is perceived by the body and the signaling that happens between the aroma being perceived in the nose and the eventual response the person has to the scent. Chemical communication via pheromones is perceived just like any other aroma, but it has profound effects in the body because they are awakened in us since we are babies. As we grow and mature, several psychological factions can also affect how we perceive scents and smells.
BBC. (2014). Nervous system- smell. BBC Science: Human Body & Mind. Retrieved on October 7, 2016 from http://www.bbc.co.uk/science/humanbody/body/factfiles/smell/smell_animation.shtml
Buckle, J. (2003). Clinical Aromatherapy: Essential Oils In Practice (2nd ed.). London, United Kingdom: Churchill Livingstone.
Heuberger, E. (2010). Handbook of Essential Oils: Science, Technology, and Applications. Husnu Can Baser, K. & Buchbauer, G. (Eds.) Boca Raton, FL: CRC Press.
Liang, B. (2015). The Sense of Smell. General Anatomy & Physiology. Retrieved on October 7, 2016 from http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP14004
Lis-Balchin, M. (2006). Aromatherapy Science: A Guide for Healthcare Professionals. London, United Kingdom: Pharmaceutical Press.
Petersen, D. (2014). Olfactory science and psychological activities. ACHS Aroma 501, Aromatherapy Science. Portland, OR: American College of Healthcare Sciences.
Rhind, J.P. (2012). Essential Oils: A Handbook for Aromatherapy Practice (2nd ed.). London, United Kingdom: Singing Dragon.