Series in Aromatherapy, Part 2: The Sense of Smell

Scientific evidence has shown that the sense of smell has always been important to humans as well as animals. It has an impact on many aspects of our lives including our perceptions of others, potential mates, feelings and emotions, memory, behavior and even our health.

The sense of smell has always afforded protection by obtaining information from the environment A cave dweller, before leaving his home would have sniffed the air rather like a dog would do, checking for the smells of other people who may be dangerous, the smell of animals which may be killers, or any other smell which gave a sense of danger.

A good example of this protective function is our reaction to the smell of burning. For most people this will engender a feeling of fear or concern, which will promote a flow of adrenaline, which in turn will provide the fight or flight instinct to run away from the danger or to fight it.

‘Danger scents’ can be acrid, pungent, spicy, acidic, and burning. The fifth cranial nerve, which is the primary sensory nerve for the face, includes the nasal cavity. This nerve is triggered by danger smells causing heat and irritation in the nasal lining and acts as a protective backup to the olfactory system.

So what is the olfactory system, and how does it work?

Tiny smell particles travel inside the nose, which is full of nerve endings called smell receptors, and are caught in mucous. There are about 350 of these that are capable of categorizing smells and sending smell signals to the olfactory bulb in the brain. The olfactory bulb then relays a signal to the olfactory cortex. This in turn signals other brain areas which provoke memories, feelings and perceptions.

If the odor receptors experience a new smell, then the brain will file the feeling that was being experienced at that time. Later when that odor molecule is smelled again, the brain will remember the emotion that was felt at the time of the initial sniff.

If the odor receptor has encountered the smell before and the memory or emotion associated with it was a negative or stressful one then that smell will be unpleasant to the recipient. However, if the feeling experienced was a joyful one then it will engender pleasant memories.

The smell and taste of food can act in a similar way. During eating, most of the flavor tasted is coming from aromas the food gives off detected by smell receptors in the nose. Try eating with your nose held closed. You will notice a difference in the flavor than when your nose is open. That is why a head cold with a stuffed up nose will lessen the flavor of food.

Colds, flu or sinus infections can cause a long lasting condition called anosmia, which means no sense of smell at all. Phantosmia is when a smell is perceived but there is really none there. This can be caused by a brain tumor or migraine. Parosmia is when a real odor gives rise to a distorted perception. In most cases the smell perceived is bad.

The more aromas are used, the more research is carried out, and the more discoveries are made. University of Cincinnati has discovered that a poor sense of smell can be a diagnostic feature of Alzheimer’s and Parkinson’s disease. Another is that women have a better sense of smell than men do, especially when they are ovulating, which makes sense if smell helps a woman to choose a mate. Another is that dogs can detect the smell of cancer in humans. (New York Times report)

A recent study has shown that belief can alter our sensory perception and our physiological responses. For example, lavender is usually explained as having a sedating and relaxing effect. When people were told this in a scientific study, they did relax as measured by changes in heart rate and skin conductance. When told it had stimulating properties, the same measures showed that people were stimulated. (Sense of Smell Institute)

The professional therapist uses this knowledge to benefit clients. It doesn’t really matter whether the information they give comes from scientific evidence, anecdotal evidence, or personal observation. The main thing is that when the client is given a truly therapeutic experience coupled with an aroma which they believe will be helpful they will be helped.

Bibliography
The Nose Knows by Avery Gilbert.
Whiff by C.Russell Brumfield.
The Scented Ape by David M. Stoddart.
Learning to Smell by Donald A Wilson

Elizabeth McGinnes has been involved in Aromatherapy for more than 25 years and has a postgraduate qualification in clinical aromatherapy.