The ability to smell provides many advantages. In addition to driving pleasure from pleasant fragrances, it adds multiple layers to any meals consumed. The taste buds along the tongue provide information on the food’s basic tastes, but the rest of the unique flavors are experienced through the involvement of smell. Beyond fuller enjoyments of culinary delights, a functional sense of smell can act as a valuable source of safety. Gas leaks can be detected by scent, for instance, allowing for the problem to be amended or the area to be vacated.
Those who do not enjoy the full benefits of their sense of smell are not without hope, however, as research points to smell training as a valid way of building the ability to smell. Persistent anosmia-an inability to smell that does not ease overtime-may be countered with a type of odor therapy, research has shown.
How Humans Smell: Structure and Process
Approximately 1,000 genes code for olfactory receptors, a discovery brought to light in 1991by Linda Buck of the Fred Hutchinson Cancer Research Center and fellow laureate Richard Axel of Howard Hughes Medical Institute.
Much understanding has been gleaned by the research of Buck and Axel, supplemented with further research on fruit flies and which receptors for those insects detect which types of odors. Among humans, Buck and Axel’s findings provided the basis for the commonly held understanding of how humans smell odors.
Like other senses such as touch and sight, smelling involves interacting with the particular subject-in this case, an odor-and having it be processed by receptors and the brain.
When breathing in a particular scent, odor molecules in the air get inhaled into the nasal cavity. In this nasal cavity is the olfactory mucosa; here can be found-among other cells-axons from olfactory neurons. This area in the nasal cavity makes up the first step in the olfactory pathway, allowing odors to be detected.
With those scented molecules inside the nose, their presence stimulates or inhibits different receptors, which fire off a signal to the olfactory bulb, an area just under the brain. It is the olfactory bulb that tells the brain the nature of the odor that was inhaled. That scent may be one of the 10,000 humans are capable of interpreting.
While the outside of the nose bears a simple structure-two nostrils, a bridge-the interior is made up of different areas, from hollow sections known as cavities, to punching bag-shaped protrusions called turbinates. Each serves its own unique purpose in maximizing the functionality of our nose. The sinuses produce mucus that moisturizes and protects from pollutants and other airborne particles like dust and pollen; it additionally serves the subtler purposesof lightening the skull and improving voices. Additional filtering is achieved through turbinates, along with humidifying and warming. No one enjoys the feeling of a cold, stiff inner nose.
Loss of Smell
Airborne particles or trauma can disrupt the functionality and structure of the inner nose, and thus debilitate the sense of smell.Deviated septums are common afflictions at varying extents. Almost everyone has a very slightly uneven septum, which occurs when the area separating the left and right nostril is not right in the middle, favoring one side or the other. For those with light versions of this, the most this would mean is brief moments of uneven breathing through the nose in the morning when noses function at their worst.
But more extreme cases exist in plentiful numbers and cause plentiful damage, including severely impairing or completely preventing the ability to smell odors. This is due to the obstruction of airflow, preventing scented particles from reaching the olfactory bulb for processing. Deviated septums can be the result of trauma to the nose at any point in life, or they can be a trait at birth from improper development.
Prolonged congestion and blockage by masses in the nose prevent proper smelling as well. Nasal polypsare noncancerous masses within the nose and sinuses that inhibit airflow. They can occur naturally, or as the result of sinus infections, allergic rhinitis (hay fever), sinusitis, chronic infections, and even cystic fibrosis. Sometimes which exact reason can be difficult to pinpoint, but the end result can include the inability to smell, which presents problems of its own.
Certain medications or inhalation of harmful odors also contribute to not being able to smell.
Researching a Resolution
There are many causes of persistent anosmia and many degrees of anosmia itself. But a prolonged inability to smell anything presents unique hurdles when navigating ways to amend it. These challenges drove researchers to find out how to help those with anosmia.
Much like the sense of sight, the sense of smell requires a learning curve. Radically new corrective glasses take time to fully help the eyes see their best; the eyes and brain need to “learn” this new skill the lenses have given them: sight. Such is the case with prolonged anosmia.
A 2009 study by Professor Thomas Hummel observed the effects of short-term, repeated exposure to different odors on those with anosmia. A major area of interest for Professor Hummel, who also runs the Smell and Taste Clinic at the University of Dresden, was parallels between scent and taste. Foods are grouped into categories of taste: sweet, salty, sour, bitter, and umami. These five categories cover the flavors experienced when different foods are tasted.
Professor Hummel wondered if the same could be done with scents. His ultimate results led him to categorize scents into four types: flowery, fruity, spicy, and resinous. He felt any odor inhaled could fall under one of these four groups, making them key in the development of olfactory rehabilitation. Using this knowledge, he compared two groups of individuals with anosmia; one group was given carefully selected essential oils to sniff at scheduled times across 12 weeks, while the second group did not smell the oils.
30% of the test group experienced improved abilities to smell that had previously been nonexistent. This included individuals whose anosmia was caused by a variety of sources, from head trauma to respiratory infection.Professor Hummel’s work became the basis for further research, including a 2015 study at the Istanbul Surgery Hospital found that the improvement in smelling ability could increase if the regimen was followed beyond 12 weeks.
The Smell Training Regimen
To represent each of the four main fragrances, Hummel’s study utilized four essential oils for participants to sniff. They were:
- Rose for flowery
- Lemon for fruity
- Cloves for spicy
- Eucalyptus for resinous
Thus, to replicate smell training, it is advised that participants use small jars of these essential oils. Those hoping to heal their depleted sense of smell would hold the opening of each jar near their nose one at a time, and breathe in. That inhale should be normal and not exaggerated; when the nose is cleared (sinuses drained, deviated septum straightened, etc) odor molecules will find their way to the olfactory lobe, and even if the passage is not completely clear, exaggerated breaths will not yield any benefits, only dizziness.
The process should be repeated for each fragrance a few times, with five minute rests in between. Just as Professor Hummel and the subsequent 2015 study found: repetition is an immensely helpful tool. A pair of glasses is not discarded after the first time they are put on and vision requires adjusting. Likewise, the nose and olfactory neurons need exposure and exercise; the way to provide that is by exposing them to these core scents at repeated, scheduled increments across multiple weeks.
Training the nose in such a fashion is similar to training expert perfumers undergo; a university in France is renowned for the rigorous training its pupils go through to be masters of fragrance. If there is ever the worrying realization that the sense of smell is not what it used to be-or should be, if it was never really there-methods exist to build it up and heal it, just like muscles. Conquering this opens up a whole new world of sensations-and opens up the nose to some delightful odors