The sense of smell continues to be absent from routine examinations and this may be delaying diagnoses of serious neurodegenerative diseases. Complexity of this important sense makes it difficult to create the ideal test.
Smell continues to be, for many patients and even for a large part of healthcare systems, the forgotten sense of modern medicine. In a routine visit, it is normal to evaluate vision, hearing, and several more basic physical indicators, but rarely does a doctor systematically test the ability to smell.
Researchers and clinicians say that this gap is no longer a detail: it could mean the loss of an opportunity to detect diseases earlier neurodegenerative diseases, respiratory infections, exposure to pollutants and other relevant changes in our body.
Valentina Parma, from the Monell Chemical Senses Center, in the United States, argues that the olfactory function should be assessed in health examinations in the same way as blood pressure is measured.
Socially, the sense of smell continues to be socially undervalued, which does not help its introduction in medical examinations. Many people view it as the least important of the senses, especially when compared to sight or hearing. Even during the COVID-19 pandemic, when it became one of the most discussed symptoms, studies showed that the public continued to place a relatively low value on it. In one in particular, one in four university students even said that they I would do without my sense of smell rather than my cell phone.
Smell is essential for detecting environmental dangers, such as gas leaks, spoiled food or smoke, but it also strongly influences nutrition, daily pleasure and mental health. The loss of this sense may even be one of the first signs of serious illness.
For years, loss of smell has been associated mainly with intuitive and relatively common causes: colds, respiratory infections, allergies, nasal polyps, deviated septum, exposure to tobacco or alcohol, head injuries, nerve injuries, strokes, certain medications, hormonal changes or nutritional deficits.
In all these cases, the problem may arise due to interference in the path between the odorant moleculethe receptors in the nose and the way the brain interprets this information.
But over the past two decades, several researchers have begun to realize that loss of smell is not just an accessory consequence of some neurological diseases: in many cases, it seemed to precede them. In people later diagnosed with Alzheimer’s disease, Parkinson’s disease or multiple sclerosis, decreased sense of smell occurred years before the appearance of more visible symptoms, such as motor or cognitive changes.
The most consensual explanation is that, as these neurodegenerative diseases evolve, they first target brain areas involved in olfactory processing, before affecting centers associated with speech, cognition or movement. For some experts, this sequence gives the sense of smell a potential early warning value that medicine is not yet taking advantage of.
Another problem is that most people do not easily realize that they are losing their sense of smell, especially when the change is gradual. According to experts cited in the original text, many patients only truly notice the loss when it is practically total. And they also tend to be poor judges of their past and present olfactory abilities.
Of course, most people with (partial loss of smell) will not necessarily develop dementia or Parkinson’s. The usefulness of the test, argue the experts consulted by Jstor, would be less in its isolated diagnostic capacity and more in its value as a another sign to take into account. Just as high blood pressure does not in itself confirm a specific disease, a change in smell can act as cheap, simple and repeatable information, combined with age, risk factors, clinical history and other tests.
The COVID-19 pandemic has radically changed the visibility of this debate. When it became clear in 2020 that sudden loss of smell was one of the most characteristic symptoms of the first variants of the virus, public health began to look at smell more pragmatically. But this bet lost prominence when swab and saliva tests became more common.
Despite this, some scientists did not forget and investigated this area, which continues to be full of obstacles.
Contrary to what happens with measurements such as blood pressure, there is no single simple stimulus that allows everyone to be assigned an easily comparable absolute value. The perception of odors depends on several molecules, concentrations, detection thresholds and individual differences. Furthermore, people may not lose their sense of smell uniformly: they no longer recognize some odors, detect others in a distorted way or only maintain certain olfactory notes.
This complexity makes it difficult to create an ideal test. The exams considered best use several different odors, concentrations and tasks and require time, resources and practice to be administered. On the other hand, most health systems are not prepared to incorporate this type of assessment.
Some experts, despite acknowledging all this, also question the usefulness of regular smell tests outside of groups at risk of neurodegenerative diseases: including these tests in everyone’s routine check-ups could lead to anxiety in patients whose loss of smell will never evolve into something more serious, they argue.
