Sensory perception across the lifespan
18 Taste and Smell Disorders
Normally, most individual variation in the sensitivity to smell and taste lies within a normal biological range; however, a low sensitivity to taste or smell becomes a problem if it affects your health or well-being.
In the Netherlands, it is estimated that about 300.000 people suffer from smell and/or taste disorders[1]. Taste and smell dysfunctions can be inborn, due to trauma or disease.
Brain trauma may cause taste phantom sensations; these are sensations while the actual stimulus is not present. An example is patients with burning mouth sensations, who experience very intense somatosensations (i.e., touch, temperature, pain/burning) without the stimulus being present.
Another well-known example of a condition affecting smell and taste is COVID-19. The loss of smell and taste was even recognised one of the diagnostic criteria for infection with the virus. How COVID-19 changes taste and smell is not exactly known. The virus seems to affect cells supporting the olfactory nerve. This can block the signals going from this nerve through the brain, causing loss in smell (and of taste, through the loss of smell).
And last, certain medication affects saliva production or epithelial cells in the oral cavity. For example, cancer treatment that affects cells with rapid turnover such as taste receptor cells.
Table 5 shows the types of taste and smell disorders, as well as some possible causes. On this site, you can look up the taste and smell disorders and see the full overview of causes and implications. In Video 9, the impact of taste and smell alterations on eating behaviour is further explained.
Table 5. Types and Causes of taste and smell disorders
Below a table in which the types of taste and smell disorders are noted, as well as some possible causes. On this site, you can look up the taste and smell disorders for all the causes and implications.
| Disorder | Meaning | Possible Causes |
| Anosmia | Loss of sense of smell | Viral infections (COVID-19, influenza, common cold), nasal polyps, allergies, Alzheimer’s disease, brain tumors, Multiple sclerosis (MS), high blood pressure, head trauma, obesity. |
| Hyposmia | Reduced sense of smell | Viral infections (COVID-19, influenza, common cold), nasal polyps, allergies, hormonal imbalance, Alzheimer’s disease, brain tumors, high blood pressure, head trauma, obesity. |
| Parosmia | Distorted sense of smell | Viral infections (COVID-19, influenza, common cold), head trauma, use of medication, smoking, cancer/cancer treatments. |
| Ageusia | Loss of sense of taste | Allergies, high blood pressure, medication, oral health conditions, viral infections (COVID-19, influenza, common cold), smoking, diabetes, B12 or zinc deficiency, stroke. |
| Hypogeusia | Reduced sense of taste | Aging, allergies, viral infections (COVID-19, influenza, common cold), dental issues, diabetes, diseases of the endocrine system, B12 deficiency, smoking, head trauma. |
| Dysgeusia | Distorted sense of taste | Aging, medication, poor oral hygiene, dental prosthesis, tobacco use, medical conditions (such as COVID-19, head and neck cancers, tongue inflammation, pregnancy, etc.). |
Video 9. “How to taste with your nose” by dr. Elbrich Postma
Example 5 – Smell Training
During the pandemic, many people (partly) lost their sense of smell due to COVID-19. These symptoms can linger for a long time, as up to four years later people still suffer from a decreased or lost sense of smell.
Luckily, smell training has emerged as a promising therapy to help recover this lost sense. This method involves regularly sniffing a set of different odours, like essential oils or spices, to stimulate the olfactory system. This effect is possible due to the unique ability to regenerate sensory neurons.
However, smell training requires patience, as it can take months to see improvement, and not everyone benefits from it. Researchers are exploring ways to enhance its effectiveness, such as using cross-modal associations.
Cross-modal associations occur when sensory cues from different systems are matched. This approach influences the brain’s ability to link sensory cues from different senses, like associating colours or shapes with specific smells, to improve odour perception and recognition. These associations significantly influence how we process sensory information, especially in the sense of smell.
Despite the challenges, ongoing research offers hope for those affected by anosmia, aiming to refine smell training techniques and help more people regain their sense of smell.
This link gives specific information on smell loss due to Covid-19, how it can be treated and why these treatments can help recover smell loss.
- https://www.knomc.nl/en/symptomen/loss-of-smell-and-taste/ ↵
The somatosensory system is touch or tactile perception. It is a network of neurons that help humans recognize objects, discriminate textures, generate sensory-motor feedback and perceive temperature differences.
The olfactory nerve is the first cranial nerve (CN I). This nerve enables the olfactory system and sense of smell. Through this nerve, information from olfactory receptors travels to the brain.