Sensory perception across the lifespan
18 Taste and smell disorders
Normally, most individual variation in the sensitivity to smell and taste lies within the normal biological range. However, a low sensitivity to taste or smell becomes a problem if it affects your health and/or well-being.
In The Netherlands, an estimated number of 250.000-300.000 people suffer from smell and/or taste disorders. Taste and smell dysfunctions can be inborn or due to trauma, disease or medicine use. For example, certain medication affects saliva production or epithelial cells in the oral cavity. It may also be that brain trauma causes taste phantom sensations, these are sensations while the actual stimulus is not present. An example are patients with Burning Mouth Sensations, these people experience very intense somatosensations (i.e., touch, temperature, pain/burn) 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 is even recognized one of the diagnostic criteria for infection with the virus. How COVID-19 changes taste and smell exactly, remains unknown. 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 taste through the loss of smell).
In the short video below, Dr. Elbrich Postma tells you more about smell and taste loss in her talk “How to taste with your nose”
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, 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, 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, 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, influenza, common cold), smoking, diabetes, B12 or zinc deficiency, stroke. |
| Hypogeusia | Reduced sense of taste | Aging, allergies, viral infections (COVID, 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, head and neck cancers, tongue inflammation, pregnancy etc.). |
CASE – 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, the sense of smell can work regenerative, and smell training has emerged as a promising therapy to help recover this lost sense. This method involves regularly sniffing a set of different odors, like essential oils or spices, to stimulate the olfactory system. This regenerative function of the smell system is due to its 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 colors or shapes with specific smells, to improve odor 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.
See this link for more information about the treatment of smell disorders.
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.