Olfaction, the sense of smell,
allows us to
When this function is altered, we may find a broad spectrum of conditions:
Anosmia refers to the total loss of smell function: you cannot perceive odorants.
Congenital anosmia is defined when you are born without the sense of smell. It is a rare condition that comes alone or, often, in association with other congenital disorders (for example Kallmann Syndrome and Charge syndrome).
Iposmia is the reduction of olfactory function – you may, for example, smell odors as less “intense” or need higher odorant concentration to sense them.
Parosmia is the alteration of odor perception. Odors become “strange”, and smell different. For example, flowers smell like soap, coffee feels metallic, etc.
Cacosmia, it is a form of parosmia that turns more into disgusting odors, things stink, and food and beverages smell off without apparent reasons: meat smells like garbage, coffee or flowers smell like rotten eggs, etc.
Phantosmia refers to olfactory hallucinations and when you smell odors that are not really around you. It might be associated as well to aura episodes before migraine and seizure episode in epilepsy.
Trigeminal refers to sensations depending from the nerve endings of the trigeminus nerve. Some branches of this nerve are located in the nose, in the tongue and in the oral cavity carrying irritant sensations. They are responsible for the “freshness” of menthol, the burning feeling of chili pepper (capsaicin) or mustard, etc. If you have anosmia or olfactory alteration you may still be able to perceive such stimuli.
Flavour refers in common sense to “taste”-sensation, but it is not: it is a perception coming from the contribution of smell, taste and trigeminal, plus feelings coming from textures and temperature of the food and beverages in the mouth. For this reason, when we cannot smell well we have the feeling of flavor /taste loss.
Taste is the sensation in the mouth evoked by basic tastants: bitter, sweet, salt, sour, umami/savory.
Why it happens?
Aside congenital anosmia, olfactory alterations may occur for several reasons. In adults the most common might be divided in three subgroups:
Viral infections (flu, Covid-19, etc.), inflammations, cold, rhinosinusitis, polyps, etc. In such cases, usually there is a combination of factors:
Nasal occlusion: the air passages in your nostrils (one side or both) are totally or partially occluded by congestion, polyps, etc., therefore air and odorants cannot reach the olfactory receptors.
Inflammation of the olfactory region.
Virus and pathogens damaged directly the olfactory sensory neurons or other cells in the olfactory epithelium – the nasal region that detect the odors.
Head trauma, accidents and injures that cause a damage to olfactory nerves – the connection between olfactory area in the nose and the brain – or brain trauma involving areas responsible for odor recognition and smell perception.
Neurodegenerative diseases, Alzheimer and Parkinson disease, or dementia are often presented with smell loss or smell reduction.
Moreover, aging presents often smell reduction.
Sometimes, before or after a period of anosmia, people experience episodes of parosmia or phantosmia. It is very common after Covid-19 or other viral infections, but it might happen after trauma (rare) or surgical operation (polyps remotion, etc.) as well. Scientists cannot yet fully explain the phenomenon, but they suggest it may occur when the olfactory region in the nose is regenerating and the process is not yet fully complete: olfactory receptors may not have been correctly replaced, only partially, or not properly reconnected to the olfactory areas in the brain.
What to do
People with smell and taste disorders feel often lonely, they encounter difficulties explaining feelings and sensations, and find poor information and direction on what to do.
Therefore, the first action to help anosmics is listening to them, not minimize their condition and support them in their search and quest for assistance.
At the moment unfortunately there is no cure for anosmia and olfactory alteration.
Depending on what is the cause of the alteration, the extension of the lesion and other clinical conditions the prognosis may vary.
In many cases, for smell loss due to inflammation or other infections, it is used a corticosteroids therapy, sometimes it is possible to solve obstructive problems with surgical operation, and in such cases often olfaction recovers.
In other situations, recovery might still be possible but is variable, it requires usually long time – from weeks to months, even years - and is not always predictable.
Accepting and dealing with sensory changes and smell alterations may cause discomfort, distress, alteration in eating behavior and emotional pain. In these cases, psychological support may help to face and adapt to the new situation.
If you experience or notice a reduction or change of your sense of smell for more than three weeks, experts suggest to visit a doctor, possibly an ENT who specializes in smell and taste. He will be able to conduct a proper examination and evaluate specific needs and possible treatments.
The scientific community have collected some evidences that olfactory training, might help accelerating the recovery process in some cases, mainly after viral infection and similar diseases.
Olfactory training should be considered not a cure, as it does not ensure smell recovery, but a sort of physiotherapy for the nose. According to scientists the main hypothesis is that olfactory stimuli might promote locally the regeneration of the olfactory receptors, while in the brain it might help reinforcing and “rewiring” the cognitive pathway that allows to remember and to discriminate odors.
The olfactory training consists in a daily routine smelling 4 odors (for example: roses, eucalyptol, cloves, lime/lemon) twice a day. While smelling, it helps trying to visualize the source of scent (roses, fruit, etc.), and keep track and notes of feelings, sensations and any progress or perception. The training should last for at least 4-6 weeks.
Note: the origin and source of the odors used for the training is NOT important. There are no scientific evidences that a specific odor or how it is made makes any difference. Usually, it is suggested to use essential oils because they are more practical and they last long, but you can start with any odor you prefer.
Find here below some Institutions and associations who specialize in smell and taste, and support patients with taste and smell alterations.
Charity e no-profit