Materiały źródłowe

• #1 You can train your nose – and 4 other surprising facts about your sense of smell

  https://theconversation.com/you-can-train-your-nose-and-4-other-surprising-facts-about-your-sense-of-smell-245366

  Smell often goes under the radar as one of the least valued senses. But it is one of the first sensory systems vertebrates developed and is linked to your mental health, memory and more. […] You can lose your ability to smell due to injury or infection for example during and after a COVID infection. This is known as olfactory dysfunction. In most cases its temporary, returning to normal within a few weeks. […] But following a COVID infection some people might continue to experience a loss of smell. Studies suggest the virus and a long-term immune response damages the cells that allow the olfactory system to regenerate. […] Around 5% of the global population suffer from anosmia total loss of smell. An estimated 15-20% suffer partial loss, known as hyposmia. […] Losing your sense of smell is shown to impact your personal and social relationships.

• #1 Olfactory System Guide: Sensory Dysfunction Explained

  https://cyranotherapeutics.com/sensory-dysfunction/

  Disruptions in the olfactory system can occur at various levelsanatomical, cellular, or molecular. […] These dysfunctions can manifest as a diminished or altered sense of smell, a condition known as anosmia or hyposmia. […] The impact of olfactory dysfunction goes beyond the sensory experience. It can signal broader health issues and significantly diminish quality of life by affecting taste perception, emotional well-being, and safety awareness.

• #1 Anosmia – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK482152/

  Anosmia is the inability to perceive smell/odor. It can be temporary or permanent and acquired or congenital. There are many causes. Neurological causes can include disturbances to the sensory nerves that make up the olfactory bulb or anywhere along the path in which the signal of smell is transferred to the brain. From the olfactory bulb, the signal is further processed by several other structures of the brain, including the piriform cortex, entorhinal cortex, amygdala, and hippocampus. Any blockage or destruction of the pathway along which smell is transferred and processed may result in anosmia. […] Any problems that cause a disturbance in the pathway that leads to the perception of smell, whether mechanical or along the olfactory neural pathway can lead to anosmia. […] These disorders cause anosmia through inflammation of the mucosa as well as through direct obstruction.

• #1 Anosmia – loss of smell | Better Health Channel

  https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/anosmia-loss-of-smell

  Anosmia means loss of the sense of smell, while hyposmia means reduced smell sensitivity. […] The olfactory neurons are able to recover or regenerate after injury. […] There are numerous medications, diseases, hormonal disturbances and chemicals that can disrupt the sense of smell, sometimes permanently. […] Anosmia means loss of the sense of smell, while hyposmia means reduced smell sensitivity. […] However, different factors that are known to interfere with the smell sense include: […] The nerve cells servicing the olfactory epithelium are unique to the nervous system. Unlike nerve cells anywhere else in the body, the olfactory neurons are able to recover or regenerate after injury. This means that incidences of anosmia can be temporary.

• #1 Loss of Smell – Ear, Nose, and Throat Disorders – Merck Manual Consumer Version

  https://www.merckmanuals.com/home/ear-nose-and-throat-disorders/symptoms-of-nose-and-throat-disorders/loss-of-smell

  Destruction of smell receptors has not yet been confirmed as the mechanism for anosmia. […] Anosmia that is not the result of aging occurs when swelling or another blockage of the nasal passages prevents odors from reaching the olfactory area or when parts of the olfactory area or its connections to the brain are destroyed. […] Damage to the olfactory nerves can also result from infections (such as abscesses) or tumors near the cribriform plate. […] Alzheimer disease and some other degenerative brain disorders (such as multiple sclerosis) can damage the olfactory nerves, commonly causing loss of smell. […] Occasionally, serious infections of the nasal sinuses or radiation therapy for cancer causes a loss of smell or taste that lasts for months or even becomes permanent.

• #1 Smell and Taste Disorders: A Primary Care Approach | AAFP

  https://www.aafp.org/pubs/afp/issues/2000/0115/p427.html/1000

  The causes of olfactory dysfunction that are most amenable to treatment include obstructing polyps or other masses (treated by excision) and inflammation (treated with steroids). […] Age-related deficits in the ability to smell are well documented, and such deficits appear in the majority of elderly patients who are healthy and taking no medications. […] However, the complaint of smell loss should never be attributed just to age, and other causes should be sought. […] Olfactory disturbance has many possible causes. In most instances, loss of smell is caused by nasal and sinus disease, upper respiratory tract infection or head trauma. […] It is important to have a high index of suspicion for subacute sinusitis, because decreased smell (hyposmia) can occur without other nasal or sinus symptoms typically associated with sinusitis.

• #1 Olfactory Loss in Rhinosinusitis: Mechanisms of Loss and Recovery

  https://www.mdpi.com/1422-0067/25/8/4460

  Unfortunately, mechanisms of OD in CRS remain largely unknown, which hampers an adequate management of this invalidating phenomenon. […] The problem of odorant conduction might also be at the level of the OC mucus. […] A study on 30 CRS patients found an altered proteomic profile of the OC mucus in both CRSwNP and CRSsNP patients, showing fewer OBPs and metabolizing enzymes in CRS compared to controls. […] In addition to odorant conduction problems, other studies suggest that inflammation at the level of the sino-nasal mucosa plays a role in the development of OD in CRS. […] A biopsy study from 2000 has shown that the OE of CRS patients is capable of mounting an inflammatory response involving the influx of inflammatory cells such as lymphocytes, macrophages, and eosinophils. […] The presence of these inflammatory cells was, in most cases, linked to a defective olfactory function, as measured by the UPSIT smell test.

• #1 Anosmia – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK482152/

  Head trauma is another common cause of anosmia as trauma to the head can cause damage to the nose or sinuses leading to a mechanical blockage and obstruction. Other ways an injury can cause anosmia is by trauma or destruction to the olfactory axons that are present at the cribriform plate, damage to the olfactory bulb, or direct injury to the olfactory areas of the cerebral cortex. […] Normal aging is associated with decreased sensitivity to smell. As individuals age, they lose the number of cells in the olfactory bulb as well as the olfactory epithelium surface area which is important in sensing smell. […] Anosmia is said to be one of the early symptoms of COVID-19 infection. […] Other causes of anosmia include toxic agents such as tobacco, drugs, and vapors that can cause olfactory dysfunction, post-viral olfactory dysfunction, facial traumas involving nasal or sinus deformity, neoplasms in nasal cavity or brain that prohibits the olfactory signal pathway, and subarachnoid hemorrhages. […] The treatment and management depend on the etiology as anosmia is not a diagnosis but a symptom.

• #1 Anosmia Causes – Monell Chemical Senses Center

  https://monell.org/anosmia-causes/

  Smell is a vulnerable sense and olfactory dysfunctions are common. […] The anatomic location of the olfactory nerve, which carries smell information from the receptors inside the nose to the brain, makes it highly susceptible to physical damage. […] Because scientists still don’t completely understand how the sense of smell works in healthy individuals, it is often difficult to identify exactly what goes wrong when a person loses the ability to smell. […] Diseases of the nose and/or sinuses contribute to most cases of smell loss. […] Although nasal-sinus disease often causes swelling of the membranes lining the nasal cavity, we know that more than physical obstruction contributes to the related smell loss. […] The second most common cause of anosmia is a prior upper respiratory infection (URI), such as a cold.

• #1 Post-viral olfactory loss and parosmia | BMJ Medicine

  https://bmjmedicine.bmj.com/content/2/1/e000382

  The emergence of SARS-CoV-2 has brought olfactory dysfunction to the forefront of public awareness, because up to half of infected individuals could develop olfactory dysfunction. Loss of smell which can be partial or total in itself is debilitating, but the distortion of sense of smell (parosmia) that can occur as a consequence of a viral upper respiratory tract infection (either alongside a reduction in sense of smell or as a solo symptom) can be very distressing for patients. […] While early loss of sense of smell is thought to be due to infection of the supporting cells of the olfactory epithelium, the underlying mechanisms of persistent loss and parosmia remain less clear. Depletion of olfactory sensory neurones, chronic inflammatory infiltrates, and downregulation of receptor expression are thought to contribute.

• #1 Mechanism and treatment of olfactory dysfunction caused by coronavirus disease 2019 | Journal of Translational Medicine | Full Text

  https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-023-04719-x

  Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Since the start of the pandemic, olfactory dysfunction (OD) has been reported as a common symptom of COVID-19. […] However, the pathogenesis of post-COVID-19 OD is still unclear, and there is no specific treatment for its patients. […] Currently, it is widely recognized that COVID-19 causes OD, but the exact pathogenesis is not yet clear. […] The above results suggest that the pathogenesis of OD in COVID-19 patients is somewhat specific. It has been suggested that the mechanism of action may be as follows: SARS-CoV-2 is induced by angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2), which are expressed by non-neuronal cells in the olfactory epithelium (OE); SARS-CoV-2 directly invades the OE and causes damage to olfactory neurons; and SARS-CoV-2 causes a cytokine storm that can cause damage to the nervous system, including olfactory receptors.

• #1 Mechanism and treatment of olfactory dysfunction caused by coronavirus disease 2019 | Journal of Translational Medicine | Full Text

  https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-023-04719-x

  Studies have shown that the entry of SARS-CoV-2 into cells depends upon the expression of both ACE2 and TMPRSS2 in target cells. […] The mechanism of SARS-CoV-2 invasion into the OE is shown in Fig. 1. […] In addition, some studies have found a bypass pathway mediated by the neuropilin-1 receptor (NRP1) for SARS-CoV-2 entry, which can also bind with the virus spike protein and promote viral entry into cells. […] The specific pathways and mechanisms by which SARS-CoV-2 affects the central nervous system are controversial. […] SARS-CoV-2 may also damage the central olfactory system through retrograde neural pathways or blood sources, causing OD. […] The damage of stem cells prevents normal regeneration of the olfactory epithelium, resulting in structural changes in the image of the OB a few weeks after infection.

• #1 Mechanism revealed behind loss of smell with COVID-19 | ScienceDaily

  https://www.sciencedaily.com/releases/2022/02/220202124320.htm

  Researchers have discovered a mechanism that may explain why COVID-19 patients lose their sense of smell. […] Infection with the pandemic virus, SARS-CoV-2, indirectly dials down the action of olfactory receptors (OR), proteins on the surfaces of nerve cells in the nose that detect the molecules associated with odors. […] Experiments showed that the presence of the virus near nerve cells (neurons) in olfactory tissue brought an inrushing of immune cells, microglia and T cells, that sense and counter infection. […] Such cells release proteins called cytokines that changed the genetic activity of olfactory nerve cells, even though the virus cannot infect them. […] Immune signaling persists in a way that reduces the activity of genes needed for the building of olfactory receptors. […] Our findings provide the first mechanistic explanation of smell loss in COVID-19 and how this may underlie long COVID-19 biology.

• #1 How the Coronavirus Steals the Sense of Smell – The New York Times

  https://www.nytimes.com/2022/03/02/health/covid-smell.html

  The infected cells shed virus and die, while immune cells flood the region to fight the virus. The subsequent inflammation wreaks havoc on smell receptors, proteins on the surface of the nerve cells in the nose that detect and transmit information about odors. […] The process alters the sophisticated organization of genes in those neurons, essentially short-circuiting them, the researchers reported. […] Their paper significantly advances the understanding of how cells critical to the sense of smell are affected by the virus, despite the fact that they are not directly infected, said Dr. Sandeep Robert Datta, an associate professor of neurobiology at Harvard Medical School, who was not involved in the study. […] “It’s clear that indirectly, if you affect the support cells in the nose, lots of bad things happen,” Dr. Datta said. “The inflammation in the adjacent cells triggers changes in the sensory neurons that prevent them from working properly.”

• #1 Mechanism and treatment of olfactory dysfunction caused by coronavirus disease 2019 | Journal of Translational Medicine | Full Text

  https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-023-04719-x

  It has been shown that invasion by SARS-CoV-2 may cause vascular damage, which in turn leads to a lack of oxygen and nutrient supply to olfactory cells, triggering OD. […] In summary, SARS-CoV-2 infection may cause vascular damage, resulting in impaired blood transport in the nasal cavity and reduced blood flow to the epithelial cells of the nasal mucosa and olfactory nerve cells, which in turn may affect the normal function of olfaction and result in olfactory impairment. […] Overall, SARS-CoV-2 may cause long-term damage to the olfactory system through both direct invasion of OE cells and induction of an inflammatory response. […] It has been demonstrated that SARS-CoV-2 can affect olfactory function in patients with Long COVID by inducing a chronic inflammatory response that simultaneously destroys OSNs and inhibits their regeneration. […] The chronic inflammatory response caused by SARS-CoV-2 can cause continuous immune attacks on OSNs, and the number of OSNs continues to decrease, resulting in persistent OD.

• #1 Mechanism behind loss of smell with COVID-19 revealed

  https://medicalxpress.com/news/2022-02-mechanism-loss-covid-revealed.html

  Researchers have discovered a mechanism that may explain why COVID-19 patients lose their sense of smell. […] Published online February 2 in the journal Cell, the new study found that infection with the pandemic virus, SARS-CoV-2, indirectly dials down the action of olfactory receptors (OR), proteins on the surfaces of nerve cells in the nose that detect the molecules associated with odors. […] Experiments showed that the presence of the virus near nerve cells (neurons) in olfactory tissue brought an inrushing of immune cells, microglia and T cells, that sense and counter infection. Such cells release proteins called cytokines that changed the genetic activity of olfactory nerve cells, even though the virus cannot infect them, say the study authors. […] „Our findings provide the first mechanistic explanation of smell loss in COVID-19 and how this may underlie long COVID-19 biology,” says co-corresponding author Benjamin tenOever, Ph.D., professor in the Department of Microbiology at NYU Langone Health.

• #1 Anosmia Causes – Monell Chemical Senses Center

  https://monell.org/anosmia-causes/

  The third major cause for anosmia is head trauma. […] Aging, exposure to toxic chemicals and varied problems present at birth due to genetics or developmental causes are other well-established factors that can cause problems with smell. […] There is still relatively little known about congenital anosmia.

• #1 How to Regain Your Sense of Smell & Taste After Head Injury

  https://www.cognitivefxusa.com/blog/how-to-regain-sense-of-smell-after-head-injury

  Olfactory dysfunction after a concussion is not associated with symptom severity, but it is associated with a higher risk of anxiety and longer-term post-concussion symptoms. […] If the cribriform plate (a bone located directly behind the nose) is shattered during a severe brain injury, this could damage or even cut the olfactory nerves and result in loss of sense of smell. […] Luckily, the olfactory nerve is one of the few sensory organs that can regenerate new cells through a process called neurogenesis. […] If NVC dysfunction affects any of the brain areas involved in processing information from the olfactory or gustatory systems, patients may experience changes in smell and taste. […] In concussion and TBI patients, this balance between PNS and SNS can be disrupted. […] This imbalance can have devastating consequences throughout the body, including in the olfactory system.

• #1 Smell and Taste Disorders: A Primary Care Approach | AAFP

  https://www.aafp.org/pubs/afp/issues/2000/0115/p427.html/1000

  Olfactory impairment is estimated to occur in nearly 10 percent of patients with head trauma. […] Post-traumatic smell loss is usually caused by shearing injuries to the olfactory nerve fibers at the level of the cribiform plate, but it can also be caused by direct injury to the olfactory bulbs, olfactory tracts or frontal and temporal lobes. […] Cigarette smoking by itself does not cause complete loss of the sense of smell. […] Patients who quit smoking typically have improved olfactory function and flavor sensation over time. […] Olfactory disorders are more likely to be treated successfully when the patient has a reversible cause of intranasal interference such as nasal polyps, rhinitis, allergies or mechanical blockage. […] Because inflammatory nasal disease results in swelling of the olfactory clefts and the release of inflammatory mediators that likely alter the olfactory mucosa, the use of corticosteroids topically (e.g., aqueous nasal spray) or systemically (e.g., oral prednisone) may be helpful.

• #1 Smell (Olfactory) Disorders—Anosmia, Phantosmia & Others | NIDCD

  https://www.nidcd.nih.gov/health/smell-disorders

  People who have a smell disorder either have a decrease in their ability to smell or changes in the way they perceive odors. […] Smell disorders have many causes, with some more obvious than others. Most people who develop a smell disorder have experienced a recent illness or injury. […] A smell disorder can be an early sign of Parkinsons disease, Alzheimers disease, or multiple sclerosis. It can also be related to other medical conditions, such as obesity, diabetes, hypertension, and malnutrition.

• #1 When the Nose Goes | Northwestern Medicine

  https://www.nm.org/healthbeat/healthy-tips/when-the-nose-goes

  Has a smell ever taken you back to a childhood memory or made you feel a strong emotion? […] A loss or decline in sense of smell is very common many studies suggest its more prevalent than hearing loss and can be life-changing. […] Anosmia is complete loss of the ability to smell. Hyposmia, more common than anosmia, is a decrease in the sense of smell. […] There are certainly some reversible causes of olfactory impairment due to inflammation. Other times, after a bad cold or the flu, people can also develop permanent smell impairment, says Dr. Alvi. The mechanism of this injury is not completely understood right now. […] Loss of smell has been shown to occur in up to 17 percent of people following head trauma incidents. […] Smell impairment is also often a symptom of Parkinsons disease and Alzheimers disease.

• #1 Loss of smell and taste | Science for ME

  https://www.s4me.info/threads/loss-of-smell-and-taste.38741/

  COVID-19-related anosmia is associated with viral persistence and inflammation in human olfactory epithelium and brain infection in hamsters. In four patients who developed persistent loss of smell, the authors detected lasting SARS-CoV-2 presence in the olfactory mucosa, suggesting that the prolonged relapsing anosmia in patients with COVID-19 could be due to persistent viral infection. […] Olfactory dysfunction is a common and early symptom of many neurodegenerative diseases, particularly of Parkinson’s disease and other synucleinopathies, Alzheimer’s disease (AD), and mild cognitive impairment heralding its progression to dementia. The neuropathologic changes of olfactory dysfunction in neurodegenerative diseases may involve the olfactory epithelium, olfactory bulb/tract, primary olfactory cortices, and their secondary targets. Olfactory dysfunction is related to deposition of pathological proteins, -synuclein, hyperphosphorylated tau protein, and neurofilament protein in these areas, featured by neurofibrillary tangles, Lewy bodies and neurites inducing a complex cascade of molecular processes including oxidative damage, neuroinflammation, and cytosolic disruption of cellular processes leading to cell death.

• #1 Parosmia – helping patients with olfactory dysfunction – BDA

  https://www.bda.uk.com/resource/parosmia-helping-patients-with-olfactory-dysfunction.html

  Olfactory dysfunction, which has become one of the clinical features of COVID-19, has been associated with less severe disease manifestation. It is thought that smell loss occurs when the coronavirus infects cells that support neurons in the nose. But there might be other ways in which COVID-19 induces smell loss, such as an increase in blood levels of an inflammation-signalling molecule called interleukin-6 or via other inflammatory processes, such as leaky blood vessels, in the olfactory bulbs. […] Parosmia often follows anosmia and, although the underlying mechanism is unknown, it is thought to be a period of the olfactory nerves recovering. This is usually temporary but how long parosmia lasts varies between people greatly. […] Olfactory neurons have a unique ability to regenerate, but it would appear that aberrant regeneration lies at the root of parosmia. The process for the newly regenerated olfactory neurons reconnecting to the brain is a trial-and-error process. In addition, part of the axonal regenerations can become displaced, leading to a misguided regenerating of axons to abnormal parts of the brain.

• #1 Post-viral olfactory loss and parosmia | BMJ Medicine

  https://bmjmedicine.bmj.com/content/2/1/e000382

  The mechanism that leads to the damage of sustentacular cells after SARS-CoV-2 infection remains unclear. Syncytia formation has been hypothesised as one possible mechanism, based in part on extrapolation of findings of lung tissue in post mortem studies of patients who have died from acute SARS-CoV-2 infection. […] For many years, the most plausible hypothesis for parosmia was thought to be aberrant regeneration of olfactory neurons after the acute viral insult, with so-called miswiring, resulting in resulting in neurons that would normally be associated with foul smells being triggered by inoffensive odour molecules. […] Although this theory was held as plausible for several decades, the vast numbers of patients affected by SARS-CoV-2 associated olfactory dysfunction has refocused attention on the subject.

• #1 Insights into the molecular triggers of parosmia based on gas chromatography olfactometry | Communications Medicine

  https://www.nature.com/articles/s43856-022-00112-9

  Parosmia is a debilitating condition in which familiar smells become distorted and disgusting, with consequences for diet and mental health. […] There is currently little understanding of its pathophysiology, and the prevailing hypothesis for the underlying mechanism is aberrant growth of regenerating olfactory sensory neurons after damage. […] We posit that specific highly odour-active molecules are the cause of the parosmic symptom in most cases and initiate the sense of disgust, suggesting that parosmia is, at least in part, a receptor-level phenomenon. […] Although many mechanisms for parosmia have been proposed, there is very little fundamental understanding of its pathophysiology. […] We demonstrate that there is a common set of molecular triggers causing the perception of distortions and a sense of disgust in coffee, and they also trigger distorted perceptions of other chemically related foods.

• #1 Why your returning sense of smell after COVID may feel strange

  https://www.aljazeera.com/features/2022/6/8/why-your-returning-sense-of-smell-after-covid-may-feel-strange

  The cause behind these changes is thought to be due to the unique regenerating capability of olfactory neurons, whereby new cells sprout and reconnect to the brain in a trial-and-error process. As with any nerve injury and regeneration process, as the neurons mature, they can send random impulses haphazardly to the smell centre of the brain, which means smells do not match up to their subjects. There are more than 400 olfactory receptors which work together to send messages to the brain to identify a smell. If some or part of our olfactory neurons are damaged or are regenerating, the exact combination of messages needed to be sent to the brain to identify a scent is distorted, leading to things that should smell familiar having a very different smell. […] While scientists now have a better understanding of what is going on inside of us to alter our sense of smell after COVID-19, there has until recently been less of an understanding of the external molecules in aromas that trigger some of these rancid smells. Scientists at the University of Reading, UK, have found that certain highly potent odour molecules found in coffee trigger the sense of disgust which is experienced by people who have smell disorders as a result of COVID-19.

• #1 Molecular Mechanism of Parosmia | medRxiv

  https://www.medrxiv.org/content/10.1101/2021.02.05.21251085v1.full-text

  Our data neither support nor refute the mis-wiring hypothesis, but certainly place constraints on it. […] The ephaptic theory summarised by Hawkes suggests that demyelination of the OSNs allow the activation of other, non-stimulated OSNs adjacent to the activated OSN by current flow in the extracellular fluid: a form of short circuiting. […] These hypotheses have to explain four characteristics: that parosmia arises almost uniquely in settings of widespread synchronous neuronal destruction either post infection or post traumatic brain injury, is triggered by one of a number of common odorants, is of novel odour character, and that this character is almost always unpleasant. […] The common molecular structures, low odour thresholds and physiochemical grouping of the molecular triggers of parosmia strongly suggest that this is an olfactory receptor-level phenomenon, although we are unable to identify any specific olfactory receptors responsible from publicly available databases.

• #1

  https://healthmatch.io/blog/study-advances-understanding-of-covid-related-loss-of-taste-and-smell

  Losing your sense of taste or smell with COVID-19 is a frustrating phenomenon that researchers are working to better understand. This loss is temporary for some, and more long-term for others (six months or longer). […] In 2020, a systematic review of 24 studies about smell and taste dysfunction indicated that 40% of people lose their sense of taste (dysgeusia) or smell (anosmia) during a COVID infection. […] A different multicenter study conducted in 2021 found that the number may be as high as 74%. Additionally, impairment seems to be more common in people with mild COVID-19 than in moderate-to-severe cases. […] The data suggests that a particular location near two specific genes, UGT2A1 and UGT2A2 has an influence on why some people infected with COVID will experience loss of smell and taste, while others will not.

• #1 Pathogenesis of Olfactory Disorders in COVID-19

  https://www.mdpi.com/2076-3425/12/4/449

  Since the outbreak of the SARS-CoV-2 pandemic, olfactory disorders have been reported as a frequent symptom of COVID-19; however, its pathogenesis is still debated. […] Several theories have been proposed to explain the pathogenesis of COVID-19-related anosmia, including nasal obstruction and rhinorrhea, oedema of the olfactory cleft mucosa, olfactory epithelial damage either within the olfactory receptor cells or the supporting non-neural cells (either direct or immune-mediated), damage to the olfactory bulb, and impairment of the central olfactory pathways. […] Although the pathogenesis of COVID-19-related anosmia is still not fully elucidated, it appears to be mainly due to sensorineural damage, with infection of the olfactory epithelium support cells via the ACE1 receptor and disruption of the OE caused by immense inflammatory reaction, and possibly with direct olfactory sensory neurons infection mediated by the NRP-1 receptor.

• #1 Why COVID-19 Makes People Lose Their Sense of Smell | Scientific American

  https://www.scientificamerican.com/article/why-covid-19-makes-people-lose-their-sense-of-smell1/

  The first paper from a planned data pull 11 days after the survey was posted show an average loss of close to 80 percent of normal smell function, 69 percent of normal taste function, and 39 percent of normal chemesthetic function from COVID-19. […] It does appear, however, from a few early studies, that the anosmia seen with COVID-19 is present in 30-98 percent of infected people seen in hospitals, far more than occurs with other known respiratory infections. […] These studies indicate that there is something special about the virus that attacks the sense of smell in particular, which may help us understand how the virus works. […] Most scientists agree that SARS-CoV-2, like the earlier known SARS-CoV, uses the angiotensin-converting enzyme 2 (ACE2) receptor to gain entry to cells via binding with spike protein.

• #1 Mechanism Revealed Behind Loss of Smell with COVID-19 – BioSpace

  https://www.biospace.com/mechanism-revealed-behind-loss-of-smell-with-covid-19

  Published online February 2 in the journal Cell, the new study found that infection with the pandemic virus, SARS-CoV-2, indirectly dials down the action of olfactory receptors, proteins on the surfaces of nerve cells in the nose that detect the molecules associated with odors. […] Researchers have discovered a mechanism that may explain why COVID-19 patients lose their sense of smell. […] „Our findings provide the first mechanistic explanation of smell loss in COVID-19 and how this may underlie long COVID-19 biology,” says co-corresponding author Benjamin tenOever, PhD, professor in the Department of Microbiology at NYU Langone Health. […] In the current study, experiments confirmed that SARS-CoV-2 infection, and the immune reaction to it, decreases the ability of DNA chains in chromosomes that influence the formation of olfactory receptor building to be open and active, and to loop around to activate gene expression.

• #1

  https://www1.racgp.org.au/newsgp/clinical/why-do-some-people-infected-with-covid-19-lose-the

  Unlike olfactory neurons, these cells express ACE2, which is known to assist viral entry suggesting a possible mechanism through which the virus causes olfactory dysfunction. […] The research from 23andMe found females were more likely (72%) than males (61%) to report the symptom, as were younger people (mean age of 41 years) and those of European ancestry. […] the new paper provides further clues into the biological mechanisms that underly COVID-19-related anosmia as well as ageusia, the authors caution several study limitations.

• #1 Mechanism behind loss of smell with COVID-19 revealed

  https://medicalxpress.com/news/2022-02-mechanism-loss-covid-revealed.html

  One unique symptom of COVID-19 infection is loss of smell without the stuffy nose seen with other infections like the common cold, researchers say. […] The study results build on the discovery over many years that the process which turns genes on involves complex 3-D relationships, where DNA sections become more or less accessible to the cell’s gene-reading machinery based on key signals, and where some DNA chains loop around to form long-range interactions that enable the stable reading of genes. […] In the current study, experiments confirmed that SARS-CoV-2 infection, and the immune reaction to it, decreases the ability of DNA chains in chromosomes that influence the formation of olfactory receptor building to be open and active, and to loop around to activate gene expression. […] The authors say this suggests that COVID-19 causes longer-lasting disruption in chromosomal regulation of gene expression, representing a form of „nuclear memory” that could prevent the restoration of OR transcription even after SARS-CoV-2 is cleared. […] „The realization that the sense of smell relies on 'fragile’ genomic interactions between chromosomes has important implications,” says tenOever.

• #1 Loss of Smell (Anosmia) > Fact Sheets > Yale Medicine

  https://www.yalemedicine.org/conditions/smell-and-taste-disorders

  Anosmia is the partial or full loss of smell. Anosmia can be a temporary or permanent condition. You can partially or completely lose your sense of smell when the mucus membranes in your nose are irritated or obstructed such as when you have a severe cold or a sinus infection, for example. […] The sense of smell is important to overall health and nutrition since diminished sensations can lead to poor appetite and malnutrition, especially in the elderly. An altered sense of smell may pose other health-related problems. People with anosmia may accidentally consume soured or rancid foods because they are unable to detect odors that signal spoilage. Those with anosmia may also be unaware when they are breathing toxic, polluted or smoke-filled air. […] In addition, the olfactory pathways, which send messages between the nasal passages and the brain, can become impaired from age and from certain medications. Also, certain medical conditions can dull or diminish the sense of smell.

• #1

  https://link.springer.com/article/10.1007/s00441-020-03381-9

  Odours serve as warning signals, e.g., for the detection of gas or hygiene-related domains. […] Those signalling functions of odours are disturbed in anosmia. […] Independent from its cause, patients report similar impairments when it comes to the impact of anosmia on daily life functioning. […] About one third of the patients with acquired olfactory dysfunction report a negative impact of their disorder on a social domain, especially when it comes to romantic relationships. […] Although the majority of patients deal well with olfactory impairment in their daily life, about one third of those individuals with olfactory loss who seek professional help states substantial reduction in overall life quality. […] The poor sensitivity of self-reported olfactory impairment suggests that for the majority of those affected, the individual suffering is not sufficient to seek treatment.

• #1 Azthena logo with the word Azthena

  https://www.news-medical.net/news/20220202/Researchers-discover-mechanism-behind-loss-of-smell-in-people-with-COVID-19.aspx

  If olfactory gene expression ceases every time the immune system responds in certain ways that disrupts inter-chromosomal contacts, then the lost sense of smell may act as the 'canary in the coal mine,’ providing early signals that the COVID-19 virus is damaging brain tissue before other symptoms present, and suggesting new ways to treat it.

• #1 Post-viral olfactory loss and parosmia | BMJ Medicine

  https://bmjmedicine.bmj.com/content/2/1/e000382

  The vast number of patients affected by SARS-CoV-2 olfactory dysfunction has allowed large scale studies to help resolve some of these questions of recovery in this specific cohort. […] The high prevalence of olfactory dysfunction after infection with SARS-CoV-2 has provided an unseen opportunity to study the underlying pathophysiological mechanism of post-viral olfactory loss, with considerable advances in the field, which could yield novel therapeutic options.

• #1

  https://healthmatch.io/blog/study-advances-understanding-of-covid-related-loss-of-taste-and-smell

  The researchers suggest that COVID infection downregulates the sensitive receptors in your nose. Downregulation refers to reducing or suppressing response to stimuli the stimuli, in this case, being a smell or taste. […] The realization that the sense of smell relies on fragile genomic interactions between chromosomes has important implications providing early signals that the COVID-19 virus is damaging brain tissue before other symptoms present, and suggesting new ways to treat it. […] Researchers have identified a specific location on a chromosome that is now associated with a genetic risk factor for loss of smell and taste. These findings stand to advance treatment options and allow doctors to estimate recovery time more accurately.

• #1 Insights into the molecular triggers of parosmia based on gas chromatography olfactometry | Communications Medicine

  https://www.nature.com/articles/s43856-022-00112-9

  Our finding that the sense of distortion is reliably triggered by a common group of low threshold odorants advances our understanding of this debilitating condition and places constraints on the prevailing pathophysiological hypotheses. […] The common molecular structures, low odour thresholds and physiochemical grouping of the molecular triggers of parosmia suggest that this is related to peripheral changes in the olfactory epithelium with downstream consequences. […] This study represents a significant development in the understanding of this increasingly widespread condition and will guide further research and future therapies.

• #1 COVID-related loss of smell tied to changes in the brain | CIDRAP

  https://www.cidrap.umn.edu/covid-19/covid-related-loss-smell-tied-changes-brain

  A new study of 73 adults recovering from COVID-19 finds that those who lost their sense of smell showed behavioral, functional, and structural brain changes. […] On MRI conducted during the game, loss of smell was associated with decreased functional activity during decision-making, loss of white-matter integrity, and thinning of the outer layer of the cerebrum in the parietal regions (responsible for processing sensory input, understanding spatial relationships, and how to navigate). […] „Hence, anosmia could serve as both a potential marker of virus-induced damage to neuronal tissues and a marker for individuals susceptible to brain damage.” […] Research is needed into the extent that loss of smell reflects COVID-related brain damage, whether it is a marker of patient susceptibility to different neuropathologic mechanisms, the mechanism of the link between loss of smell and brain changes, and treatment targets, the researchers concluded.

• #1 Restoring Smell and Taste After Covid

  https://research.jefferson.edu/2023-magazine/restoring-smell-and-taste-after-covid.html

  Many questions remain unanswered about why some people are more susceptible to prolonged smell loss than others, and whether there are lasting changes in the brain. […] The SARS-CoV-2 virus enters the nostril and travels to the olfactory epithelium, where it binds to ACE-2 receptors on the supporting cells around the olfactory sensory neurons (blue), causing inflammation (in red). […] After spraying a numbing agent up the nose, a dissolvable sponge saturated with platelet rich plasma or PRP is inserted using an endoscope. […] PRP is generated from a patients own blood, a sample of which is spun down rapidly in a centrifuge to separate the platelets from other blood cells and concentrate them within the plasma, the clear liquid portion of blood. […] The results of their pilot trial are promising. Among those who completed a three-month course of PRP treatments, 60% experienced improvements. […] These studies will collect more evidence for PRP as a treatment not just for COVID-19-related anosmia, but for other types of smell loss as well.

• #1 Anosmia – Wikipedia

  https://en.wikipedia.org/wiki/Anosmia

  It can be caused by chronic meningitis and neurosyphilis that would increase intracranial pressure over a long period of time, and, in some cases, by ciliopathy, including ciliopathy due to primary ciliary dyskinesia. […] Anosmia may very occasionally be an early sign of a degenerative brain disease such as Parkinson’s disease and Alzheimer’s disease. […] Chemosensory disturbances, including loss of smell or taste, are the predominant neurological symptom of COVID-19. As many as 80% of COVID-19 patients exhibit some change in chemesthesis, including smell. Loss of smell has also been found to be more predictive of COVID-19 than all other symptoms, including fever, cough, or fatigue, based on a survey of 2 million participants in the UK and US. […] Studies have indicated that patients who presented with anosmia during the acute phase of COVID-19 are more likely to develop changes in decision-making, exhibiting more impulsive responses, which are associated with functional and structural brain changes.

• #1 Decreased ability to identify odors can predict death – UChicago Medicine

  https://www.uchicagomedicine.org/forefront/news/2014/october/decreased-ability-to-identify-odors-can-predict-death

  Olfactory dysfunction is a harbinger of mortality. […] The hazards of smell loss were „strikingly robust,” the researchers note, above and beyond most chronic diseases. […] Olfactory dysfunction was better at predicting mortality than a diagnosis of heart failure, cancer or lung disease. […] For those already at high risk, lacking a sense of smell more than doubled the probability of death. […] „We think loss of the sense of smell is like the canary in the coal mine,” said the study’s lead author Jayant M. Pinto, MD, an associate professor of surgery at the University of Chicago who specializes in the genetics and treatment of olfactory and sinus disease. […] „It doesn’t directly cause death, but it’s a harbinger, an early warning that something has gone badly wrong, that damage has been done.”

• #1 Loss of Smell (Anosmia) > Fact Sheets > Yale Medicine

  https://www.yalemedicine.org/conditions/smell-and-taste-disorders

  Your physician will examine you to determine the cause of your smell disturbance. Because anosmia can result from any number of conditions, your doctor will first address the primary condition that seems to be causing the problem. […] However, it’s important to know that sometimes the cause of smell disorder can’t be determined for certain. And sometimes anosmia cannot be treated.

• #1 Potential Cause of COVID-19 Smell Loss Identified | Technology Networks

  https://www.technologynetworks.com/neuroscience/news/potential-cause-of-covid-19-smell-loss-identified-358184

  The realization that the sense of smell relies on fragile genomic interactions between chromosomes has important implications, says Dr. tenOever. If olfactory gene expression ceases every time the immune system responds in certain ways that disrupts inter-chromosomal contacts, then the lost sense of smell may act as the canary in the coal mine, providing early signals that the COVID-19 virus is damaging brain tissue before other symptoms present, and suggesting new ways to treat it.

• #1 Potential Cause of COVID-19 Smell Loss Identified | Technology Networks

  https://www.technologynetworks.com/neuroscience/news/potential-cause-of-covid-19-smell-loss-identified-358184

  Researchers have discovered a mechanism that may explain why people with COVID-19 lose their sense of smell. […] The study results build on the discovery over many years that the process that turns on genes involves complex 3D relationships, where DNA sections become more or less accessible to the cells gene-reading machinery based on key signals, and where some DNA chains loop around to form long-range interactions that enable the stable reading of genes. […] In the current study, experiments confirmed that SARS-CoV-2 infection, and the immune reaction to it, decreases the ability of DNA chains in chromosomes that influence the formation of olfactory receptor building to be open and active, and to loop around to activate gene expression. […] The authors say this suggests that COVID-19 causes longer-lasting disruption in chromosomal regulation of gene expression, representing a form of nuclear memory that could prevent the restoration of olfactory receptor transcription even after SARS-CoV-2 is cleared.

• #1 The Mystery of Smell | Harvard Magazine

  https://www.harvardmagazine.com/2021/10/feature-mystery-of-smell

  If the infected cells were so damaged that the neuron also died, it would take months for the neuron to regrow. […] And in some cases, perhaps the viral destruction in the epithelium, especially to the stem cells, was so complete that the neurons would never be able to regrow, and sense of smell would never return. […] For researchers like him and Murthy, the fresh urgency directed at their field is an unfamiliar feeling, but a galvanizing one. […] Right now, we have no clinically validated treatments for the loss of smell as a result of a virus or trauma, Datta says. […] We just dont know. […] The implications of this virus are huge, Holbrook says. […] There is so much work that still needs to be done.

• #2

  https://link.springer.com/article/10.1007/s00441-020-03381-9

  The sense of smell essentially contributes to social communication, guides nutrition behaviour and elicits avoidance towards environmental hazards. Olfactory smell impairment may hence entail severe consequences for affected individuals. […] About one third of patients seeking professional help reports significant diminished life quality, and as olfactory disorders affect 3% up to 22% in the general population, early detection and treatment strategies are essential to provide. […] Quantitative olfactory dysfunction can either be acquired after birth or congenital. The latter one includes genetic conditions and prenatally acquired diseases with associated olfactory dysfunction. […] Most frequently, olfactory dysfunction is acquired due to sinonasal disease (30%), upper respiratory tract infection (URTI, 25%), traumatic brain injury (TBI, 14%) or unknown (idiopathic, 12%).

• #2 Olfactory Nerve: Overview, Function & Anatomy

  https://my.clevelandclinic.org/health/body/23081-olfactory-nerve

  Issues that affect your olfactory system can cause: […] Anosmia, complete loss of smell. […] Dysosmia (also called phantosmia), unpleasant or strange odors that occur spontaneously. […] Hyposmia, partial loss of smell. […] Parosmia, distorted sense of smell. For example, familiar foods may smell like chemicals or mold. […] Medical conditions and other situations that may affect olfactory nerve function include: […] SARS-CoV-2, the virus that causes coronavirus (COVID-19) disease. […] Up to half of the people with COVID-19 experience loss of smell. Researchers are still exploring why. But its possible that viral infections, like SARS-CoV-2, the virus that causes COVID-19, damage olfactory receptors. Many people regain their sense of smell. But it can take several months. […] Many conditions can affect cranial nerve 1, including COVID-19, diabetes and Alzheimers.

• #2 Physician explains how COVID-19 mutes sense of smell – Scope

  https://scopeblog.stanford.edu/2022/04/15/physician-explains-how-covid-19-mutes-sense-of-smell/

  Some even hypothesize smell loss is a benevolent sacrifice made to protect something even more critical: the central nervous system. […] Olfactory neurons naturally regenerate, but when they do so among glitchy support cells, the neurons don’t receive the nutrients and structural help necessary to grow into healthy cells. […] Olfactory neurons can only do their job after the virus is finally cleared and the supporting cells recover. […] In her paper, she’s published an algorithm that collects information about symptoms, duration of illness and other COVID-19-related details, then spits out guidance for doctors and patients as they navigate care and treatment options, such as olfactory training — in other words, smell rehab. […] Over that time, olfactory nerves regenerate and the support cells can slowly recover, enabling the odor-sensing neurons to process chemicals and transmit smell signals correctly.

• #2 Anosmia – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK482152/

  Anosmia is the inability to perceive smell/odor. It can be temporary or permanent and acquired or congenital. There are many causes. Neurological causes can include disturbances to the sensory nerves that make up the olfactory bulb or anywhere along the path in which the signal of smell is transferred to the brain. From the olfactory bulb, the signal is further processed by several other structures of the brain, including the piriform cortex, entorhinal cortex, amygdala, and hippocampus. Any blockage or destruction of the pathway along which smell is transferred and processed may result in anosmia. […] Any problems that cause a disturbance in the pathway that leads to the perception of smell, whether mechanical or along the olfactory neural pathway can lead to anosmia. […] These disorders cause anosmia through inflammation of the mucosa as well as through direct obstruction.

• #2 Lost or changed sense of smell

  https://www.nhs.uk/conditions/lost-or-changed-sense-smell/

  A change in your sense of smell can be unpleasant and affect how things taste. But it’s not usually serious and may get better in a few weeks or months. […] Changes in sense of smell are most often caused by: illnesses such as a cold, flu or COVID-19, sinusitis (sinus infection), an allergy, like hay fever, growths in your nose (nasal polyps). […] These problems can cause: loss of smell (anosmia), smelling things that are not there (phantosmia), like smoke or burnt toast, reduced sense of smell (hyposmia), changes to how things smell (parosmia). […] Sometimes changes in sense of smell cannot be treated and may be permanent. […] A treatment called smell training can help some people.

• #2 Smell and Taste Disorders: A Primary Care Approach | AAFP

  https://www.aafp.org/pubs/afp/issues/2000/0115/p427.html

  Smell and taste disorders are common in the general population, with loss of smell occurring more frequently. […] While the most common causes of smell disturbance are nasal and sinus disease, upper respiratory infection and head trauma, frequent causes of taste disturbance include oral infections, oral appliances (e.g., dentures), dental procedures and Bell’s palsy. […] The causes of olfactory dysfunction that are most amenable to treatment include obstructing polyps or other masses (treated by excision) and inflammation (treated with steroids). […] Age-related deficits in the ability to smell are well documented, and such deficits appear in the majority of elderly patients who are healthy and taking no medications. […] Olfactory disturbance has many possible causes. In most instances, loss of smell is caused by nasal and sinus disease, upper respiratory tract infection or head trauma.

• #2 Post-Viral Olfactory Loss – Fifth Sense

  https://www.fifthsense.org.uk/post-viral-olfactory-loss/

  Everyone will experience anosmia at some point in their life when afflicted by a cold; we all know that feeling of being bunged up, unable to smell things properly or appreciate food. […] The exact mechanism behind post-viral anosmia isnt yet understood, but it is clear that the various viruses that cause the common cold, including flu, somehow damage and interfere with the olfactory epithelium. This is the layer of mucous membrane at the very top of the nasal cavity which contains the olfactory receptor cells. […] As weve said above, the mechanism by which viruses cause a loss of smell is not yet understood, which makes treatment difficult. […] Studies have shown that spontaneous recovery is more common in patients who have suffered postviral olfactory loss than with any other causation.

• #2 Pathophysiological relationship between COVID-19 and olfactory dysfunction: A systematic review | Brazilian Journal of Otorhinolaryngology

  https://www.elsevier.es/en-revista-brazilian-journal-otorhinolaryngology-english-edition–497-articulo-pathophysiological-relationship-between-covid-19-olfactory-S1808869421000732

  SARS-CoV-2 is the pathogen of COVID-19. […] Olfactory disorder is one of the main manifestations of COVID-19, however, research is still required to clarify the mechanism involved in SARS-CoV-2 induced anosmia. […] Both human cell receptors ACE2 and TMPRSS2 are essential for the SARS-CoV-2 entrance. These receptors are mostly present in the olfactory epithelium cells, therefore, the main hypothesis is that anosmia is caused due to damage to non-neuronal cells which, thereafter, affects the normal olfactory metabolism. […] Damage to non-neuronal cells explains the average recovery lasting a few weeks. This injury can be exacerbated by an aggressive immune response, which leads to damage to neuronal cells and stem cells inducing a persistent anosmia. […] The main mechanism is associated with olfactory epithelium damage, targeting predominantly non-neuronal cells. However, neuronal cells can also be affected, worsening the condition of olfactory loss.

• #2 Mechanism revealed behind loss of smell with COVID-19 | ScienceDaily

  https://www.sciencedaily.com/releases/2022/02/220202124320.htm

  The study results build on the discovery over many years that the process which turns genes on involves complex 3-D relationships, where DNA sections become more or less accessible to the cell’s gene-reading machinery based on key signals. […] Experiments confirmed that SARS-CoV-2 infection, and the immune reaction to it, decreases the ability of DNA chains in chromosomes that influence the formation of olfactory receptor building to be open and active. […] The authors say this suggests that COVID-19 causes longer-lasting disruption in chromosomal regulation of gene expression, representing a form of „nuclear memory” that could prevent the restoration of OR transcription even after SARS-CoV-2 is cleared. […] If olfactory gene expression ceases every time the immune system responds in certain ways that disrupts inter-chromosomal contacts, then the lost sense of smell may act as the „canary in the coalmine,” providing any early signals that the COVID-19 virus is damaging brain tissue before other symptoms present.

• #2 How the Coronavirus Steals the Sense of Smell – The New York Times

  https://www.nytimes.com/2022/03/02/health/covid-smell.html

  The immune response altered the architecture of genes in the neurons, disrupting production of odor receptors, said Marianna Zazhytska, a postdoctoral fellow at the Zuckerman Institute and one of the paper’s first authors, along with a graduate student, Albana Kodra. […] “It is not the virus itself causing all this reorganization — it’s the systemic inflammatory response,” Dr. Zazhytska said. “The nerve cells are not hosting the virus, but they are not doing what they did before.” […] The ability of the olfactory receptors to send and receive messages is disrupted. But the neurons don’t die, and so the system can recover after the illness resolves. […] “We saw early on that upon infection, the genomic organization of these neurons changes completely — they’re unrecognizable compared to how they normally are,” Dr. Lomvardas said. […] “There is a signal released from the infected cells that is received by the neurons that normally detect odors, and tells them to reorganize and stop expression of olfactory receptor genes,” he said.

• #2 How to Regain Your Sense of Smell & Taste After Head Injury

  https://www.cognitivefxusa.com/blog/how-to-regain-sense-of-smell-after-head-injury

  Olfactory dysfunction after a concussion is not associated with symptom severity, but it is associated with a higher risk of anxiety and longer-term post-concussion symptoms. […] If the cribriform plate (a bone located directly behind the nose) is shattered during a severe brain injury, this could damage or even cut the olfactory nerves and result in loss of sense of smell. […] Luckily, the olfactory nerve is one of the few sensory organs that can regenerate new cells through a process called neurogenesis. […] If NVC dysfunction affects any of the brain areas involved in processing information from the olfactory or gustatory systems, patients may experience changes in smell and taste. […] In concussion and TBI patients, this balance between PNS and SNS can be disrupted. […] This imbalance can have devastating consequences throughout the body, including in the olfactory system.

• #2 Anosmia – Wikipedia

  https://en.wikipedia.org/wiki/Anosmia

  It can be caused by chronic meningitis and neurosyphilis that would increase intracranial pressure over a long period of time, and, in some cases, by ciliopathy, including ciliopathy due to primary ciliary dyskinesia. […] Anosmia may very occasionally be an early sign of a degenerative brain disease such as Parkinson’s disease and Alzheimer’s disease. […] Chemosensory disturbances, including loss of smell or taste, are the predominant neurological symptom of COVID-19. As many as 80% of COVID-19 patients exhibit some change in chemesthesis, including smell. Loss of smell has also been found to be more predictive of COVID-19 than all other symptoms, including fever, cough, or fatigue, based on a survey of 2 million participants in the UK and US. […] Studies have indicated that patients who presented with anosmia during the acute phase of COVID-19 are more likely to develop changes in decision-making, exhibiting more impulsive responses, which are associated with functional and structural brain changes.

• #2 You can train your nose – and 4 other surprising facts about your sense of smell

  https://theconversation.com/you-can-train-your-nose-and-4-other-surprising-facts-about-your-sense-of-smell-245366

  Partial or full loss of smell is often an early indicator for a range of neurodegenerative diseases, including Alzheimers and Parkinsons diseases. […] Smell training is emerging as a promising experimental treatment option for olfactory dysfunction. For people experiencing smell loss after COVID, its been show to improve the ability to detect and differentiate odours. […] This training has also been shown to alleviate depressive symptoms and improve cognitive decline both in older adults and those suffering from dementia.

• #2 Insights into the molecular triggers of parosmia based on gas chromatography olfactometry | Communications Medicine

  https://www.nature.com/articles/s43856-022-00112-9

  Our finding that the sense of distortion is reliably triggered by a common group of low threshold odorants advances our understanding of this debilitating condition and places constraints on the prevailing pathophysiological hypotheses. […] The common molecular structures, low odour thresholds and physiochemical grouping of the molecular triggers of parosmia suggest that this is related to peripheral changes in the olfactory epithelium with downstream consequences. […] This study represents a significant development in the understanding of this increasingly widespread condition and will guide further research and future therapies.

• #2 Why your returning sense of smell after COVID may feel strange

  https://www.aljazeera.com/features/2022/6/8/why-your-returning-sense-of-smell-after-covid-may-feel-strange

  The authors theorise the brain miscategorises this scent molecule earlier than others as it has an exceptionally low odour threshold, meaning it can be present in only tiny quantities before its scent is detected by our noses compared with other scent molecules which are picked up later in the smell recovery process. […] As the world continues to learn how to adapt to the coronavirus pandemic, more research is needed to better understand the exact mechanism by which COVID-19 impacts our sense of smell and the routes by which it is best recovered.

• #2 Pathogenesis of Olfactory Disorders in COVID-19

  https://www.mdpi.com/2076-3425/12/4/449

  The pathogenesis of COVID-19 related anosmia is still not fully elucidated; however, it appears to be mainly due to sensorineural damage, with infection of the OE support cells via the ACE1 receptor and disruption of the OE caused by immense inflammatory reaction, and possibly with direct OSNs infection mediated by the NRP-1 receptor. Involvement of the higher olfactory pathways and a conductive component of OD, as well as genetic factors, may also be considered.

• #2 Why COVID-19 Makes People Lose Their Sense of Smell | Scientific American

  https://www.scientificamerican.com/article/why-covid-19-makes-people-lose-their-sense-of-smell1/

  SARS-CoV-2 additionally appears to need TMPRSS2, a protease, to help prime the spike protein in the process of gaining entry to cells and a few other proteins. […] In the nose, expression is seen in both the respiratory epithelium (RE) and the olfactory sensory epithelium (OSE) but in much higher levels in the OSE. […] So far, it appears that olfactory sensory neurons themselves do not have the right expression patterns to bind SARS-CoV-2, which means that the virus may not directly invade these neurons that synapse directly in cortex in the olfactory bulbs. […] There is evidence that the virus can migrate into the central nervous system via the nose and olfactory bulbs as well as by other routes without invading the sensory neurons. […] However, the expression patterns of ACE2 and TMPRSS2 and the sudden onset and relatively fast recovery suggest that COVID-19 anosmia is not caused by damage to the central nervous system but rather by the loss of smell information before it gets to the brain.

• #2 Mechanism Revealed Behind Loss of Smell with COVID-19 – BioSpace

  https://www.biospace.com/mechanism-revealed-behind-loss-of-smell-with-covid-19

  The authors say this suggests that COVID-19 causes longer-lasting disruption in chromosomal regulation of gene expression, representing a form of „nuclear memory” that could prevent the restoration of OR transcription even after SARS-CoV-2 is cleared. […] „The realization that the sense of smell relies on „fragile” genomic interactions between chromosomes has important implications,” says tenOever.

• #2 Olfactory training and COVID-19-related loss of smell | Perio Implant Advisory

  https://www.perioimplantadvisory.com/clinical-tips/article/14198911/olfactory-training-and-covid-19-related-loss-of-smell

  Temporary loss of smell (anosmia), partial loss of smell (hyposmia), and distorted loss of smell (parosmia) are common symptoms of COVID-19 infection. The mechanism behind COVID-19-induced smell loss is thought to be the result of viral invasion of the neural olfactory epithelium. One study suggests that the novel coronavirus changes the sense of smell in patients not by directly infecting these neurons but by affecting the function of supporting cells, called sustentacular cells. Because these cells have large amounts of angiotensin converting enzyme 2 (ACE2) receptors—the portal of entry for SARS-CoV-2—indirect damage to the olfactory nerve and olfactory pathway occurs. Fortunately, the olfactory nerve is the only cranial nerve that has a natural regenerative capacity. […] On average, 50% of patients will recover their sense of smell in the first two to three weeks and another 40% in the first eight weeks postinfection. […] Unfortunately, 10% of patients will continue to have some form of smell loss after eight weeks, and 2%–5% can have permanent anosmia.

• #2

  https://link.springer.com/article/10.1007/s00441-020-03381-9

  A current example of post-viral olfactory loss is olfactory impairment in covid-19 patients. […] Anosmia does not imply that all chemosensory function is lost; most patients are still able to perceive trigeminal sensations. […] The altered perception of food is often an initial sign of olfactory loss which is noticed by the patients themselves. […] Patients with acquired olfactory dysfunction often report altered eating behaviour, as well as anhedonia in relation to food. […] Up to 70% of patients with acquired anosmia report a decreased pleasure of eating or drinking. […] Detection of edible food, rejection of spoiled food regulation of appetite and hedonic experience such as flavour perceptionall those features of nutrition are mediated by chemosensation and hence affected in anosmia.

• #2 Decreased ability to identify odors can predict death – UChicago Medicine

  https://www.uchicagomedicine.org/forefront/news/2014/october/decreased-ability-to-identify-odors-can-predict-death

  Measuring smell with this test, they learned that: […] When the researchers adjusted for demographic variables such as age, gender, socioeconomic status (as measured by education or assets), overall health, and race, those with greater smell loss when first tested were substantially more likely to have died five years later. […] Even mild smell loss was associated with greater risk. […] „This evolutionarily ancient special sense may signal a key mechanism that affects human longevity,” noted McClintock, the David Lee Shillinglaw Distinguished Service Professor of Psychology, who has studied olfactory and pheromonal communication throughout her career. […] Precisely how smell loss contributes to mortality is unclear. […] The olfactory nerve, the only cranial nerve directly exposed to the environment, may serve as a conduit, they suggest, exposing the central nervous system to pollution, airborne toxins, pathogens or particulate matter. […] McClintock noted that the olfactory system also has stem cells which self-regenerate, so „a decrease in the ability to smell may signal a decrease in the body’s ability to rebuild key components that are declining with age and lead to all-cause mortality.”

• #2 Anosmia Causes – Monell Chemical Senses Center

  https://monell.org/anosmia-causes/

  Smell is a vulnerable sense and olfactory dysfunctions are common. […] The anatomic location of the olfactory nerve, which carries smell information from the receptors inside the nose to the brain, makes it highly susceptible to physical damage. […] Because scientists still don’t completely understand how the sense of smell works in healthy individuals, it is often difficult to identify exactly what goes wrong when a person loses the ability to smell. […] Diseases of the nose and/or sinuses contribute to most cases of smell loss. […] Although nasal-sinus disease often causes swelling of the membranes lining the nasal cavity, we know that more than physical obstruction contributes to the related smell loss. […] The second most common cause of anosmia is a prior upper respiratory infection (URI), such as a cold.

• #2 Mechanism revealed behind loss of smell with COVID-19 | ScienceDaily

  https://www.sciencedaily.com/releases/2022/02/220202124320.htm

  Researchers have discovered a mechanism that may explain why COVID-19 patients lose their sense of smell. […] Infection with the pandemic virus, SARS-CoV-2, indirectly dials down the action of olfactory receptors (OR), proteins on the surfaces of nerve cells in the nose that detect the molecules associated with odors. […] Experiments showed that the presence of the virus near nerve cells (neurons) in olfactory tissue brought an inrushing of immune cells, microglia and T cells, that sense and counter infection. […] Such cells release proteins called cytokines that changed the genetic activity of olfactory nerve cells, even though the virus cannot infect them. […] Immune signaling persists in a way that reduces the activity of genes needed for the building of olfactory receptors. […] Our findings provide the first mechanistic explanation of smell loss in COVID-19 and how this may underlie long COVID-19 biology.

• #3 Smell and Taste Disorders: A Primary Care Approach | AAFP

  https://www.aafp.org/pubs/afp/issues/2000/0115/p427.html/1000

  Olfactory impairment is estimated to occur in nearly 10 percent of patients with head trauma. […] Post-traumatic smell loss is usually caused by shearing injuries to the olfactory nerve fibers at the level of the cribiform plate, but it can also be caused by direct injury to the olfactory bulbs, olfactory tracts or frontal and temporal lobes. […] Cigarette smoking by itself does not cause complete loss of the sense of smell. […] Patients who quit smoking typically have improved olfactory function and flavor sensation over time. […] Olfactory disorders are more likely to be treated successfully when the patient has a reversible cause of intranasal interference such as nasal polyps, rhinitis, allergies or mechanical blockage. […] Because inflammatory nasal disease results in swelling of the olfactory clefts and the release of inflammatory mediators that likely alter the olfactory mucosa, the use of corticosteroids topically (e.g., aqueous nasal spray) or systemically (e.g., oral prednisone) may be helpful.

• #3

  https://link.springer.com/article/10.1007/s00441-020-03381-9

  Odours serve as warning signals, e.g., for the detection of gas or hygiene-related domains. […] Those signalling functions of odours are disturbed in anosmia. […] Independent from its cause, patients report similar impairments when it comes to the impact of anosmia on daily life functioning. […] About one third of the patients with acquired olfactory dysfunction report a negative impact of their disorder on a social domain, especially when it comes to romantic relationships. […] Although the majority of patients deal well with olfactory impairment in their daily life, about one third of those individuals with olfactory loss who seek professional help states substantial reduction in overall life quality. […] The poor sensitivity of self-reported olfactory impairment suggests that for the majority of those affected, the individual suffering is not sufficient to seek treatment.

• #4 Smell and Taste Disorders: A Primary Care Approach | AAFP

  https://www.aafp.org/pubs/afp/issues/2000/0115/p427.html/1000

  However, some investigators have suggested that absence of smell function (anosmia) subsequent to an upper respiratory infection may improve over time without specific treatment. […] In general, the olfactory system regenerates poorly after a head injury. […] Most patients who recover smell function subsequent to head trauma do so within 12 weeks of injury.

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