Smell training

Last updated October 22, 2023

Smell training or olfactory training is the act of regularly sniffing or exposing oneself to robust aromas^[1] with the intention of regaining a sense of smell. The stimulating smells used are often selected from major smell categories, such as aromatic, flowery, fruity, and resinous.^[1] Using strong scents, the patient is asked to sniff each different smell for a minimum of 20 seconds, no less than two times per day, for three to six months or more.^[2]^[3] It is used as a rehabilitative therapy to help people who have anosmia or post-viral olfactory dysfunction, a symptom of COVID-19.^[4] It was considered a promising experimental treatment in a 2017 meta-analysis.^[1]

Efficacy

Along with olfactory implants,^[5] smell training is a promising but experimental treatment option.^[1]

Several individual studies have indicated that smell training can increase olfactory sensitivity.^[6]^[7]^[8] In 2021 a meta-analysis was published that examined research studies of olfactory training for treating loss of smell as a consequence of a viral infection. It found clinically significant improvements and supported its use as a treatment option.^[9] As of March 2021, there have been no studies of smell training's efficacy for children.^[10]

In 2017, the International and European Rhinologic Societies recommended smell training for treating loss of smell due to various conditions.^[11] In 2020, the British Rhinological Society published consensus guidelines for the treatment of smell loss due to COVID-19.^[12] Although no specific studies were available at that time, the expert panel made recommendations regarding treatment options and concluded that "olfactory training was recommended for all [COVID-19] patients with persistent loss of sense of smell of more than 2 weeks duration."^[12]

Critics such as Richard Doty have pointed to the small sample sizes in the studies and the potential for the observed improvements to have been the result of nerve regeneration that would have occurred without intervention as reason to be skeptical.^[13]^[14]

Mechanism

Smell training likely achieves results because the olfactory nerve and olfactory bulb have neural plasticity and are able to regenerate.^[1]

History

The idea was first written about by Thomas Hummel, a German psychologist at the Dresden University of Technology, in his 2009 paper "Effects of olfactory training in patients with olfactory loss".^[15] In his original study, Hummel instructed patients with olfactory dysfunction to follow a twice-a-day routine for twelve weeks. The routine included inhaling the odor of rose, lemon, clove, and eucalyptus (phenyl ethyl alcohol, citronellal, eugenol, and eucalyptol respectively) essential oils for ten seconds each. These intense odors each correspond to a different odor category in Henning's odor prism.^[7]

Hummel's paper built on a 1989 study by the Monell Chemical Senses Center in Philadelphia. The study showed that after repeated exposure to androstenone, a chemical which half of all humans cannot detect, some subjects gained the ability to smell it.^[16]

Alternatives

In addition to smell training, other treatments for anosmia that have been researched include systemic steroidal and non-steroidal oral medications, topical medications, and acupuncture.^[17]

Related Research Articles

<span class="mw-page-title-main">Anosmia</span> Inability to smell

Anosmia, also known as smell blindness, is the loss of the ability to detect one or more smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells.

The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell.

Dysgeusia, also known as parageusia, is a distortion of the sense of taste. Dysgeusia is also often associated with ageusia, which is the complete lack of taste, and hypogeusia, which is a decrease in taste sensitivity. An alteration in taste or smell may be a secondary process in various disease states, or it may be the primary symptom. The distortion in the sense of taste is the only symptom, and diagnosis is usually complicated since the sense of taste is tied together with other sensory systems. Common causes of dysgeusia include chemotherapy, asthma treatment with albuterol, and zinc deficiency. Liver disease, hypothyroidism, and rarely certain types of seizures can also lead to dysgeusia. Different drugs could also be responsible for altering taste and resulting in dysgeusia. Due to the variety of causes of dysgeusia, there are many possible treatments that are effective in alleviating or terminating the symptoms of dysgeusia. These include artificial saliva, pilocarpine, zinc supplementation, alterations in drug therapy, and alpha lipoic acid.

The olfactory system, or sense of smell, is the sensory system used for smelling (olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli.

<span class="mw-page-title-main">Androstenone</span> Chemical compound

Androstenone (5α-androst-16-en-3-one) is a 16-androstene class steroidal pheromone. It is found in boar's saliva, celery cytoplasm, and truffle fungus. Androstenone was the first mammalian pheromone to be identified. It is found in high concentrations in the saliva of male pigs, and, when inhaled by a female pig that is in heat, results in the female assuming the mating stance. Androstenone is the active ingredient in 'Boarmate', a commercial product made by DuPont sold to pig farmers to test sows for timing of artificial insemination.

Ageusia is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami. It is sometimes confused with anosmia – a loss of the sense of smell. Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami, most of what is perceived as the sense of taste is actually derived from smell. True ageusia is relatively rare compared to hypogeusia – a partial loss of taste – and dysgeusia – a distortion or alteration of taste.

Parosmia is a dysfunctional smell detection characterized by the inability of the brain to correctly identify an odor's "natural" smell. Instead, the natural odor is usually transformed into an unpleasant aroma, typically a "burned", "rotting", "fecal", or "chemical" smell. There can also be rare instances of a pleasant odor called euosmia. The condition was rare and little-researched until it became relatively more widespread since 2020 as a side effect of COVID-19.

Phantosmia, also called an olfactory hallucination or a phantom odor, is smelling an odor that is not actually there. This is intrinsically suspicious as the formal evaluation and detection of relatively low levels of odour particles is itself a very tricky task in air epistemology. It can occur in one nostril or both. Unpleasant phantosmia, cacosmia, is more common and is often described as smelling something that is burned, foul, spoiled, or rotten. Experiencing occasional phantom smells is normal and usually goes away on its own in time. When hallucinations of this type do not seem to go away or when they keep coming back, it can be very upsetting and can disrupt an individual's quality of life.

Hyposmia, or microsmia, is a reduced ability to smell and to detect odors. A related condition is anosmia, in which no odors can be detected. Some of the causes of olfaction problems are allergies, nasal polyps, viral infections and head trauma. In 2012 an estimated 9.8 million people aged 40 and older in the United States had hyposmia and an additional 3.4 million had anosmia/severe hyposmia.

Dysosmia is a disorder described as any qualitative alteration or distortion of the perception of smell. Qualitative alterations differ from quantitative alterations, which include anosmia and hyposmia. Dysosmia can be classified as either parosmia or phantosmia. Parosmia is a distortion in the perception of an odorant. Odorants smell different from what one remembers. Phantosmia is the perception of an odor when no odorant is present. The cause of dysosmia still remains a theory. It is typically considered a neurological disorder and clinical associations with the disorder have been made. Most cases are described as idiopathic and the main antecedents related to parosmia are URTIs, head trauma, and nasal and paranasal sinus disease. Dysosmia tends to go away on its own but there are options for treatment for patients that want immediate relief.

An odor or odour is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and many animals can perceive via their sense of smell. An odor is also called a "smell" or a "scent", which can refer to either a pleasant or an unpleasant odor.

The sense of smell, or olfaction, is the special sense through which smells are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.

Olfactory memory refers to the recollection of odors. Studies have found various characteristics of common memories of odor memory including persistence and high resistance to interference. Explicit memory is typically the form focused on in the studies of olfactory memory, though implicit forms of memory certainly supply distinct contributions to the understanding of odors and memories of them. Research has demonstrated that the changes to the olfactory bulb and main olfactory system following birth are extremely important and influential for maternal behavior. Mammalian olfactory cues play an important role in the coordination of the mother infant bond, and the following normal development of the offspring. Maternal breast odors are individually distinctive, and provide a basis for recognition of the mother by her offspring.

Many types of sense loss occur due to a dysfunctional sensation process, whether it be ineffective receptors, nerve damage, or cerebral impairment. Unlike agnosia, these impairments are due to damages prior to the perception process.

The University of Pennsylvania Smell Identification Test (UPSIT) is a test that is commercially available for smell identification to test the function of an individual's olfactory system.

Anosmia Awareness Day is a day to spread awareness about anosmia (an-OHZ-me-uh), the loss of the sense of smell. It takes place each year on February 27.

The symptoms of COVID-19 are variable depending on the type of variant contracted, ranging from mild symptoms to a potentially fatal illness. Common symptoms include coughing, fever, loss of smell (anosmia) and taste (ageusia), with less common ones including headaches, nasal congestion and runny nose, muscle pain, sore throat, diarrhea, eye irritation, and toes swelling or turning purple, and in moderate to severe cases, breathing difficulties. People with the COVID-19 infection may have different symptoms, and their symptoms may change over time. Three common clusters of symptoms have been identified: one respiratory symptom cluster with cough, sputum, shortness of breath, and fever; a musculoskeletal symptom cluster with muscle and joint pain, headache, and fatigue; and a cluster of digestive symptoms with abdominal pain, vomiting, and diarrhea. In people without prior ear, nose, or throat disorders, loss of taste combined with loss of smell is associated with COVID-19 and is reported in as many as 88% of symptomatic cases.

Claire Hopkins is a British Ear, Nose & Throat (ENT) surgeon at Guy's Hospital and Professor of Rhinology at King's College London. She is the President of the British Rhinological Society. During the COVID-19 pandemic, Hopkins successfully campaigned to have anosmia recognised as a symptom of COVID-19 in the United Kingdom.

There is increasing evidence suggesting that COVID-19 causes both acute and chronic neurologicalor psychological symptoms. Caregivers of COVID-19 patients also show a higher than average prevalence of mental health concerns. These symptoms result from multiple different factors.

Olfactic communication is a channel of nonverbal communication referring to the various ways people and animals communicate and engage in social interaction through their sense of smell. Our human olfactory sense is one of the most phylogenetically primitive and emotionally intimate of the five senses; the sensation of smell is thought to be the most matured and developed human sense.

References

1 2 3 4 5 Sorokowska A, Drechsler E, Karwowski M, Hummel T (March 2017). "Effects of olfactory training: a meta-analysis". Rhinology. 55 (1): 17–26. doi: 10.4193/Rhin16.195 . PMID 28040824.
↑ Olfactory dysfunction in COVID-19: diagnosis and management. Whitcroft KL, Hummel T. JAMA. 2020;323:2512–2514. [Abstract] [Google Scholar]
↑ Chabot A, Huntwork M. Turmeric as a Possible Treatment for COVID-19-Induced Anosmia and Ageusia Cureus. ;13(9). PMCID: PMC8502749.
↑ Zhang Y, Mei T, Chen Y, Wang L, Jiang L, Liu K, et al. (February 2021). "Smell disorders in COVID-19 patients: role of olfactory training: A protocol for systematic review and meta-analysis". Medicine. 100 (8): e24862. doi:10.1097/MD.0000000000024862. PMC 7909207 . PMID 33663108.
↑ Holbrook, Eric H.; Coelho, Daniel H. (1 February 2020). "Cranial Nerve Stimulation for Olfaction (Cranial Nerve 1)". Otolaryngologic Clinics of North America. 53 (1): 73–85. doi:10.1016/j.otc.2019.09.014. ISSN 1557-8259. PMID 31685237. S2CID 207904053.
↑ Besser G, Oswald MM, Liu DT, Renner B, Mueller CA (July 2020). "Flavor education and training in olfactory dysfunction: a pilot study". European Archives of Oto-Rhino-Laryngology. 277 (7): 1987–1994. doi:10.1007/s00405-020-05950-8. PMC 7286942 . PMID 32248300.
1 2 Hummel T, Rissom K, Reden J, Hähner A, Weidenbecher M, Hüttenbrink KB (March 2009). "Effects of olfactory training in patients with olfactory loss". The Laryngoscope. 119 (3): 496–9. doi:10.1002/lary.20101. PMID 19235739. S2CID 5239574.
↑ Liu DT, Sabha M, Damm M, Philpott C, Oleszkiewicz A, Hähner A, Hummel T (March 2021). "Parosmia is Associated with Relevant Olfactory Recovery After Olfactory Training". The Laryngoscope. 131 (3): 618–623. doi: 10.1002/lary.29277 . PMID 33210732.
↑ Kattar, Nrusheel; Do, Triet M.; Unis, Graham D.; Migneron, Matthew R.; Thomas, Andrew J.; McCoul, Edward D. (February 2021). "Olfactory Training for Postviral Olfactory Dysfunction: Systematic Review and Meta-analysis". Otolaryngology–Head and Neck Surgery. 164 (2): 244–254. doi: 10.1177/0194599820943550 . PMID 32660334. S2CID 220519030.
↑ Rodriguez CH (25 March 2021). "Nosing In on Kids Who Had Covid and Lost Their Sense of Smell". Kaiser Health News. Retrieved 25 March 2021.
↑ Hummel, T.; Whitcroft, K.L.; Andrews, P.; Altundag, A.; Cinghi, C.; Costanzo, R.M.; Damm, M.; Frasnelli, J.; Gudziol, H.; Gupta, N.; Haehne, A.; Holbrook, E.; Hong, S.C.; Hornung, D.; Huttenbrink, K.B.; Kamel, R.; Kobayashi, M.; Konstantinidis, I.; Landis, B.N.; Leopold, D.A.; Macchi, A.; Miwa, T.; Moesges, R.; Mullol, J.; Mueller, C.A.; Ottaviano, G.; Passali, G.C.; Philpott, C.; Pinto, J.M.; Ramakrishnan, V.J.; Rombaux, P.; Roth, Y.; Schlosser, R.A.; Shu, B.; Soler, G.; Stjarne, P.; Stuck, B.A.; Vodicka, J.; Welge-Luessen, A. (1 March 2017). "Position paper on olfactory dysfunction" (PDF). Rhinology Journal. 54 (26): 1–30. doi: 10.4193/Rhino16.248 . PMID 29528615 . Retrieved 5 May 2021.
1 2 Hopkins, Claire; Alanin, Mikkel; Philpott, Carl; Harries, Phil; Whitcroft, Katherine; Qureishi, Ali; Anari, Shahram; Ramakrishnan, Yujay; Sama, Anshul; Davies, Elgan; Stew, Ben; Gane, Simon; Carrie, Sean; Hathorn, Iain; Bhalla, Raj; Kelly, Chrissi; Hill, Nina; Boak, Duncan; Nirmal Kumar, B. (January 2021). "Management of new onset loss of sense of smell during the COVID‐19 pandemic ‐ BRS Consensus Guidelines". Clinical Otolaryngology. 46 (1): 16–22. doi:10.1111/coa.13636. PMC 7461026 . PMID 32854169.
↑ Doty, Richard L. (2019). "Treatments for smell and taste disorders: A critical review". Smell and Taste. Handbook of Clinical Neurology. Vol. 164. pp. 455–479. doi:10.1016/B978-0-444-63855-7.00025-3. ISBN 9780444638557. PMID 31604562. S2CID 204330823.
↑ Gamble, Maeve. "People Are Trying a Questionable Therapy to Get Back Their Sense of Smell". Slate. Retrieved 5 May 2021.
↑ Shapouri B (17 November 2020). "The Weird World of Olfactory Training". Allure. Retrieved 30 March 2021.
↑ Wysocki CJ, Dorries KM, Beauchamp GK (October 1989). "Ability to perceive androstenone can be acquired by ostensibly anosmic people". Proceedings of the National Academy of Sciences of the United States of America. 86 (20): 7976–8. Bibcode:1989PNAS...86.7976W. doi: 10.1073/pnas.86.20.7976 . PMC 298195 . PMID 2813372.
↑ Hura, Nanki; Xie, Deborah X.; Choby, Garret W.; Schlosser, Rodney J.; Orlov, Cinthia P.; Seal, Stella M.; Rowan, Nicholas R. (25 June 2020). "Treatment of post‐viral olfactory dysfunction: an evidence‐based review with recommendations". International Forum of Allergy & Rhinology. 10 (9): 1065–1086. doi:10.1002/alr.22624. ISSN 2042-6976. PMC 7361320 . PMID 32567798.