Biology:Smell training

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Short description: Rehabilitation practice


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]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 "Effects of olfactory training: a meta-analysis". Rhinology 55 (1): 17–26. March 2017. doi:10.4193/Rhin16.195. PMID 28040824. 
  2. ↑ Olfactory dysfunction in COVID-19: diagnosis and management. Whitcroft KL, Hummel T. JAMA. 2020;323:2512–2514. [Abstract] [Google Scholar]
  3. ↑ Chabot A, Huntwork M. Turmeric as a Possible Treatment for COVID-19-Induced Anosmia and Ageusia Cureus. ;13(9). PMCID: PMC8502749.
  4. ↑ "Smell disorders in COVID-19 patients: role of olfactory training: A protocol for systematic review and meta-analysis". Medicine 100 (8): e24862. February 2021. doi:10.1097/MD.0000000000024862. PMID 33663108. 
  5. ↑ Holbrook, Eric H.; Coelho, Daniel H. (2020-02-01). "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. https://pubmed.ncbi.nlm.nih.gov/31685237. 
  6. ↑ "Flavor education and training in olfactory dysfunction: a pilot study". European Archives of Oto-Rhino-Laryngology 277 (7): 1987–1994. July 2020. doi:10.1007/s00405-020-05950-8. PMID 32248300. 
  7. ↑ 7.0 7.1 "Effects of olfactory training in patients with olfactory loss". The Laryngoscope 119 (3): 496–9. March 2009. doi:10.1002/lary.20101. PMID 19235739. 
  8. ↑ "Parosmia is Associated with Relevant Olfactory Recovery After Olfactory Training". The Laryngoscope 131 (3): 618–623. March 2021. doi:10.1002/lary.29277. PMID 33210732. 
  9. ↑ 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. 
  10. ↑ "Nosing In on Kids Who Had Covid and Lost Their Sense of Smell" (in en-US). 2021-03-25. https://khn.org/news/article/pediatric-covid-patients-loss-of-smell-scent-training/. 
  11. ↑ Hummel, T.; Whitcroft, K.L.; Andrews, P.; Altundag, A.; Cinghi, C.; Costanzo, R.M.; Damm, M.; Frasnelli, J. et al. (1 March 2017). "Position paper on olfactory dysfunction". Rhinology Journal 54 (26): 1–30. doi:10.4193/Rhino16.248. PMID 29528615. https://www.rhinologyjournal.com/Documents/Supplements/supplement_26.pdf. Retrieved 5 May 2021. 
  12. ↑ 12.0 12.1 Hopkins, Claire; Alanin, Mikkel; Philpott, Carl; Harries, Phil; Whitcroft, Katherine; Qureishi, Ali; Anari, Shahram; Ramakrishnan, Yujay et al. (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. PMID 32854169. 
  13. ↑ Doty, Richard L. (2019). "Treatments for smell and taste disorders: A critical review". Smell and Taste. Handbook of Clinical Neurology. 164. pp. 455–479. doi:10.1016/B978-0-444-63855-7.00025-3. ISBN 9780444638557. 
  14. ↑ Gamble, Maeve. "People Are Trying a Questionable Therapy to Get Back Their Sense of Smell". Slate. https://slate.com/technology/2021/04/does-smell-therapy-for-people-who-had-covid-19-really-work.html. 
  15. ↑ "The Weird World of Olfactory Training" (in en-us). 17 November 2020. https://www.allure.com/story/olfactory-training-smell-loss-covid-19. 
  16. ↑ "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. October 1989. doi:10.1073/pnas.86.20.7976. PMID 2813372. Bibcode: 1989PNAS...86.7976W. 
  17. ↑ Hura, Nanki; Xie, Deborah X.; Choby, Garret W.; Schlosser, Rodney J.; Orlov, Cinthia P.; Seal, Stella M.; Rowan, Nicholas R. (2020-06-25). "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. PMID 32567798. 

Further reading

  • Michael Barbaro (March 23, 2021). "A Food Critic Loses Her Sense of Smell". The Daily (Podcast). The New York Times. Retrieved March 24, 2021. External link in |publisher= (help)
  • Collins C (February 4, 2021). COVID-19 patients and 'smell training' (Video). The Los Angeles Times.



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