Tong JY, Wong A, Zhu D, Fastenberg JH, Tham T. The prevalence of olfactory and gustatory dysfunction in COVID-19 patients: A systematic review and meta-analysis. Otolaryngol Head Neck Surg. 2020;163(1):3–11.

Article  PubMed  Google Scholar 

Borsetto D, Hopkins C, Philips V, Obholzer R, Tirelli G, Polesel J, et al. Self-reported alteration of sense of smell or taste in patients with COVID-19: a systematic review and meta-analysis on 3563 patients. Rhinology. 2020;58(5):430–6.

CAS  PubMed  Google Scholar 

Hannum ME, Ramirez VA, Lipson SJ, Herriman RD, Toskala AK, Lin C, et al. Objective sensory testing methods reveal a higher prevalence of olfactory loss in COVID-19-positive patients compared to subjective methods: a systematic review and meta-analysis. Chem Senses. 2020;45(9):865–74.

CAS  PubMed  Google Scholar 

Hu S, Zhang S, You Y, Tang J, Chen C, Wang C, et al. Olfactory dysfunction after COVID-19: metanalysis reveals persistence in one-third of patients 6 months after initial infection. J Infect. 2023;86(5):516–9.

Article  PubMed  PubMed Central  Google Scholar 

Whitcroft KL, Altundag A, Balungwe P, Boscolo-Rizzo P, Douglas R, Enecilla MLB, et al. Position paper on olfactory dysfunction: 2023. Rhinology. 2023;61(33):1–108.

Article  CAS  PubMed  Google Scholar 

O’Byrne L, Webster KE, MacKeith S, Philpott C, Hopkins C, Burton MJ. Interventions for the treatment of persistent post-COVID-19 olfactory dysfunction. Cochrane Database Syst Rev. 2022;9(9):13876.

Google Scholar 

Hwang SH, Kim SW, Basurrah MA, Kim DH. The efficacy of olfactory training as a treatment for olfactory disorders caused by coronavirus disease-2019: A systematic review and meta-analysis. Am J Rhinol Allergy. 2023;37(4):495–501.

Article  PubMed  Google Scholar 

Delgado-Lima AH, Bouhaben J, Delgado-Losada ML. The efficacy of olfactory training in improving olfactory function: a meta-analysis. Eur Arch Otorhinolaryngol. 2024;281(10):5267–84.

Article  PubMed  PubMed Central  Google Scholar 

Fornazieri MA, Garcia ECD, Lopes NMD, Miyazawa INI, Silva GDS, Monteiro RDS, et al. Adherence and efficacy of olfactory training as a treatment for persistent olfactory loss. Am J Rhinol Allergy. 2020;34(2):238–48.

Article  PubMed  Google Scholar 

Pekala K, Chandra RK, Turner JH. Efficacy of olfactory training in patients with olfactory loss: a systematic review and meta-analysis. Int Forum Allergy Rhinol. 2016;6(3):299–307.

Article  PubMed  Google Scholar 

Turner JH. Olfactory training: what is the evidence? Int Forum Allergy Rhinol. 2020;10(11):1199–200.

Article  PubMed  PubMed Central  Google Scholar 

Langdon C, Lehrer E, Berenguer J, Laxe S, Alobid I, Quintó L, et al. Olfactory training in post-traumatic smell impairment: mild improvement in threshold performances: results from a randomized controlled trial. J Neurotrauma. 2018;35(22):2641–52.

Article  PubMed  Google Scholar 

Winn PZ, Hlaing T, Tun KM, Lei SL. Effect of any form of steroids in comparison with that of other medications on the duration of olfactory dysfunction in patients with COVID-19: A systematic review of randomized trials and quasi-experimental studies. PLoS ONE. 2023;18(8):e0288285.

Article  CAS  PubMed  PubMed Central  Google Scholar 

Hopkins C, Alanin M, Philpott C, Harries P, Whitcroft K, Qureishi A, et al. Management of new onset loss of sense of smell during the COVID-19 pandemic - BRS Consensus Guidelines. Clin Otolaryngol. 2021;46(1):16–22.

Article  PubMed  Google Scholar 

Kim DH, Kim SW, Kang MJ, Hwang SH. Efficacy of topical steroids for the treatment of olfactory disorders caused by COVID-19: A systematic review and meta-analysis. Clin Otolaryngol. 2022;47(4):509–15.

Article  PubMed  PubMed Central  Google Scholar 

Rochet M, El-Hage W, Richa S, Kazour F, Atanasova B. Depression, olfaction, and quality of life: a mutual relationship. Brain Sci. 2018;8(5):80.

Article  PubMed  PubMed Central  Google Scholar 

Hummel T, Nordin S. Olfactory disorders and their consequences for quality of life. Acta Otolaryngol. 2005;125(2):116–21.

Article  PubMed  Google Scholar 

Hummel T, Sekinger B, Wolf SR, Pauli E, Kobal G. ‘Sniffin’ sticks’: olfactory performance assessed by the combined testing of odor identification, odor discrimination and olfactory threshold. Chem Senses. 1997;22(1):39–52.

Article  CAS  PubMed  Google Scholar 

Doty RL, Shaman P, Dann M. Development of the university of pennsylvania smell identification test: A standardized microencapsulated test of olfactory function. Physiol Behav. 1984;32(3):489–502.

Article  CAS  PubMed  Google Scholar 

Doty RL, Marcus A, Lee WW. Development of the 12-item cross-cultural smell identification test (CC-SIT). Laryngoscope. 1996;106(3 Pt 1):353–6.

Article  CAS  PubMed  Google Scholar 

Cain WS, Gent JF, Goodspeed RB, Leonard G. Evaluation of olfactory dysfunction in the connecticut chemosensory clinical research center. Laryngoscope. 1988;98(1):83–8.

Article  CAS  PubMed  Google Scholar 

Berube S, Demers C, Pek V, Chen A, Bussiere N, Cloutier F, et al. Effects of olfactory training on olfactory dysfunction induced by COVID-19. ORL. 2022;85(2):57–66.

Article  PubMed  Google Scholar 

Pires IDT, Steffens ST, Mocelin AG, Shibukawa DE, Leahy L, Saito FL, et al. Intensive olfactory training in post-covid-19 patients: a multicenter randomized clinical trial. Am J Rhinol Allergy. 2022;36(6):780–7.

Article  PubMed  Google Scholar 

Lechner M, Liu J, Counsell N, Gillespie D, Chandrasekharan D, Ta NH, et al. The COVANOS trial - insight into post-COVID olfactory dysfunction and the role of smell training. Rhinology. 2022;60(3):188–99.

Article  CAS  PubMed  Google Scholar 

Aldundag A, Yilmaz E, Kesimli MC. Modified olfactory training is an effective treatment method for COVID-19 induced parosmia. Laryngoscope. 2022;132(7):1433–8.

Article  CAS  Google Scholar 

Chung TWH, Zhang H, Wong FKC, Sridhar S, Lee TMC, Leung GKK, et al. A pilot study of short-course oral vitamin A and aerosolised diffuser olfactory training for the treatment of smell loss in long COVID. Brain Sci. 2023;13(7):1014.

Article  CAS  PubMed  PubMed Central  Google Scholar 

De Luca P, Camaioni A, Marra P, Salzano G, Carriere G, Ricciardi L, et al. Effect of ultra-micronized palmitoylethanolamide and luteolin on olfaction and memory in patients with long COVID: Results of a longitudinal study. Cells. 2022;11(16):2552.

Article  PubMed  PubMed Central  Google Scholar 

Pendolino AL, Ottaviano G, Nijim J, Scarpa B, De Lucia G, Berro C, et al. A multicenter real-life study to determine the efficacy of corticosteroids and olfactory training in improving persistent COVID-19-related olfactory dysfunction. Laryngoscope Invest Otolaryngol. 2023;8(1):46–54.

Article  Google Scholar 

Bérubé S, Demers C, Bussière N, Cloutier F, Pek V, Chen AEL, et al. Olfactory training impacts olfactory dysfunction induced by COVID-19: A pilot study. Orl-J Oto-Rhino-Laryngol Head Neck Surg. 2023;85(2):57–66.

Google Scholar 

Hosseinpoor M, Kabiri M, Haghi MR, Soltani TG, Rezaei A, Faghfouri A, et al. Intranasal corticosteroid treatment on recovery of long-term olfactory dysfunction due to COVID-19. Laryngoscope. 2022;132(11):2209–16.

Article  CAS  PubMed  Google Scholar 

Hintschich CA, Dietz M, Haehner A, Hummel T. Topical administration of mometasone is not helpful in post-COVID-19 olfactory dysfunction. Life-Basel. 2022;12(10):1483.

Article  CAS  PubMed  PubMed Central  Google Scholar 

Hautefort C, Corre A, Poillon G, Jourdaine C, Housset J, Eliezer M, et al. Local budesonide therapy in the management of persistent hyposmia in suspected non-severe COVID-19 patients: Results of a randomized controlled trial. Int J Infect Dis. 2023;136:70–6.

Article  CAS  PubMed  Google Scholar 

Schmidt F, Azar C, Goektas O. Treatment of Olfactory Disorders After SARS - CoViD 2 Virus Infection. Ent-Ear Nose Throat J. 2023;103(1):48S-53S.