OLFACTORY TRAINING

What is olfactory training?

Olfactory training is a non-pharmacological and non-surgical treatment option for people experiencing olfactory (or smell) dysfunction that can occur after an infection, trauma event, or Parkinson’s disease. Typically, patients expose themselves to 4 different odors twice daily for at least 24 weeks. Each odor is sniffed for at least 20-30 seconds without a break. Each odor should ideally represent a different category of smells, including a fruity or sweet smell (ex, lemon), flowery smell (ex, rose), spicy smell (ex, clove), and resinous smell (ex, eucalyptus).² Olfactory training can also be done for up to 12 odors, which may demonstrate better symptom improvement.¹ It is more effective in younger individuals and those with more severe olfactory dysfunction.

How can olfactory training help alleviate certain long COVID symptoms?

It is estimated that up to one-third of COVID patients can have post-infection smell dysfunction.³ The loss of smell is likely due to multiple mechanisms such as inflammation of the nasal epithelium, damage of olfactory neurons and microglial cells, early cell death of olfactory cells, changes in the nasal cilia, and changes in odor transmission. Olfactory training is believed to help rebuild neural connections between the nose and the brain to help relearn and identify different types of smells.²

What evidence supports olfactory training’s use for long COVID?

A case series of 8 patients (five female, three male) with post-COVID smell dysfunction lasting over three months followed a 30-day olfactory training protocol using plant-derived essential oils. Participants had one training session in the morning and one in the evening, each lasting approximately 15 minutes. Each patient was asked to smell ten plant-derived essential oils through deep inhalation and rapid sniffing. The order of smells included peppermint, lavender, lemon, red spruce, frankincense (orange-like smell), Hyssop CT pinocamphone (spice and herbaceous scent), cinnamon, cloves, savory, and eucalyptus. Based on their self-reported olfactory functioning, there was a significant improvement from 3.6 at baseline to 5.6 out of 10.³

Olfactory training is typically done over a longer time span of 12-24 weeks. However, additional studies have looked at using an expanded number of smells for a shorter time span. One study enrolled 80 patients assigned to olfactory training with four or eight smells over four weeks.⁴ Significant improvements were subjectively measured in both groups, and there were no significant differences between groups in identifying smells. This suggests that utilizing four scents for four weeks may be sufficient for olfactory training.

Another study investigated the efficacy of combined visual-olfactory training compared to olfactory training alone in 275 patients with post-COVID olfactory loss.⁵ Visual-olfactory training included digital images of each scent shown to the participants while smelling it. The study also examined differences between patients choosing scents vs. physicians selecting scents. Results showed no clinically meaningful difference in all groups’ smell identification test scores.

What should you be aware of with olfactory training?

Olfactory training is safe and considered a first-line therapy for olfactory dysfunction. However, certain conditions may benefit from surgery rather than olfactory training, so it is important to ask your doctor before starting it. Smoking tobacco products can worsen olfactory functioning and prevent improvement with olfactory training.

References:

1)      Kronenbuerger M, Pilgramm M. Olfactory Training. 2022 Oct 24. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan. PMID: 33620818.

2)      Windsor M. Smell training is brain training, parosmia success – and five other insights from a new UAB clinic. The University of Alabama at Birmingham. March 27, 2023. Accessed November 2, 2023. https://www.uab.edu/reporter/patient-care/advances/item/10005-smell-training-is-brain-training-parosmia-success-and-five-other-insights-from-a-new-uab-clinic#:~:text=Treatments%20—%20starting%20with%20olfactory%20training,training%20can%20boost%20cognitio

3)      Donelli D, Antonelli M, Valussi M. Olfactory training with essential oils for patients with post-COVID-19 smell dysfunction: A case series. Eur J Integr Med. 2023 Jun;60:102253. doi: 10.1016/j.eujim.2023.102253

4)      Pires ÍAT, Steffens ST, Mocelin AG, Shibukawa DE, Leahy L, Saito FL, Amadeu NT, Lopes NMD, Garcia ECD, Albanese ML, De Mari LF, Ferreira IM, Veiga CA, Jebahi Y, Coifman H, Fornazieri MA, Hamerschmidt R. Intensive Olfactory Training in Post-COVID-19 Patients: A Multicenter Randomized Clinical Trial. Am J Rhinol Allergy. 2022 Nov;36(6):780-787. doi: 10.1177/19458924221113124

5)      Khan AM, Piccirillo J, Kallogjeri D, Piccirillo JF. Efficacy of Combined Visual-Olfactory Training With Patient-Preferred Scents as Treatment for Patients With COVID-19 Resultant Olfactory Loss: A Randomized Clinical Trial. JAMA Otolaryngol Head Neck Surg. 2023 Feb 1;149(2):141-149. doi: 10.1001/jamaoto.2022.4112