The Effect of Olfactory Training in Patients With COVID-19 Induced Olfactory Dysfunction

Aim: The aim is to investigate the effect of olfactory training with essential oils versus olfactory training with placebo-oils in patients with COVID-19 induced olfactory dysfunction

Study design: The study is a placebo-controlled randomized clinical trial with an intervention group and a control group. The intervention group receive four essential oils with scents of orange, lavender, clove, and peppermint. Patients in the control group receive a fragrance kit, consisting of the same containers, but with fragrance-free oils added. Both groups are instructed to smell each of the four oils for 30 seconds in the morning and evening, over a three-month intervention period. Patients are given a diary in which to record their olfactory training. The nurse or medical student instructing the patients in the training and performing the smell and taste tests is blinded.

Study population: Patients referred to the Unit for Sense of Taste and Smell in the Department of Otorhinolaryngology Head & Neck and Audiology at Rigshospitalet.

Inclusion criteria:

* Impaired sense of taste and smell following COVID-19 > 3 months * Hyposmia (16.25-30.5) or anosmia (<16) assessed by Sniffin' Sticks Olfactory Test for Threshold, Discrimination and Identification (TDI) performed in the Unit for Sense of Taste and Smell with or without parosmia based on medical history * > 18 years of age

Exclusion criteria:

* Cause of hyposmia, anosmia or parosmia other than COVID-19 * Does not read or speak Danish * Lack of compliance to perform daily olfactory training

Procedures:

- TDI-test: To assess patients' sense of smell, the TDI-test with Sniffin' Sticks is used, which is a validated tool with normative data.

Questionnaires:

- 'Taste and Smell Tool for Evaluation' is used to investigate quality of life related to impaired sense of taste and smell.