Review of Best Practice Guidelines on Aromatherapy for Olfactory Restoration: COVID-19 and Others

Abstract

Objective:

The main objective of this study is to establish a training to restore the olfactory sensation after infection with SARS-CoV-2 virus and the sequel to the disease COVID-19, through the inhalation of a sequence of essential oils (EO), systematically. The secondary objective of this study aims at gathering in an organized way the publications on EO that have in the keywords, short running title, or objective the mucosa anti-inflammatory action, respiratory health action, immunological health action, mental and emotional health action, as well as EO that hinder the viral replication. The EO are lipophilic substances extracted from plant species; they are mainly constituted by terpenic structures that are therapeutic bioactives.

Design:

This best practice guide has made a brief compilation of previously published data into an easy-to-understand didactic table.

Interventions:

Based on the research compiled in the table, a sequence of EO for use by inhalation was organized.

Results:

According to the researchers mentioned in the review, the inhalation of EO resensitizes the neural pathways that allow the identification of aroma and flavor. Thus, when this pathway is damaged, the inhalation of EO can help to restore it in a few months, which the average time is 3 months, and can extend up to 8 months.

Conclusions:

Currently, the greatest demand for the restoration olfactory is due to the sequelae of disease COVID-19. However, EO can be used for a loss or decrease in smell or taste caused by other factors, such as psychotropic medications, chronic rhinitis and sinusitis, neurological pathologies, cancer treatments, postinfectious and posttraumatic olfactory loss, older people, and other causes.

Introduction

The nasal cavity has two types of epithelium: the respiratory epithelium and the olfactory epithelium. The respiratory epithelium is located in the majority of the nasal cavity, mainly in the anterior and median area. The olfactory epithelium is located in the upper-posterior area, occupying about 2 cm². ¹ The olfactory neural route starts in the olfactory epithelium, which is covered by the mucus where the olfactory receptor cells are.

The odorant receptors are located at the end of these olfactory receptor cells. There are different olfactory receptors, each of them specific to one type of odorant molecule. When the odorant molecule connects with the olfactory receptor via electrochemical stimulus, the neural route continues through the olfactory bulb, where the glomerulus is found. The signal follows to the mitral cells and goes directly into the central nervous system, more precisely where the limbic system is.

From this point on, with the emotional and physiological stimulus, we can be aware of the smell. This finding was so important that it earned Linda Buck and Richard Alex the 2004 Nobel Prize for Medicine in the field of Physiology^2,3 (Fig. 1).

FIG. 1.

Researcher laureates and the human olfactory neural route. ⁴

The mapping of human olfactory receptors is under extensive research, and many of which have been shown in publications. Recently, olfactory receptors in the cells of the tongue have been discovered, which is in line with reports of a loss of taste along with a loss of smell. This guideline applies the training of olfactory receptors in the cells of the tongue too.^5–7 The COVID-19 virus initially causes an inflammation of the olfactory epithelium, blocking the attachment of the odorant molecule to the olfactory receptor.

A kind of destructuring of some functions of the olfactory epithelium then begins. ⁸ The virus goes through the previously mentioned route: olfactory neuron, olfactory bulb, glomerulus, mitral, and central nervous system into the limbic system. The loss or reduction of smell causes a deep emotional disharmony, as it is one of the primary and essential senses of the animal species. Anxiety, insecurity, and fear are some of the emotional symptoms results from this loss.^9–11 Researchers have shown that the sense of smell can be recovered through training, because there is a cerebral neuroplasticity of this olfactory function, which re-establishes the identification, discrimination, and threshold of smell.^12–14

Essential oils (EO) are lipophilic substances extracted from plants species; they are mainly constituted by terpenic structures that are therapeutic bioactives.^15–24 There is robust research about action therapeutics of EO, in vitro, in vivo pre-clinical in animals and in vivo clinical humans. ²⁵ The SARS-CoV-2 virus infects the body, causing the disease COVID-19. COVID-19 affects health, according to the degree to which it has advanced in the body. ⁸

Based on references review research, according to the activity of EO, the proposition of the current work is to establish an order of EO to be inhaled. Inhaling EO stimulates neural pathways since the olfactory epithelium until the limbic system, ² regardless of which EO is chosen. Inhalation of the EO allows its components to reach the organism as a whole, after the pulmonary exchange in the alveoli. ²⁶ This present research shows an olfactory training guide that adds to the olfactory reestablishment, also the improvement of health in an integral way in the areas of mental, immunological, and respiratory health systems.

Methodology

This best practice guidelines aims at carrying out a brief references review, between 1994 and 2022 years, of research on EO with mucosa anti-inflammatory action, respiratory health action, immunological health action, mental and emotional health action, as well as hindering the viral replication. Following this, the methodological systematization was organized to sensitize the neural route that allows the identification of aroma and flavor, through the inhalation sequence of specific EO separately, as well as the technical sheet to write the observation of smell and taste after each week of EO inhalation. This is a review study, therefore no IRB approval statement was required.

The search terms were “essential oil and anti-inflammatory activity,” “aromatherapy and anti-inflammatory activity,” “essential oil and antivirus activity,” “aromatherapy and antivirus activity,” “essential oil and COVID-19,” “essential oil and SARS-CoV-2,” “aromatherapy and COVID-19,” “aromatherapy and SARS-CoV-2,” “essential oil and immunological health,” “aromatherapy and immunological health,” “essential oil and emotional health,” “aromatherapy and emotional health,” “essential oil and mental health,” “aromatherapy and mental health,” “essential oil and respiratory health,” “essential oil and pulmonary action,” “aromatherapy and respiratory health,” “aromatherapy and pulmonary activity.”

The search was performed in PUBMED and ScienceDirect databases, and other. Inclusion criteria were EO possible to get in commercial brands, and two or more therapeutic activities described for the same EO. Exclusion criteria were fatty oils and duplicate studies. After applying the inclusion and exclusion criteria, 93 publications were included in Table 1.

Table 1.

Review of Essential Oils with Activities Anti-Inflammatory, Antiviral, Respiratory Health, Immunological Health, and Mental/Emotional Health

EO					Activity
Popular name	Botanical name	EO from part used (major components a )	Anti-inflammatory	Antiviral	Respiratory health	Immunological health	Mental and emotional health
Alojan or Ajowan or Ajwain	Trachyspermum ammi	Seeds (thymol, carvacrol, γ-terpinene, para-cymene, β-pinene, α-pinene, camphene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27	HSV-1, PI-328 HIV 29 Parainfluenza type 3 virus 30	Rinite, rinofaringite, amidalite, bronquite 29 Thymol antitussive activities 31	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Anethum or Endro or Dill	Anethum graveolens	Branches/bough with leaves, seeds (limonene e carvone)	Inhibitor of leukotriene production 32	HSV-1, PI-328Influenza type A (H1N1) 31	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Anticonvulsivant 17
Basil	Ocimum basilicum	Leaves (chemotypes: eugenol, thymol, carvacrol, estragole or methyl-chavicol)(chemotype linalool)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27	HSV-118,23,28,31COVID-1929Parainfluenza type 3 virus 30	Antiasthmatic activity 32 Antitussive activities 31
Bay Pepper or Bay Rum	Pimenta racemosa	Leaves and branches/bough (eugenol, chavicol, myrcene, linalool)	Bacterial anti-inflammatory (Bacillus cereus, and others)29,27Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33	HSV-118,23,29PI-329		Immunomodulation 34	Analgesia, anxiolytic 17
Bergamot	Citrus bergamia	Fruit peel or pericarp (linalool, linalyl acetate, limonene)	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33 Reduce cytokines and chemokines 35 Inhibitor of leukotriene production 32	Type A H1N1 (influenza virus)30,31,36	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Improve immune function CD4/CD8 T cell values and NK cell activity37,38	CNS depression, antidepressant, calming, relaxing, sedative 16 Analgesia, anxiolytic 17 CNS synaptic plasticity, brain ischemia and pain 39 Improves the depressive state 38
Bitter orange	Citrus aurantium	Fruit peel or pericarp (limonene, α-pinene, β-pinene, sabinene, myrcene, linalool)	Inhibitor of leukotriene production 32	HSV-1, PI-328	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Improve immune function CD4/CD8 T cell values and NK cell activity37,38	Anticonvulsant and sedative 16 Anxiolytic16,17,40,41Analgesia 17 Improves the depressive state 38 Relaxing 42
Black cumin	Nigella sativa	Seeds (thymoquinone, carvacrol, trans-anethol, terpin-4-eol)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Anti-inflammatory regulation of Th1 and Th2 balance 19 Immunoglobulin E and Th232Blocking of TNF-α transcription and production and by the suppression of the NF-κB activation pathway 43	HSV-118COVID-1923,44	Asthma19,32,45Bronchitis 32 Allergic response in the lung bronchial 45	Immune stimulatory effect 43	Sedative and anxiolytic effect 35 Anticonvulsivante and neuroprotective 46
Black Pepper	Piper nigrum	Fruits (β-caryophyllene, α-humulene, bisabolene, β-elemene, α-pinene, β-pinene, terpinen-4-ol, α-terpineol)	Inhibited the development of edema 47	HSV-118,28PI-328	Respiratory tract (catarrh and colds) 26	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Blue chamomile or German chamomile	Matricaria chamomilla (synonyms: Chamomilla recutita, Matricaria recutita)	Flowers and branches (α-bisabolol and oxides azulene, chamazulene and acetates)	PGE2 and NO path and anti-allergic activity dermatologic 48 Anti-inflammatory components actions 49	HSV-1 and HSV-223,31COVID-1949		Anticonvulsant 16 Stimulatory GABAergic 17 Stress and depression 48 Decreases stress and anxiety 50	Improves the immune system 50
Cajeput	Melaleuca cajuputi	Leaves and flowers (1,8 cineol, α-terpineol, α-pinene, β-caryophyllene)	Reduction of TNF-α and NO production 43	HSV-118	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Ceylon cinnamon	Cinnamomun zeylanicum (synonym: Cinnamomum verum)	Leaves (eugenol, eugenol acetate, caryophyllene) and bark (cinnamaldehyde, caryophyllene, eugenol)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Inhibited the development of edema 47 Human skin disease anti-inflammatory 51	HSV-118,28PI-328Smallpox Orthopoxvirus and COVID-1929Type A H1N1 (influenza virus)23,30,31,36HSV-231	Respiratory tract cold 26	Immunomodulatory activity 52
Cinnamon Cassia or Cinnamon from China	Cinnamomum cassia	Branches/bough, leaves (cinnamaldehyde, cinnamyl acetate, eugenol)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Reduce the inflammatory response after different kinds of stimuli 53	HSV-118Influenza virus 23 Type A H1N1 virus 30		Immunomodulatory effects 53
Citronella or Ceylon Citronella	Cymbopogon nardus	Leaves (citronellol, geraniol, citronellal, geranyl formate)	Reduced peripheral nerve excitability and inflammation 54	HSV-1 and PI-328		Strong depressant action 43
Citronella-java	Cymbopogon winterianus	Leaves (citronellol, geraniol, citronellal, citronellyl acetate)		HSV-1 and PI-328			Strong depressant action 43 Treatment of epilepsy and anxiety 55
Clove	Syzygium aromaticum (synonym: Eugenia caryophyllata)	Flower bud (eugenol, eugenol acetate, β-caryophyllene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Inhibited the development of edema 47	HSV-118,23,28HSV-223PI-328		Immunomodulatory activity (improvement in humor- and cell-mediated immune response mechanisms) 56
Copaiba	Copaifera ssp.	Oil-resin or balm (sesquiterpenes: β-caryophyllene, α-humulene, α-copaene, cadinene)	Inhibition of the activation and/or release of different inflammatory mediators 57 Reduced the carrageenan- induced edema and the release of inflammatory mediators 58 Inhibited the development of edema 47	HSV-118	Antiasthmatic activity 59	Immunomodulatory action 60
Cordia verbenacea (Erva-baleeira Brazil)	Varronia curassavica or Cordia verbenacea	Leaves (α-humulene, β-caryophyllene, α-pinene)	Inhibition of the activation and/or release of different inflammatory mediators 57 Reduced the carrageenan-induced edema and the release of inflammatory mediators 58	HSV-118	Pulmonary anti-inflammation 61	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Coriander	Coriandrum sativum	Fruits and seeds (coriandrol or linalool, geraniol, camphor)	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33 Anti-inflammatory pain and edema production, reduce the NO synthesis 43		Camphor antitussive activities 31	Immunomodulatory activity 62	Anticonvulsivant and anxiolytic activities GABAergic system 43
Eucalyptus	Eucalyptus globulus	Leaves (1,8 cineol, α-pinene, globulol)	Gastrointestinal inflammation and ulceration 32 Bacterial anti-inflammatory (Stenotrophomonas maltophilia, Streptococcus pneumoniae) 63 Bacterial anti-inflammatory (Porphyromonas gingivalis, and others) 64 Decreasing inflammatory cytokines 64	HSV-123,24,31,64HSV-223,24COVID-1929,65HPIVs 29 Type A H1N1 (influenza virus)30,36,64Haemophilus influenzae63,64Haemophilus parainfluenzae 63 Mumps virus 64 H9N2 AIV 66	Anti-inflammatory action in bronchial asthma, respiratory diseases32,67Rhinosinusitis, asthma, and cilia in respiratory tract 64	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Immunostimulating activity 32	Anxiety 68
Eucalyptus radiata	Eucalyptus radiata	Leaves (1,8 cineol, α-terpineol, α-pinene, sabinene)	Gastrointestinal inflammation and ulceration 32 Reduction of TNF-α and NO production 43	Paramyxovirus-mumps, COVID-19, Herpesvirus-6, HPIVs 29	Action in bronchial asthma 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Fennel	Foeniculum vulgare	Adult leaves (trans-anethol, cis-anethol)	Inhibitory effects against acute and subacute inflammatory diseases and type IV allergic reactions 69	HSV-118,23,28HSV-223PI-328
Frankincense or Olibanum	Boswellia carterii, Boswellia serrata (synonym: Boswellia sacra)	Resin (octyl acetate, octanol, α-pinene, incensole, elemene, β-caryophyllene)	Inhibition of the activation and/or release of different inflammatory mediators 57 Reduced the carrageenan-induced edema and the release of inflammatory mediators 58 Wound healing 70	HSV-118	Chronic obstructive pulmonary disease, bronchial asthma, acute lung injury, pulmonary infection, and pulmonary fibrosis 71	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Immunomodulatory effects 70	Anxiolytic, and antidepression70,72Symptoms of bowel syndrome patients 72
Gataria or Catnip or Catnep	Nepeta cataria	Branches/bough with leaves and flowers (nepetalactone, nepetalic acid, β-caryophyllene, geraniol, nerol, citronellol)	Reduced the carrageenan-induced edema and the release of inflammatory mediators58,73	HSV-118COVID-1973	Against lung damage caused by COVID-1973	Immune regulation 73
Geranium	Pelargonium graveolens	Branches/bough with leaves (citronellol, geraniol, linalool, geranial, citronellol formate, geraniol formate)	LPS-induced NO and PGE2 production in RAW 264.732Reduced peripheral nerve excitability and inflammation 54	Influenza type A (H1N1)30,56		Immune modulating effects no natural killer cells 74	Analgesic16,17Antidepressant activities, serotonergic route16,75Anxiolytic17,75,76Decrease in diastolic blood pressure 76
Ginger	Zingiber officinale	Rhizomes (zingiberene, bisabolene, curcumene, farnesene, ocimene)	Anti-inflamatory anti-edema effects77,78	HSV-1, HSV-223,31Caprine alphaherpesvirus 31	Bronchodilator effects 78	Immunomodulatory activity (improvement in humor- and cell-mediated immune response mechanisms) 56 Immunomodulator agent, number of total T lymphocytes and T helper cells de-creased 78	Mental relaxant 78
Hinoki cypress	Chamaecyparis obtusa .	Wood (bornyl acetate, α-pinene, carene, cadinene, muurolene)				Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Improves NK activity 37	Stimulated a pleasant mood status 79
Ho wood or Ho leaf	Cinnamomum camphora (chemotype linalool)	Leaves (linalool)	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33 Inflammatory pain and edema production, reduce the NO synthesis 43		Acute lung injury 80		Anticonvulsant16,43Analgesia 17 Anxiolytic activities GABAergic system17,43
Labdanum or Cistus	Cistus ladanifer	Branches/bough with leaves and flowers (α-pinene, camphene, bornyl acetate, limonene, γ-terpinene, terpinen-4-ol)		Paramyxovirus-mumps, Morbillivirus Paramyxoviridae, Varicellovirus HHV-329		Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Laurus	Laurus nobilis	Berries (1,8 cineol, linalool, α-terpineol, α-pinene, β-pinene)	Anti-inflammatory efficacy in inhibiting polyclonal stimulated cytokine production by unselected lymphocytes and LPS-stimulated monocytes 32 Analgesic and anti-inflammatory effect to edema, wound-healing activity, antiulcerogenic activity 81 Reduction of TNF-α and NO production 43	SmallpoxOrthopoxvirus 29 Inhibitory activity against SARS-CoV replication (COVID-19)29,81–83		Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Anticonvulsant activity, and sedative16,81
Lavandin	Lavandula intermedia	Branches/bough with flowers (linalool, borneol, camphor, linalyl acetate, bornyl acetate)	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33 Inflammatory pain and edema production, reduce the NO synthesis 43	HSV-118	Antitussive activities 31	Immunomodulatory effects 84	Anticonvulsivant and anxiolytic activities GABAergic system17,43
Lavender or Fine lavender or True lavender	Lavandula angustifolia	Branches/bough with leaves and flowers (linalool, linalyl acetate, lavandullyl acetate, lavandulol, terpinen-4-ol, ocimene, limonene)	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33	HSV-128Herpesvirus-6, HPIVs 29 Type A H1N1 (influenza virus)30,31	Anti-inflammatory asthma, antiallergic 85	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Higher IgA levels 37	Analgesic, antidepressant, calming, and hypnotic 16 Anticonvulsant16,82Sedative16,86Stimulatory, GABAergic 17 Relaxing effects16,42,87Anxiolytic activities GABAergic system16,43,68,88,89
Lavender spike	Lavandula latifolia	Branches/bough with leaves and flowers (1,8 cineol, linalool, α-terpineol, terpinen-4-ol, camphor)	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33 Reduction of TNF-α and NO production 43	HSV-123,24,31	Antitussive activities 31	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Lemon siciliano or Lemon	Citrus limon (synonym: Citrus limonum)	Fruit peel/pericarp (limonene, α-pinene, β-pinene, citronelal, citral b )	Inhibitor of leukotriene production 32	HSV-123,24,31	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Neuroimmunomodulatory 16 Immunostimulating activity CD4/CD8 T cell values and NK cell activity32,37,38	Antidepressant16,38Mentally stimulating, reviving 16 Analgesia, anxiolytic 17 Positive mood 37
Lemon verbena	Lippia citriodora (synonym: Aloysia citriodora)	Leaves (citral, b geraniol, α-terpineol, β-caryophyllene, nerol)	Inhibitor of leukotriene production 32 Reduce paw edema and leukocyte migration 43	HSV-118,28PI-328YFV, DENV-1, DENV-2, DENV-3, DENV-4, and YFV 17 DD 31	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32		Sedative, antidepressant 16
Lemongrass	Cymbopogon citratus	Leaves (citral, b geraniol, myrcene)	Inhibitor of leukotriene production 32 Anti-inflammatory activity inhibition of the transcription factor NF-κB 90 Reduces edema and leukocyte migration 43 Anti-inflammations by lipopolysaccharide-stimulated macrophages 55	HSV-123,24,28,31PI-328Oral thrush in patients who tested positive to HIV/AIDS 55	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Immunomodulatory effect on cytokines production 90	Sedative 16 Antidepressant activities16,75Serotonergic route, generalized anxiety disorder, anxiolytic55,75,90
Lemongrass-india	Cymbopogon flexuosus	Leaves (citral b )	Inhibitor of leukotriene production 32 Anti-inflammatory activity inhibition of the transcription factor NF-κB 90 Reduces edema and leukocyte migration 43	HSV-1, PI-328Type A H1N1 (influenza virus)30,31,36	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Immunomodulatory effect on cytokines production 90	Sedative, antidepressant 16
Litsea cubeba or May Chang	Litsea cubeba	Branches/bough, leaves with fruits (citral, b linalool, nerol, linalool, geraniol, limonene, myrcene)	Inhibitor of leukotriene production 32 Reduces edema and leukocyte migration 43	HSV-1, PI-328	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Sedative, antidepressant 16
Manuka or Tea Tree from New Zealand	Leptospermum scoparium	Branches/bough and leaves (β-caryophyllene, leptospermone, calamenene, α-pinene, cadina diene, selinene)		HSV-118		Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Marjoram	Origanum majorana	Branches/bough, leaves, flowers (terpinen-4-ol, linalool, linalyl acetate, γ-terpinene, α-terpinene, β-caryophyllene)	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33 Anti-inflammatory by mediator production by activated human monocytes 91	HSV-118,23,24,28,31HSV-231		Higher IgA levels 37	Analgesic and anxiolytic16,17Sedative 16
Melissa or Lemon balm	Melissa officinalis	Leaves (nerol, isopulegol, citral, b β-caryophyllene, citronelal, geraniol)	Inhibitor of leukotriene production 32 Reduce paw edema and leukocyte migration 43 Reduced peripheral nerve excitability and inflammation 54 Anti-inflammatory properties by inhibition of edema and pain 92	HSV-118,23,24,28,31HSV-223,24,31PI-328Type A H1N1 (influenza virus) 30 AIV H9N231	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32		Anxiolytic, calming, hypnotic, sedative, CNS depressant, analgesic 16 Management of agitation in severe dementia, better quality of emotional life parameters 93 Anti-agitation properties, depressant effects on neural activity 94
Myrrha	Commiphora myrrha	Resin (sesquiterpenes: curzerene, copaene, furanoeudesma 1,3-diene, β-elemene)	Anti-inflammatory properties by inhibition of edema and pain 26 Wound healing 35			Immunomodulatory 95	Improved memories 35
Niaouli	Melaleuca quinquenervia	Leaves (1,8 cineol, α-terpineol, terpinen-4-ol, viridiflorol, nerolidol, α-pinene, β-pinene, β-caryophyllene)	Inhibitor of leukotriene production 32 Reduction of TNF-α and NO production 43 Anti-inflammatory by mediator production by activated human monocytes 91	HSV-118COVID-19 and HPIVs 29	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Origanum	Origanum vulgare (synonym: Origanum compactum)	Branches/bough with leaves (carvacrol, thymol, linalool, terpinen-4-ol, α-terpineol, camphor, α-myrcene, β-myrcene, para-ocimene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Inhibited the development of edema 47 Reduction of TNF-α and NO production 43 Anti-inflammatory by mediator production by activated human monocytes 91	HSV-118,28COVID-19 and HIV 29 PI-328Parainfluenza type 3 virus 30 YFV 31 YFV, NDV 83	Antitussive activities 31
Origanum wild	Origanum munitiflorum	Branches/bough with leaves (carvacrol, linalool, β-caryophyllene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27	HSV-118,28PI-328
Palmarosa	Cymbopogon martinii	Leaves, branches/bough (geraniol, linalool, geranyl acetate, geranyl formate, β-caryophyllene)	Inhibitor of leukotriene production 32 Reduced peripheral nerve excitability and inflammation 54	HSV-118Morbillivirus Paramyxoviridae, Varicellovirus HHV-329	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32		Anticonvulsivant 16 Analgesia, anxiolytic 17
Pau-rosa	Aniba rosaeodora	Leaves and branches/bough (linalool, linalool oxide, α-pinene, β-pinene) [Previously: wood of the tree]	Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33	HSV-1 and PI-328	Antiasthmatic activity 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Anticonvulsivant 16 Analgesia, anxiolytic 17
Peppermint or Mentha or True Mentha	Mentha piperita	Leaves (menthol, menthone, menthol acetate, neomenthol, 1,8 cineol, isomenthone, terpinen-4-ol, pulegone, limonene)	Inhibitor of leukotriene production 32	HSV-123,24,28,31HSV-223,24,31PI-328H9N2 AIV 66	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32 Antitussive activities 31 Improved treatment of infiltrative pulmonary tuberculosis 42	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Stimulatory 16
Pepper from Jamaica	Pimenta dioica (synonym: Pimenta officinalis)	Branches/bough with leaves and fruits (eugenol, methyl-eugenol, 1,8 cineol, α-phellandrene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27	HSV-118,23,28HSV-223PI-328		Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Petitgrain	Citrus aurantium	Leaves (linalool, linalyl acetate, myrcene)	Decrease pro-inflammatory cytokines 22 Anti-inflammatory (NMDA receptors, glutamate release, carrageenin-induced) 33	HSV-1 and PI-328		Improve immune function CD4/CD8 T cell values and NK cell activity37,38	Anxiolytic17,22,40Analgesia 17 Sedative effects 40 Antidepressing 38
Ravintsara	Cinnamomum camphora (chemotype 1,8 cineol)	Leaves (1,8 cineol, α-terpineol, linalool, camphor, α-pinene, β-pinene, terpinyl acetate, linalyl acetate)	Gastrointestinal inflammation and ulceration 32	Paramyxovirus-mumps, Morbillivirus Paramyxoviridae, Varicellovirus HHV-3, and HIV 29	Anti-inflammatory action in bronchial asthma 32 Antitussive activities 31	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Roman chamomile	Chamaemelum nobile or Anthemis nobilis	Flowers and branches (α-bisabolol, A and B-bisabolol oxides, farnesene, α-pinene, angelate ester)	Anti-inflammatory dermatological agent 96	HSV-118Herpesvirus-6, and HPIVs 29	Chronic bronchial asthma 97	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Analgesic, hypnotic, relaxing 16 Sedative16,35Antidepression, and anxiolytic 50 Stimulatory GABAergic 17
Rose	Rosa damascena	Flower petals (citronellol, geraniol, linalool)	Decrease pro-inflammatory biomarkers 98		Trachea relaxant effect 98	Potent immunomodulatory 98	Antidepressant, and relaxing 16 Sedative16,35Analgesia 17 Anxiolytic17,35,68
Rosmarinus or Alecrim	Rosmarinus officinalis	Branches/bough (chemotype camphor)(chemotypes: 1,8 cineol, verbenone)		X (22, 23: HSV-1), (27: HSV-1)52 HSV-123,24,28,31	Antitussive activities 31	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Stimulatory16,99Mood effects 99
Sage or Salvia or Salvia dalmaciana	Salvia officinalis	Branches/bough, rhizomes, leaves, and flowers (α-thujone, β-thujone, 1,8-cineol, α-terpineol, terpine-4-ol, camphor, β-caryophyllene, bornyl acetate)		HSV-118,28	Antitussive activities 31	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Cholinergic, stimulatory, GABAergic16,17Proconvulsivante 17
Sandalwood	Santalum album	Tree bark or wood (santalol, santalal)	Urinary infection action 35	HSV-1, and HSV-223,31Type A (H3N2) influenza virus 30			Anxiolytic and sedative-hypnotic effects 50
Satureja or Segurelha	Satureja cuneifolia	Branches/bough with leaves and flowers (carvacrol, thymol e para-ocimene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Antifungal activity Candida species 100	HSV-128Parainfluenza type 3 virus PI-328,30	Antitussive activities 31
Spearmint or Mint or Green mint	Mentha spicata	Branches/bough with leaves (carvone, limonene, 1,8 cineol)		HSV-1 and PI-328	Respiratory system relaxant effect 101	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Sedative, antidepressant effects 102
Star anise	Illicium verum	Seeds (trans-anethole, α-terpineol, estragole, limonene)		HSV-118,23,31HSV-223,31		Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Sweet orange	Citrus sinensis	Fruit peel or pericarp (limonene, α-pinene, β-pinene, sabinene, perilla alcohol, myrcene, linalool)	Decrease pro-inflammatory cytokines 22 Inhibitor of leukotriene production, reduce pro-inflammatory cytokine 32	COVID-1923,44	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Immunomodulatory effect 32 Improve immune function CD4/CD8 T cell values and NK cell activity37,38Higher IgA levels 37	Sedative effect 20 Anxiolytic effects20,22,103–105Improves the depressive state 38
Tahiti lemon	Citrus latifolia	Fruit peel or pericarp (limonene, geranial, β-bisabolene)	Inhibitor of leukotriene production, reduce pro-inflammatory cytokine 32 Reducing PGE2, production in macrophages and IL-1α cytokine 106		Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Immunomodulatory effect 32 Improve immune function CD4/CD8 T cell values and NK cell activity37,38	Improves the depressive state 38
Tarragon or Garden wormwood or Dragon herb	Artemisia dracunculus	Leaves and branches/bough with flowers (methyl-chavicol or estragole, ocimene)	Antifungal infection (Cryptococcus) 35 Bacterial anti-inflammatory (Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus faecalis, Yersinia enterocolitica) 35	Hepatitis B virus 29
Tea-tree or Melaleuca	Melaleuca alternifolia	Leaves (terpinen-4-ol, α-terpineol, isomers of terpinene, thujone, 1,8 cineol, globulol, viridiflorol, limonene)	Reduction of TNF-α and NO production 43 Anti-inflammatory by mediator production by activated human monocytes 91	HSV-1 and HSV-223,24,31Paramyxovirus-mumps, Morbillivirus Paramyxoviridae, Varicellovirus HHV-3 and HIV 29 Type A H1N1 (influenza virus)30,83Influenza A⁄PR⁄8 virus subtype H1N1 and type A (H11N9) virus30,31	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15 Immunomodulatory agent 107	GABAergic, proconvulsivante 17
Thuja-apple or Red Cedar or Cedar leaf	Thuja plicata	Leaves (thujone, α-pinene and β-pinene, myrcene)		Influenza viruses, Rhinovirus, Adenovirus, and HSV-1 and HSV-2108		Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	GABAergic, proconvulsivante 17
Thyme	Thymus vulgaris (chemotype thymol)(chemotypes: linalool, tuianol, geraniol, borneol)	Branches/bough with leaves (thymol, carvacrol, 1,8 cineol, para-ocimene, γ-terpinene, tuianol, linalool)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Inflammatory skin disorders 109	HSV-118,23,28,31HSV-223,31PI-328HIV and COVID-1929Type A (H1N1) virus30,31,36Parainfluenza type 3 virus 30	Antitussive activities31,109Bronchitis 109	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15	Stimulatory, GABAergic 17
Thyme wild	Thymus serpyllum (synonym: Thymus vulgaris chemotype limonene)	Leaves and flowers (carvacrol, thymol, limonene, para-ocimene, β-caryophyllene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27 Inhibition of the activation and/or release of different inflammatory mediators 57	HSV-118,28PI-328Parainfluenza type 3 virus 30	Antiasthmatic activity, chronic bronchitis, and allergic rhinitis 32 Antitussive activities 31	Phytoncides (increase cytolytic activity natural killer NK-92MI cells) 15
Winter savory	Satureja montana (synonym: Saureja hortensis, Satureia montana, Satureia hortensis)	Branches/bough with flowers (carvacrol, thymol, eugenol, para-ocimene, γ-terpinene, β-caryophyllene)	Bacterial anti-inflammatory (Bacillus cereus, and others) 27	HSV-118,23,28HSV-223PI-328HIV and COVID-1929Parainfluenza type 3 virus 30	Antitussive activities 31

a

The action of EO is due to the synergy of all its components and not just the action of its major components.

b

Citral is a mix of the geranial and neral components.

A⁄PR⁄8, influenza virus type A/PR/8; AIV, avian influenza virus; CNS, central nervous system; DENV, dengue virus; EO, essential oils; GABAergic, Y-Aminobutyric Acid (GABA) System; H1N1, influenza type A virus; H9N2, avian influenza A virus; HHV-3, varicellovirus; HPIV, human parainfluenza viruses; HSV-1, herpes simplex virus 1; HSV-2, herpes simplex virus 2; IL-1α, interleukin 1 alpha; LPS, lipopolysaccharide; NDV, Newcastle disease virus; NF-κB, nuclear factor kappa B; NK, natural killer cell; NK-92MI, natural killer cell 92MI Type; NMDA, N-Methyl-D-Aspartate Receptor; NO, nitric oxide; PGE2, prostaglandin E2; PI-3, parainfluenza Type-3; RAW, macrophages cells type; SARS-CoV, Severe Acute Respiratory Syndrome Coronavirus; TNF-α, Tumor Necrosis Factor-A Human; YFV, yellow fever virus; YFV 17 DD, yellow fever 17DD Virus.

Results and Discussion

Table 1 presents a review of research that directs the therapeutic of EO to anti-inflammatory action, antiviral action, respiratory health action, immunological health action, mental and emotional health action.

The methodological systematization of best practice guidelines of aromatherapy to restore smell starts by filling out the anamnesis form (Box 1). Boxes 2 and 3 describe the preparation of the inhaler apparatus. Boxes 4 and 5 describe the dynamics of the inhalation procedure. Table 2 shows the summary of EO activity.

Box 1.

Anamnesis Form: Olfactive and/or Taste Loss

A. Name:

B. Age:

C. Gender:

D. Date positive for the COVID-19 virus:

E. Date negative for the COVID-19 virus:

F. Report of the main olfactory symptoms:anosmia (selective, partial, or total loss of aroma):phantosmia (sensing aroma that is not in the environment):hyperosmia (sensing too much a type of aroma):hyposmia (sensing a type of aroma diminished):parosmia (sensing a scent that belongs to another object):cacosmia (sensing a fetid aroma in something that doesn't have it):

G. Report of the main taste symptoms:ageusia (selective, partial, or total loss of flavour):phantogeusia (sensing the taste that is not in the environment):hypergeusia (sensing too much a type of flavour):hypogeusia (sensing a type of flavor diminished):parageusia (sensing a taste that belongs to another food):

H. Possible cause of the contamination or type of exposure that caused the contamination (the higher the viral load, the symptoms may be more pronounced):

I. Tick the symptoms you had during COVID-19:fever ( )shortness of breath ( )tiredness ( )headache ( )diarrhea ( )dry cough ( )others symptom: .….….….….….….….….….….…… .….……how many days did these symptoms remained?Has the patient been hospitalized?yes ( ), for .….. daysno ( )

J. Does the patient have one of these aggravating or comorbid conditions?smoker ( )obesity ( )diabetes ( )sedentary lifestyle ( )heart disease ( )chronic respiratory disease, asthma ( )immunodepressed ( )cancer ( )others: .….….….….….….….….….….….… .….….….….….

L. Please write here any other information you want to report: .….….….….….….….….….…

Box 2.

Inhaler Preparation

A. The use of inhalers with EO, daily and weekly (Box 3):

a) First week: the kit consists of one EO (inhaler 1) or one hydrosol (wash both the nasal and buccal mucosal) with anti-inflammatory activity, and one EO with antiviral activity (inhaler 2). Choose these EO from Table 2.

b) Second week: the kit consists of one EO with respiratory health activity (inhaler 3), one EO with immunological health activity (inhaler 4) and one EO with mental and emotional health activity (inhaler 5). Choose these EO from Table 2.

c) Third week: choose different EO from Table 2 to perform olfactory training. The kit consists of one EO with respiratory health activity (inhaler 6), one EO with immunological health activity (inhaler 7) and one EO with mental and emotional health activity (inhaler 8).

d) Fourth week: choose different EO from Table 2 to perform olfactory training. The kit consists of one EO with respiratory health activity (inhaler 9), one EO with immunological health activity (inhaler 10) and one EO with mental and emotional health activity (inhaler 11)

B. Inhalation apparatus (Fig. 2):

a) Individual inhaler apparatus containing cotton or filter paper.

b) Write the name of the EO on a label and attach it to the inhaler.

c) Add 1 mL, or 25 drops, of pure EO (undiluted) in each inhaler.

d) Perform the inhalation procedure and close the inhaler tightly. Store in a cool place (below 23°C), out of direct sunlight.

e) Use each inhaler 5 days a week. After that, discard the inhaler apparatus and use the cotton or filter paper to scent some drawers in your closet.

f) This guideline uses 11 inhaler apparatuses in 1 month

IMPORTANT: each inhaler apparatus contains one EO. A blend or synergy with EO is NOT carried out

EO, essential oils.

FIG. 2.

Apparatuses for the olfactory training: (A) three types for inhaling the essential oils (1: cotton to put EO; 2: bottle to put cotton inside; 3: bottle top to close it after the use); (B) one type for washing with hydrosol (1: bottle to put the hydrosol inside; 2: valve to wash both the nasal and buccal mucosal; 3: bottle top to close it after the use).

Box 3.

Dynamics of the Use of Inhalers with Essential Oils, Daily and Weekly

Week	EO activity	Day 1	Day 2	Day 3	Day 4	Day 5	Day 6	Day 7
1st	Anti-inflammatory	Inhaler 1 or wash hydrosol	Inhaler 1 or wash hydrosol	Inhaler 1 or wash hydrosol	Inhaler 1 or wash hydrosol	Inhaler 1 or wash hydrosol	Free	Free
	Antiviral	Inhaler 2	Inhaler 2	Inhaler 2	Inhaler 2	Inhaler 2
2nd	Respiratory health	Inhaler 3	Inhaler 3	Inhaler 3	Inhaler 3	Inhaler 3	Free	Free
	Immunological health	Inhaler 4	Inhaler 4	Inhaler 4	Inhaler 4	Inhaler 4
	Mental and emotional health	Inhaler 5	Inhaler 5	Inhaler 5	Inhaler 5	Inhaler 5
3rd	Respiratory health	Inhaler 6	Inhaler 6	Inhaler 6	Inhaler 6	Inhaler 6	Free	Free
	Immunological health	Inhaler 7	Inhaler 7	Inhaler 7	Inhaler 7	Inhaler 7
	Mental and emotional health	Inhaler 8	Inhaler 8	Inhaler 8	Inhaler 8	Inhaler 8
4th	Respiratory health	Inhaler 9	Inhaler 9	Inhaler 9	Inhaler 9	Inhaler 9	Free	Free
	Immunological health	Inhaler 10	Inhaler 10	Inhaler 10	Inhaler 10	Inhaler 10
	Mental and emotional health	Inhaler 11	Inhaler 11	Inhaler 11	Inhaler 11	Inhaler 11
5th	_	Free	Free	Free	Free	Free	Free	Free

Box 4.

Training Frequency and Process

A. Training frequency (Box 5):

a) This guideline provides olfactory training for 4 weeks, changing the essentials oils every week.

b) At the end of the 4th week, stop for 1 week.

c) Perform inhalation twice a day, for 5 consecutive days, using the same inhaler.

d) Then stop the performed inhalation for 2 days.

e) Re-evaluate the olfactory and gustatory sensation. If necessary, restart all the process of the olfactory training described in this guideline

B. Training process:

a) Inhale with each blowhole separately, keep the oral cavity closed.

b) Do 3 inhalations slowly with one nostril, while the other nostril remains covered with the finger. Invert and change the nostrils (Do 3 inhalations slowly with the other nostril, while the first nostril remains covered with the other finger).

c) Aspirate 3 times through the oral cavity, keeping the 2 nostrils closed.

d) Aspirate 3 times through the oral cavity, keeping the 2 nostrils open

Box 5.

Dynamic of Training Frequency Twice a Day

Week	Day 1	Day 2	Day 3	Day 4	Day 5	Day 6	Day 7
1st	Morning training	Morning training	Morning training	Morning training	Morning training	Free	Free
	Evening training	Evening training	Evening training	Evening training	Evening training
2nd	Morning training	Morning training	Morning training	Morning training	Morning training	Free	Free
	Evening training	Evening training	Evening training	Evening training	Evening training
3rd	Morning training	Morning training	Morning training	Morning training	Morning training	Free	Free
	Evening training	Evening training	Evening training	Evening training	Evening training
4th	Morning training	Morning training	Morning training	Morning training	Morning training	Free	Free
	Evening training	Evening training	Evening training	Evening training	Evening training
5th	Free	Free	Free	Free	Free	Free	Free

Table 2.

Summary of Essential Oils Activity

EO		Activity
Popular name	Botanical name	Anti-inflammatory a	Antiviral	Respiratory health	Immunological health	Mental and emotional health
Alojan b or Ajowan or Ajwain or Caraway or Fighter oil	Trachyspermum ammi	X	X	X	X
Anethum or Endro or Dill	Anethum graveolens	X	X	X	X	X
Basil	Ocimum basilicum	X	X	X
Bay Pepper b or Bay Rum	Pimenta racemosa	X	X		X	X
Bergamot	Citrus bergamia	X	X	X	X	X
Bitter orange	Citrus aurantium	X	X	X	X	X
Black cumin b	Nigella sativa	X	X	X	X	X
Black Pepper	Piper nigrum	X	X	X	X
Blue chamomile or German chamomile	Chamomilla matricaria (synonyms: Chamomilla recutita, Matricaria recutita)	X	X		X	X
Cajeput	Melaleuca cajuputi	X	X	X	X
Ceylon cinnamon b	Cinnamomun zeylanicum (synonym: Cinnamomum verum)	X	X	X	X
Cinnamon Cassia b or Cinnamon from China	Cinnamomum cassia	X	X		X
Citronella or Ceylon Citronella	Cymbopogon nardus	X	X		X
Citronella-java	Cymbopogon winterianus		X			X
Clove b	Syzygium aromaticum (synonym: Eugenia caryophyllata)	X	X		X
Copaiba	Copaifera ssp	X	X	X	X
Cordia verbenacea (Erva-baleeira Brazil)	Varronia curassavica or Cordia verbenacea	X	X	X	X
Coriander	Coriandrum sativum	X		X	X	X
Eucalyptus b	Eucalyptus globulus	X	X	X	X	X
Eucalyptus radiata	Eucalyptus radiata	X	X	X	X
Fennel	Foeniculum vulgare	X	X
Frankincense or Olibanum	Boswellia carterii (synonym: Boswellia sacra)	X	X	X	X	X
Gataria or Catnip or Catnep	Nepeta cataria	X	X	X	X
Geranium	Pelargonium graveolens	X	X		X	X
Ginger	Zingiber officinale	X	X	X	X	X
Hinoki	Chamaecyparis obtusa				X	X
Ho wood or Ho leaf	Cinnamomum camphora (chemotype linalool)	X		X		X
Labdanum or Cistus	Cistus ladanifer		X		X
Laurus	Laurus nobilis	X	X		X	X
Lavandin	Lavandula intermedia	X	X	X	X	X
Lavender or Fine lavender or True lavender	Lavandula angustifolia	X	X	X	X	X
Lavender spike	Lavandula latifolia	X	X	X	X
Lemon siciliano or Lemon	Citrus limon (synonym: Citrus limonum)	X	X	X	X	X
Lemon verbena	Lippia citriodora (synonym: Aloysia citriodora)	X	X	X		X
Lemongrass	Cymbopogon citratus	X	X	X	X	X
Lemongrass-india	Cymbopogon flexuosus	X	X	X	X	X
Litsea cubeba or May Chang	Litsea cubeba	X	X	X	X	X
Manuka or Tea Tree from New Zealand	Leptospermum scoparium		X		X
Marjoram	Origanum majorana	X	X		X	X
Melissa or Lemon balm	Melissa officinalis	X	X	X		X
Myrrha	Commiphora myrrha	X			X	X
Niaouli	Melaleuca quinquenervia	X	X	X	X
Origanum b	Origanum vulgare (synonym: Origanum compactum)	X	X	X
Origanum wild b	Origanum munitiflorum	X	X
Palmarosa	Cymbopogon martinii	X	X	X		X
Pau-rosa	Aniba rosaeodora	X	X	X	X	X
Peppermint b or Mentha or True Mentha	Mentha piperita	X	X	X	X	X
Pepper from Jamaica b	Pimenta dioica (synonym: Pimenta officinalis)	X	X		X
Petitgrain	Citrus aurantium	X	X		X	X
Ravintsara b	Cinnamomum camphora (chemotype 1,8 cineol)	X	X	X	X
Roman chamomile	Chamaemelum nobile or Anthemis nobilis	X	X	X	X	X
Rose	Rosa damascena	X		X	X	X
Rosmarinus or Alecrim	Rosmarinus officinalis		X	X	X	X
Sage b or Salvia or Salvia dalmaciana	Salvia officinalis		X	X	X	X
Sandalwood	Santalum album	X	X			X
Satureja b or Segurelha	Satureja cuneifolia	X	X	X
Spearmint or Mint or Green mint	Mentha spicata		X	X	X	X
Star anise	Illicium verum		X		X
Sweet orange	Citrus sinensis	X	X	X	X	X
Tahiti lemon	Citrus latifolia	X		X	X	X
Tarragon b or Garden wormwood or Dragon herb	Artemisia dracunculus	X	X
Tea-tree or Melaleuca	Melaleuca alternifolia	X	X	X	X	X
Thuja-apple b or Red Cedar or Cedar leaf	Thuja plicata		X		X	X
Thyme	Thymus vulgaris (chemotype thymold)	X	X	X	X	X
Thyme wild	Thymus serpyllum (synonym: Thymus vulgaris chemotype limonene)	X	X	X	X
Winter savory b	Satureja montana (synonym: Saureja hortensis, Satureia montana, Satureia hortensis)	X	X	X

a

Exceptionally, EO or Hydrosol can be used. If Hydrosol is chosen, then the procedure is to wash both the nasal and buccal mucosal with it.

b

Avoid use in children under 6 years old and in the elderly over 80 years old, due to the potential toxicity of its major components. ¹¹⁰

Choose two EO from Table 2, for inhalation during the 1st week. Choose three EO, from Table 2, for inhalation during the 2nd week. For inhalation during the 3rd and 4th weeks, choose different EO from Table 2, according to action. Use a new inhaler containing EO every single week; this will ensure that the EO is inhaled in its full composition. After each day of olfactory training, complete the forms in Boxes 6 and 7 respectively. Box 8 contains additional information to expand the application of this guideline, and Box 9 shows examples of EO selected for this training, according to summary Table 2.

Box 6.

Records of the First Week Procedure

Week: 1st
EO
Anti-inflammatory(write here the name of the chosen EO or hydrosol)	Antiviral(write here the name of the chosen EO)
Note what occurs during the procedure here
DAY 1:
DAY 2:
DAY 3:
DAY 4:
DAY 5:
1st evaluation of smell and taste:
Further report:

Box 7.

Records of the Following Weeks Procedure

Weeks*: 2nd – 3rd – 4th(*choose 3 different EO each week)
EO
Respiratory health(write here the name of the chosen EO)	Immune health(write here the name of the chosen EO)	Mental and emotional health(write here the name of the chosen EO)
Note what occurs during the procedure here
DAY 1:
DAY 2:
DAY 3:
DAY 4:
DAY 5:
Evaluation of smell and taste: 2nd – 3rd – 4th
Further report:
ONE WEEK BREAKReport of what happens during this week:

Box 8.

Complementary Actions

a) Maintain the patient calm and hopeful during the olfactory training of this guideline.

b) Offer as many aromas to the patient as possible: cigarette smoke, gasoline, onion, chocolate, soap, banana, fried food, boiled egg, barbecue or roast, softeners, garlic, honey, coffee, and others.

c) After the aroma has been perceived, try to minimize it to observe the olfactory detection limit (threshold).

d) Offer to the patient bottles with different aromas, however in one of them, do not add aromatic substance, in order to evaluate the placebo effect.

e) Variations of this guideline can be implemented according to the experience of the aromatherapist and the needs of the patient

Box 9.

Two Examples of Essential Oils Chosen from Review Table 2 for the Olfactory Training

Week	Hydrosol or EO	Wash or inhaler	Activity
Example 1
1st	Lavender hydrosol	Nasal and buccal mucosa washing 1	Anti-inflammatory
	Eucalyptus EO	Inhaler 2	Antiviral
2nd	Ginger EO	Inhaler 3	Respiratory health
	Geranium EO	Inhaler 4	Immunological health
	Bergamot EO	Inhaler 5	Mental and emotional health
3rd	Frankincense EO	Inhaler 6	Respiratory health
	Blue chamomile EO	Inhaler 7	Immunological health
	Bay pepper EO	Inhaler 8	Mental and emotional health
4th	Ho wood EO	Inhaler 9	Respiratory health
	Laurus EO	Inhaler 10	Immunological health
	Lemon siciliano EO	Inhaler 11	Mental and emotional health
5th	_	_	_
Example 2
1st	Roman chamomile hydrosol	Nasal and buccal mucosa washing 1	Anti-inflammatory
	Ravintsara EO	Inhaler 2	Antiviral
2nd	Peppermint EO	Inhaler 3	Respiratory health
	Petitgrain EO	Inhaler 4	Immunological health
	Palmarosa EO	Inhaler 5	Mental and emotional health
3rd	Niaouli EO	Inhaler 6	Respiratory health
	Litsea cubeba EO	Inhaler 7	Immunological health
	Lemon verbena EO	Inhaler 8	Mental and emotional health
4th	Thyme EO	Inhaler 9	Respiratory health
	Eucalyptus radiata EO	Inhaler 10	Immunological health
	Bitter orange EO	Inhaler 11	Mental and emotional health
5th	_	_	_

This best practice guidelines of aromatherapy for olfactory restoration were compiled based on a review of research that demonstrated the bioactivity of the components of EO individually, as well as their interaction, which is called the synergistic effect of the EO.^110–113 This guideline is safe regarding adverse effects and toxicity. ¹¹⁴ Currently, the greatest demand is due to the sequelae of COVID-19.^24,115 However, it can be used for a loss or decrease in smell or taste caused by other factors, such as psychotropic medications, chronic rhinitis and sinusitis, neurological pathologies, cancer treatments, postinfectious and posttraumatic olfactory loss, older people, and other causes.^13,116

It can be observed that the olfactory and gustatory perception improve after 1 month that this guideline is applied. There are researchers though, showing that the average time is 3 months, and it may extend up to 8 months.^{8,92,117–119}

There are different methodologies for olfactory training. The methodology showed in this guideline is based on the references cited in this work, which consider the benefit of the variety of stimuli to the olfactory receptors, resulting from different molecular structures in different proportions. This is the main characteristic of EO from the various plant species suggested in Table 2.

The methodology used is aimed at reestablishing the olfactory sensation, however the consequences of the disease COVID-19 also cause losses in other areas of health. Thus, according to the review shown in Table 1, there is the possibility that the inhalation of EO can improve other areas of health, such as respiratory, immune, mental, and emotional systems. We call this mechanism the integrative activity of EO.

Conclusion

This study did not seek the exclusive and deep therapy and treatment of a disease. Instead, the best practice guidelines of aromatherapy to restore the sense of smell including the systematization of the methodology of the sequence of EO for inhalation were based on the research accessed through the presented review. In this way, this guideline met a need around integral health—immunological, respiratory, mental, and emotional—helping to restore the sense of smell and taste.