What about antiviral essential oils?
At the time of writing this article, there is no known cure for COVID-19 (although many possibilities are being tested), and there is currently no research into the effect essential oils may have on this particular virus. We are therefore not suggesting any treatment for SARS-CoV-2 infection with essential oils. Current standard of care for COVID-19 is supportive only.
Essential oils considered to be “antiviral” are not universal virus killers. Before we explain the existing research on “antiviral essential oils”, it is important to clarify the difference between virucidal and antiviral. “Antiviral” means that a compound inhibits the proliferation of a virus, while “virucidal” means a virus is destroyed or deactivated. In many instances, essential oils may be effective in killing one specific virus, but not another. Tea tree (Melaleuca alternifolia) essential oil inhibits the proliferation of influenza viruses inside cells (making it antiviral), but only modestly inhibits HSV-1 and HSV-2 (Garozzo et al 2009). Tea tree essential oil was not able to inhibit proliferation of the non-enveloped viruses poliovirus 1, adenovirus 2, echovirus 9, and Coxsackie B1 (Garozzo et al 2009). Much of the existing research on antiviral essential oils is on viruses that cause skin disease (herpes simplex I and II: HSV-1 and HSV-2), which has little relevance to viruses that cause respiratory tract infections.
In addition, finding research for antiviral activity does not equate to finding an “essential oil recipe for the virus”. For example, an in vitro/in vivo study examining an avian coronavirus that causes upper respiratory infections in chickens and other small birds worldwide showed that a proprietary compound showed virucidal activity and was effective in controlling coronavirus-related bronchitis in chickens (Jackwood et al 2010). The manufacturers report the compound contains botanical oleoresins and essential oils, but do not reveal the formulation. Another in vitro study examining the same avian coronavirus found that ethanol extracted plant material could interfere with the coronavirus infection. The most successful were ethanol extractions (not distilled essential oils) from peppermint (Mentha piperita), thyme (Thymus vulgaris), and a plant called showy tick-trefoil (Desmodium canadense) (Lelešius et al 2019). However, as mentioned above, this does NOT translate into any proven effect.
The closest to an applicable study is an in vitro study examining SARS-CoV (the 2002/2003 outbreak virus) and the effect of several essential oils. The authors report that a distilled oil extracted from Laurus nobilis berries was an effective virucidal against SARS-CoV (Loizzo et al 2008). The L. nobilis berries were sourced from a region in Lebanon, and the essential oil contained β-ocimene, 1,8-cineole, α-pinene, and β-pinene as the main constituents. This essential oil also contained eremanthin and dehydrocostus lactone as minor constituents at 3.65% and 7.57%, respectively (Liozzo et al 2008). These compounds are somewhat unusual in essential oils, but at least one in vitro study found that dehydrocostus lactone had activity against hepatitis B virus, an enveloped DNA virus (Chen et al 1995). However, laurel berry essential oil is not commercially available, and laurel leaf essential oil is not the same substance. It is possible that the oil used was a combination of essential oil and fatty oil made from Laurel berries by traditional methods, since only 56% of volatile compounds were identified (Tisserand and Young 2012, p322).
Research into coronaviruses may eventually address the antiviral efficacy of essential oils, but to date, in vitro data on the antiviral and virucidal activity of essential oils is limited, and in vivo human data is non-existent. As such, the specific mechanisms that coronaviruses use is poorly understood. SARS-CoV-2 is the most recent outbreak, which means even less is known about this coronavirus.
What can we learn about essential oils from research on other viruses?
The limited research available suggests that enveloped viruses are inactivated by some essential oils and their constituents, while non-enveloped viruses like Coxsackie B1 virus and human papilloma viruses (HPV), are not. Because there is no clinical research looking at coronaviruses and essential oils, using influenza as a proxy may provide some insights. Like influenza, coronaviruses are enveloped viruses and upon endosome-mediated cell entry, must be uncoated to enter the cytoplasm. You can think about this like a safe. In order to get to the money inside, you must first know the combination to the lock. Enveloped viruses must have that envelope removed for the inner part of the viral particle to enter the cytoplasm of the host cell, where it can reproduce. This mechanism (viral uncoating) has been well characterized for influenza, and you can read more about the essential oils and chemical constituents that affect influenza HERE. Coronaviruses affect the respiratory tract as does influenza, and also cause “cytokine storms”, followed by pneumonia, and sometimes death.
Suggestions in the Becker 2017 influenza article were based on research into the biology of influenza, and the interactions of essential oils and chemical constituents with multiple viral mechanisms of infection (Becker 2017). As discussed in Becker 2017, influenza viral uncoating occurs as the pH drops inside the endosome and the receptor-bound influenza protein undergoes a conformational change, allowing the virus contents to enter the host cell cytoplasm. In the case of influenza, a number of essential oils and their constituents interfere with this process in vitro, but the significance for influenza patients is unlikely (Becker 2017). The mechanism for uncoating of coronaviruses is unclear, but it differs from the mechanism used by influenza due to the difference in viral protein content, and we cannot assume that the same compounds interfere with coronaviruses at this step. The proteins involved in influenza host cell exit (namely NA) are not found on SARS-CoV-2.
The host’s innate immunity is provoked upon influenza infection, and a cascade of inflammatory pathways are initiated. In addition, a process called autophagy is triggered within the host cell. Autophagy is a mechanism that recycles cellular content. It can be triggered when a cell is stressed, or when a cell detects damaged proteins that need to be degraded (Jackson 2015). Autophagy is involved in cell death and interacts with inflammatory systems (Wang et al 2018). SARS-CoV (the 2002 outbreak) and MERS-CoV also interact with autophagy (Fung and Liu 2019).
Like influenza, SARS-CoV-2 infection often results in “cytokine storms”, which are dramatic and damaging increases in levels of chemokine and cytokine proinflammatory molecules, often complicated further by pneumonia (Hayashi et al 2007, Li et al 2012, Wu et al 2012, Dai et al 2013, Brussow et al 2020). Becker 2017 suggestions to mitigate the “cytokine storm”, inflammation, lung injury, and pneumonia were based on in vitro and in vivo research involving clove bud (Syzygium aromaticum) essential oil, eugenol, patchoulol, and trans-cinnamaldehyde (Hayashi et al 2007, Li et al 2012, Wu et al 2012, Dai et al 2013), but there are no studies in humans examining this. It’s important to note that prevention and treatment are not the same thing. An essential oil that kills virus particles in the air or on the skin is a different concept to one that interferes with the actions of a virus once it has entered the body. At this time, we cannot suggest any aromatherapy formulations to either prevent or treat SARS-CoV-2 infection.
Symptom management and psychological wellbeing
Because there is no known cure for COVID-19, medical interventions focus on symptom management, and in severe cases necesitate respiratory support via ventilators. Under no circumstances should you try to address a severe case of the disease, and once shortness of breath occurs, you must seek medical help immediately. If only mild symptoms are present, you could use essential oils to assist in their alleviation – chest rubs containing pinene or cineole rich essential oils such as Eucalyptus (Eucalyptus globulus) or Rosemary (Rosmarinus officinalis), steam inhalation with the same oils, etc. You could also use inhalation to combat the inevitable stress and anxiety. The use of lavender (Lavandula angustifolia) essential oil with citrus essential oils, often sweet orange (Citrus sinensis) or lemon (Citrus limon), has been effective in reducing situational anxiety, as well as chronic anxiety (Lehrner et al 2005, Perry and Perry 2006, Goes et al 2012).
By far the best thing you can do to mitigate the pandemic is to follow the recommendations of the WHO and other public health authorities – social distancing and hand hygiene.
Viruses depend on the host cells that they infect in order to reproduce, and there are several stages to host cell viral infection. SARS-CoV-2 is an enveloped virus, like influenza A virus (IAV) and there is promising in vitro research on some essential oils and how they interfere with the mechanisms used by the IAV to infect cells. However, while some of these “antiviral” mechanisms may possibly translate to SARS-CoV-2, we don’t yet know if the essential oils are clinically effective for influenza, nor do we have a clear idea on route of administration, dosage, safety, delivery systems and so on. And, we do know there are some fundamental differences between IAV and SARS-CoV-2. Therefore, making any assumptions at this point would be a massive stretch. While claims that essential oils will help protect you from, or treat COVID-19 are not based on evidence, this does not mean you cannot or should not make use of essential oils for respiratory and psychological support.
Special thanks to Christine Carson, PhD, Marco Valussi, BSc, and Linda Halcon, PhD for their insightful comments
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