If only it were that simple. If all one would have to do to prevent the SARS-CoV-2 virus from infecting the respiratory tract is to inhale some vapour from eucalyptus essential oil, our worries would be over. The eucalyptus oil “remedy” is being circulated in a post that claims “Doctors from the University of Havana Cuba confirmed and demonstrated that the CoronaVirus (COVID -19) does not develop in environments where 1,8 Epoxy -p Methane is used, which is the best known anti-virucidal, antiseptic and bactericidal component of eucalyptus.” The first clue that the science here is questionable is that 1,8 Epoxy-p-Methane is a nonsensical name, as anyone with any chemical background would recognize. The actual compound in eucalyptus essential oil is 1,8-Epoxy-p-Menthane, also known as 1,8-cineol. That missing “n” makes a big difference. Methane and menthane are totally different compounds. But that is hardly the point. The much more significant point is that there is absolutely no evidence that doctors at the University of Havana have carried out any investigation of eucalyptus essential oil in connection with COVID-19. Neither is there any evidence that anyone else has carried out a pertinent study. What is known, though, is that companies selling essential oils have promoted their use for coronavirus infections.
The term “essential” means that the oil contains the essence of the plant’s fragrance, not that it is in any way essential for its existence or for the existence of any other living organism. Essential oils are widely used to produce perfumes and to add scent to cosmetics and cleaning products. They are also used as flavourings in foods and beverages and have been used historically as medical treatments either by ingestion, application to the skin or as “aromatherapy.” Evidence for efficacy as a medical treatment is scarce but marketers have succeeded in making essential oils into a huge business based on anecdotes and “in vitro” studies. Such studies deal with the effects of essential oils on various microbes in a Petri dish.
Eucalyptus essential oil is obtained from the leaves of the Australian Eucalyptus globulus tree, the same leaves that serve as the main diet for koala bears. The oil is a complex mixture of 1,8-cineol (eucalyptol), limonene, α-pinene, γ-terpinene, and α-terpineol, compounds that do have antimicrobial properties. In the laboratory, the oil suppresses the multiplication of the herpes simplex virus and inhibits the activity of the H1N1 influenza virus after a ten-minute exposure. This, though, is a long way from showing any clinical benefits. There are claims that eucalyptus oil vapour acts as a decongestant, and the oil is also a component of some over-the-counter cold and cough remedies although there are no good studies showing any efficacy. Vicks VapoRub is a popular product that contains eucalyptus oil along with menthol and camphor and is promoted as a remedy to relieve cough, nasal congestion and muscle aches and pains due to colds. Again, the evidence is anecdotal. Some people swear that putting Vicks VapoRub on the souls of the feet and covering them with a towel or socks gets rid of a cough overnight. At least this isn’t likely to do any harm. However, promoting eucalyptus essential oil as a preventative or treatment for COVID-19 infections is not harmless because a belief that this can ward off infection may distract from the importance of physical distancing.
The Food and Drug Administration in the US has sent warning letters to companies selling essential oils that “are misleadingly presented as safe or effective for the treatment or prevention of COVID-19.” These claims have now been removed from websites but posts still circulate about the benefits of eucalyptus oil vapours offering protection against viral infection. There is no evidence for this, but that does not mean that a proper controlled trial is not worth pursuing. After all, that is the only way to separate anecdote from reputable science.