essential oils in the classroom: a rose (or other flowers) would smell as sweet

A story about essential oils being used in classrooms hit the headlines this week. It described how an Auckland primary school had put diffusers into 20 classrooms, using oil blends that would supposedly “stop the spread of viruses and keep children focused at school.” A parent subsequently used the threat of a legal injunction to stop this practice, at least for the moment.

Now, some of the skills children are supposed to gain at school are those used in critical thinking. It would be nice to see the school management applying the same skills to decisions like this¹. I mean, is there actually good evidence that these products actually do what’s claimed for them? Do they “stop the spread of viruses” or “keep children focused at school”? (Trialling them in one classroom & relying on the teacher’s observations is not sufficient, given how susceptible the latter is to confirmation bias.)

There’s certainly a lot of woo claimed for the oils! One of my first hits was this one, which is basically an advertorial and appears to be written by a teacher who has definitely not applied critical thinking skills to the claims they are making. I can safely say this because (among other things) they state that using an essential oil diffuser will increase the oxygen levels in the classroom!!! (I did comment there; who knows how long that will last?)

Searching PubMed using the string <essential+oils+viruses> yields just 195 results. (Replacing ‘viruses’ with ‘rhinoviruses’ – the ones that cause colds – returned precisely zero hits.) The studies listed on the first page are largely in vitro studies (ie looking at the effect of the oils on cells in petri dishes), plus some looking at the value of the oils as surface sanitisers. The papers that come up on a Google Scholar search are the same; they look at cytotoxicity in vitro, on surfaces, & (sometimes) in animal studies -[EDIT] influenza is an example. Yes, these products will definitely kill pathogens in the petri dish & on hard surfaces – most essential oils are strongly cytotoxic². It’s a big leap from there to claim that airborne oil particles will kill viruses and bacteria in the classroom.

Of course, the other question that should have been asked before the oils were used in the classroom was, do they have any documented negative impacts on health? A subsequent Herald article was based on feedback from neurologist Gareth Parry, who noted that “eucalyptus oil and rosemary oil were just two of 11 esstential oils that potentially caused seizures.” There’s been research on this for quite some time (though not by the company providing the oils; not that I could see on their website, anyway) and it goes back a long way – see here & here, for a couple of those earlier studies. (Yes, these document topical &/or internal use, not airborne.)

However, more recent studies are also not exactly promising. This paper looks at the levels of the oils’ active components when evaporated (not diffused³), their concentrations in the room’s air were measured, & their antimicrobial activity assessed. The researchers found that

The anti-microbial activity on airborne microbes, an effect claimed by the use of many essential oils, could only be found at the first 30–60 min after the evaporation began as the highest levels of volatile components in these essential oils appeared to emit into the air…

They documented high emissions of a class of compounds called terpense, and commented that these

warranted … further examination for their health implications, especially for their potential contribution to the increasing indoor levels of secondary pollutants such as formaldehyde and secondary organic aerosols (SOAs) in the presence of ozone.

Not exactly a strong endorsement, then.

Finally, the oils used by the Auckland school were supplied by the company doTERRA, described in the Herald article as a multi-level marketing company, and the fact that the school intended to have “an information evening about the product” was a bit of a red flag to me. Perhaps I’m a cynic, but I wonder if a sales push would have been a part of this. Interestingly, while doTerra’s website strongly implies that these oils will have a positive impact on the health & focus/alertness of teachers and students, it also carries the (small print) disclaimer that (my emphasis)

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.


¹ Actually, I’d ask the same of the Ministry of Education, since in the Herald article, the school principal states that they received clearance from the Ministry to use the oils & diffusers.

² lots of things kill cells in petri dishes

³ since of oil’s components into the air is slower when diffused, I did wonder how likely it would be that any biologically-active concentrations would be achieved at all by a classroom diffuser.

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