Mythbusting: Lemon Eucalyptus Essential Oil as a Mosquito Repellent

It’s now well into the season of spring–almost summer– and once again, we’re dealing with the emergence of pesky insects. Two of the most bothersome bugs found in the United States are the mosquito and the tick. Today’s blog focuses on the mosquito, and ticks will be discussed in an upcoming series, the first of which will be published on the Tisserand Institute.

Mosquitos are one of the world’s leading causes of disease and death. The World Health Organization says about mosquitoes “…their ability to carry and spread disease to humans causes millions of deaths every year. In 2015 malaria alone caused 438,000 deaths” [1]. While malaria is a serious health concern worldwide, it’s not the only mosquito-borne disease that can cause debilitating illness. Others include dengue fever, chikungunya, yellow fever, West Nile virus, Zika, and Eastern Equine Encephalitis [Ibid]. However, for the majority of people in the U.S. mosquitos are an annoyance and nothing more.

When discussing the subject of naturally-derived mosquito repellents, a 2011 article which appeared on the ‘green’ website treehugger.com caused confusion in aromatherapy circles, which continues today. The article’s headline declared that the U.S. Centers for Disease Control (CDC) confirmed lemon eucalyptus oil to be just as effective a mosquito repellent as the commercial repellent DEET [2]. This has led to repeated questions on aromatherapy sites where people ask “how do I make a mosquito spray using lemon eucalyptus oil?”

I admit that I was pretty excited when the article first came to my attention. That excitement rapidly deflated when it became clear the CDC wasn’t talking about lemon eucalyptus essential oil. Instead, the product they were referring to was oil of lemon eucalyptus.

I can hear you thinking “Wait a minute, that’s confusing. They’re *not* the same thing?” Definitely not!

Oil of lemon eucalyptus contains a substance called para-Menthane-3,8-diol (PMD), a naturally occurring compound obtained from the spent distillation of leaves of the Corymbia citriodora  tree (also known as Eucalyptus citriodora or lemon eucalyptus tree). PMD is also synthesized in the laboratory [3].

A 2011 article from Malaria Journal stated that “PMD is the only plant-based repellent that has been advocated for use in disease endemic areas by the CDC due to its proven clinical efficacy to prevent malaria and is considered to pose no risk to human health. It should be noted that the essential oil of lemon eucalyptus does not have EPA (Environmental Protection Agency) registration for use as an insect repellent” [4, italics mine].

Oil of lemon eucalyptus (PMD) has been included in clinical studies [3,5,6,7] and has been registered by the EPA as an effective plant based mosquito repellent, whereas lemon eucalyptus essential oil has not. Though they may be derived from the same source, the two are separate, distinct products.

“Well, dang it!  I just bought a bottle of lemon eucalyptus essential oil to use in a mosquito spray… can I just go ahead and use it anyway, like I’ve seen on some essential oil blogs?”  You *could*….but your homemade product wouldn’t yield the same effect as a commercial product containing oil of lemon eucalyptus. Why not?

One of the primary limitations of using essential oils as insect repellents is their volatile nature; that is, they tend to evaporate quickly and need to be reapplied frequently [Ibid,4].  Also, in an oil of lemon eucalyptus formulation the level of PMD is standardized. Many commercially available PMD repellents contain a level of 30% oil of lemon eucalyptus, containing 65% PMD [Ibid,4].  Lemon eucalyptus essential oil has a very high concentration of the aldehyde citronellal [8, pg.335]; using it at anywhere near the same concentration as oil of lemon eucalyptus would very likely cause skin concerns (or worse). Tisserand and Young, authors of Essential Oil Safety, 2nd edition state regarding aldehydes, “[t]hey often cause skin irritation and allergic reactions”[Ibid, pg 18].

So if you prefer using a naturally derived insect repellent product when mosquitoes arrive at your garden party, you can ‘disinvite’ them by using a product containing PMD. While you certainly can still use lemon eucalyptus essential oil as part of a homemade insect blend, you cannot expect the same level of protection as a product containing oil of lemon eucalyptus.

(Author’s note:  PMD-containing product safety sheets warn that they are not to be used on children under the age of three [10].)

 

References:

1. Mosquito-borne diseases. World Health Organization website, http://www.who.int/neglected_diseases/vector_ecology/mosquito-borne-diseases/en/ accessed May 8, 2017.
2. Novak, S. “CDC confirms lemon eucalyptus oil as effective as DEET”. From www.treehugger.com/lawn-garden/cdc-confirms-lemon-eucalyptus-oil-as-effective-as-deet.html; accessed May 8, 2017.
3. Carroll SP and Loye J. PMD, a registered botanical mosquito repellent with deet-like efficacy. J Am Mosq Control Assoc 2006 Sep;22(3):507-14.
4. Maia M and Moore S.  Plant-based insect repellents: a review of their efficacy, development and testing. Malaria Journal 2011;10(Suppl 1): S11.
5. Frances SP, Rigby LM and Chow WK. Comparative Laboratory and Field Evaluation of  Repellent Formulations Containing Deet and Lemon Eucalyptus Oil Against Mosquitoes in Queensland, Australia.  J Am Mosq Control Assoc, 2014; 30(1):65-67.  
6. Barasa SS, Ndiege IO et al. Repellent activities of stereoisomers of p-menthane-3,8-diols against Anopheles gambiae (Diptera: Culicidae) J Med Entomol. 2002;39:736–741.
7. Trigg JK and Hill N. Laboratory Evaluation of a Eucalyptus-based Repellent against Four Biting Arthropods. Phytother Res. 1996;10(4):313–6.
8. Tisserand R and Young R. Essential Oil Safety, 2nd edition. Churchill Livingstone Elsevier, 2014, Pg 335.
9. Ibid, pg. 18.
10. Nasci R, Wirtz R and Brogdon W.  Protection against Mosquitoes, Ticks, & Other Arthropods.https://wwwnc.cdc.gov/travel/yellowbook/2016/the-pre-travel-consultation/protection-against-mosquitoes-ticks-other-arthropods, accessed May 11, 2017.