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Mosquito repellents: ‘Lemon Eucalyptus Oil’ is not ‘Oil of Lemon Eucalyptus’!

There is considerable confusion between ‘lemon eucalyptus essential oil’ and ‘oil of lemon eucalyptus’. Both are used as mosquito repellents but they have quite different chemical compositions and efficacy.

Lemon eucalyptus essential oil (sometimes simply called Lemon eucalyptus oil) is made by steam distilling the dried leaves and twigs of the lemon eucalyptus tree (Eucalyptus citriodora or Corymbia citriodora).  A typical chemical profile for this essential oil is: citronellal (70-90%), citronellol (4-12%), and isopulegol (1-16%).

It also contains small quantities (trace -2%) of p-menthane 3,8-diol (PMD).  PMD is a highly effective and long acting mosquito repellent but because it is only present in such small quantities in lemon eucalyptus essential oil the repellent properties of this essential oil are mainly due to its other components. Unfortunately these other components are relatively volatile and consequently the essential oil only has a short duration of action, typically less than an hour by arm-in-cage test. This is too short a time for it to be a reliable, convenient and effective repellent.

Lemon eucalyptus essential oil also has poor repellency against the aggressive aedes aegypti mosquito, a vector for many illnesses including zika fever, dengue fever, chikungunya and yellow fever. Due to its lack of efficacy lemon eucalyptus essential oil is not approved for use in countries with disease carrying mosquitoes.

It is however possible to process and purify lemon eucalyptus essential oil to reduce the citronellal content while increasing the PMD content. The process involves converting some of the citronellal into PMD, mirroring the natural conversion that occurs in the leaves of the lemon eucalyptus tree. This refined oil, with a minimum of 64% PMD, is commonly referred to as ‘oil of lemon eucalyptus’ (OLE).  

In a nutshell, lemon eucalyptus essential oil is mainly citronellal with a small variable amount of PMD and is not approved for use in disease endemic areas due to its lack of efficacy.  In contrast ‘oil of lemon eucalyptus’ is mainly PMD, which provides highly effective mosquito protection, and is approved for use in all disease endemic areas.

Unfortunately people often confuse these two quite distinct products. For example, journalists often report ‘oil of lemon eucalyptus’ studies as showing the efficacy of lemon eucalyptus essential oil.  Even some aromatherapists, who should know better, perpetuate this confusion by recommending lemon eucalyptus essential oil as a mosquito repellent for protection against the zika virus. It is not approved for this purpose for good reason.

Here at Hebe Botanicals we refine our 'oil of lemon eucalyptus' until it is pure PMD.   This ensures that SAFE has maximum effectiveness and that it is also entirely free of citronellal (hence very little smell).  PMD is the only only plant-based active ingredient effective enough to be approved by the Centres for Disease Control (CDC) for use in disease endemic areas.

SAFE repellent has been independently tested (Study code 13/378) against the aedes aegypti mosquito and was found to be “highly effective”, providing over 6 hours complete protection from landings.  In this comparative arm-in-cage test it outperformed Repel tropical strength repellent which contains two synthetic repellents (30% deet and 3.75% IR3535).

If you are thinking of purchasing lemon eucalyptus essential oil, or any other essential oil, for mosquito protection ask for an independent study demonstrating its effectiveness (the arm-in-cage complete protection time gold standard).  Be prepared to be disappointed.

Dr Steve Humphries


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