Oil of Lemon Eucalyptus (OLE)

Lemon Eucalyptus is not – I repeat NOT – the same as Lemon-Eucalyptus or Lemon & Eucalyptus. The Lemon Eucalyptus (Corymbia citriodora) is a tall tree that grows up to 35 meters tall and is endemic in temperate and tropical north eastern Australia. The species is now cultivated in many warm places around the world.
The narrow leaves smells strongly of lemons. The lemon eucalyptus is closely relatied to the eucalyptus (Eucalyptus globulus), but lacks the specific smell of that genus. The essential oil of the tree consists mainly of citronelal (80%). This compound does have insect repellent properties and research shows high repellent effectiveness against mosquitoes[1].

But it is the remaining 20% that is highly interesting: it is chemically known as p-Menthane-3,8-diol, para-menthane-3,8-diol, menthoglycol or PMD. When refined to increase its PMD, it is known in the United States as oil of lemon eucalyptus (OLE) or by the tradenames Citrepel and Citriodiol. Refined OLE contains approximately up to 70% PMD (a mixture of the cis and trans isomers of p-menthane-3,8-diol).

OLE is an active ingredient used in insect repellents. It smells similar to menthol and has a cooling feel. OLE is in all likelyhood a more potent mosquito repellant than DEET[2]. Did I already mention that mosquitoes are increasingly 'insensitive' to DEET[3]?

[1] Kim et al: Evaluation of Repellency Effect of Two Natural Aroma Mosquito Repellent Compounds, Citronella and Citronellal in Entomological Research – 2005 
[2] Carroll, Loye: PMD, a Registered Botanical Mosquito Repellent with Deet-Like Efficacy in Journal of the American Mosquito Control Association - 2006
[3] Stanczyk et al: Behavioral insensitivity to DEET in Aedes aegypti is a genetically determined trait residing in changes in sensillum function in PNAS - 2010.

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