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Herb of the Month

by Harold Knoll    

LEMON EUCALYPTUS TREE (Corymbia  citriodora)

Oil of Lemon Eucalyptus is the trade name for the repellent that originated as an extract of the eucalyptus tree, native to Australia. In distilling the essential oil from the leaves of the lemon eucalyptus tree, PMD (para-menthane-3, 8 diol) is left over as a waste product. The refined oil is very different from the unprocessed tree oil. It is this waste product that has been shown to be effective in repelling mosquitoes, more so than the oil itself. Researchers have reported that PMD is the only plant-based repellent that has been advocated for use in disease endemic areas by the Center for Disease Control, due to its proven clinical efficacy to prevent malaria and because it is considered to pose no risk to human health. Although insect repellent products containing Oil of Lemon Eucalyptus are available, an expert cautions against using anything but CDC- and EPA-recommended active ingredients, such as PMD, in areas with disease risk.

Some testing has shown that concentrations of 20-26% PMD may perform as well as 15-20% DEET against both mosquitoes and ticks (Consumer Reports, 2010). PMD’s maximum protection time against mosquitoes and ticks is shorter than DEET’s according to EPA documents.

Most Oil of Lemon Eucalyptus products on the market are made by Spectrum Brands and sold under the brand names Repel and Cutter. These have concentrations of 30% Oil of Lemon Eucalyptus and 20% PMD. The Repel website does not recommend Oil of Lemon Eucalyptus/PMD (naturally derived) when the risk of West Nile virus is high or against sand flies or the biting midges known as no-see-ums. Citronellol and other chemicals in the extract are known allergens. This repellent can irritate the lungs.

Synthetic PMD can be found in some repellent products at a concentration of 10%. These provide only two hours of protection, but present less risk of allergic skin reactions. This product can also irritate the lungs.

DEET is a strong eye irritant, melts some plastic and damages some fabrics. In a few cases, neurological symptoms have been reported. But it is effective against a wide range of pests and is widely used with few serious adverse reactions. The Environmental Working Group (EWG) says this may be the best choice if West Nile virus is a risk. EWG says, “bug-borne diseases should not be taken lightly. Mosquito and tick bites can transmit life-changing illnesses like West Nile Virus and Lyme disease….DEET should be handled with caution. Still, after reviewing the evidence, EWG has concluded that DEET is generally safer than many people assume and remains a viable option for people in areas infested with disease-carrying pests.” For a complete analysis of bug repellents, see EWG’s Guide to Bug Repellents.

Oil of Lemon Eucalyptus/PMD is not appropriate for all situations, but is a good choice for people who want a botanically-based bug repellent. It is much more effective than any other botanically-based repellent.

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