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Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Insights on Insect Repellents

By Paul S. Auerbach, MD | Published Aug 24, 2006

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photo of Scott Carroll by Jenella Loye

At Tropical Medicine 101, we had a wonderful lecture about insect repellents from Dr. Scott Carroll, a biologist from the University of California, Davis who studies insect behavior and evolution. One of the more interesting points he made is the fact that "lemon eucalyptus," which is marketed as a repellent and felt to be as effective as 7.5% DEET, is actually not from eucalyptus, but is actually a product from the lemon-scented gum tree Corymbia citriodora (pictured here).

The product is water-distilled from the leaves, and the repellent is found in the spent fraction as para-menthane-3,8-diol (PMD). Of particular note, true eucalyptus oil does not work as an insect repellent.

Other repellents that are effective contain DEET, or N, N-diethyl-m-toluamide, which is the active ingredient that is most widely used in commercially available insect repellents. A concentration of 20 to 30% is sufficient. Picaridin (KBR 3023 or Bayrepel), also in a 20% concentration, is an excellent repellent, as is 20% IR 3535 (sold as Avon Skin So Soft BUG GUARD PLUS IR3535® EXPEDITION™ Insect Repellent Aerosol). Picaridin and IR 3535 (ethyl butylacetylaminopropionate) may have more favorable safety profiles compared to DEET, but all three are still highly recommended.