P-Menthane-3,8-diol

"p"-Menthane-3,8-diol, also known as "para"-menthane-3,8-diol and PMD, is an active ingredient used in insect repellents. It smells similar to menthol and acts as a coolant [ [http://www.leffingwell.com/cooler_than_menthol.htm Cool without menthol & cooler than menthol and cooling compounds as insect repellents] ] . PMD is found in the oil within leaves of the "Eucalyptus citriodora" tree. These trees grow in Brazil, among other places. This oil, when refined for use in insect repellents, is known as Oil of Lemon Eucalyptus. The Center for Disease Control has recognized PMD as the only effective, natural substance for deterring mosquitoes carrying West Nile Virus. PMD can be synthetically manufactured; however, one study has found that repellents containing synthetic PMD are not as effective as those containing naturally derived PMD (Oil of Lemon Eucalyptus). [Journal of the American Mosquito Control Association:22(3):507-13, 2006.] This study also shows that naturally-derived PMD is as effective as DEET when used in like quantities.

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