p-Menthane-3,8-diol, also known as para-menthane-3,8-diol, PMD, or menthoglycol, is an active ingredient used in insect repellents. It smells similar to menthol and has a cooling feel. There are eight possible isomers of PMD, and the exact composition is rarely specified and is commonly assumed to be a complex mixture. PMD is found in small quantities in the essential oil from the leaves of Eucalyptus citriodora. This tree is native to Australia, but is now cultivated in many warm places around the world. E. citriodora oil, when refined to increase its PMD content for use in insect repellents, is known in the United States as oil of lemon eucalyptus (OLE) or by the tradename Citriodiol. Some commercial PMD products are not made from E. citriodora oil, but rather from synthetic citronellal. Refined OLE contains approximately 64% PMD (a mixture of the cis and trans isomers of p-menthane-3,8-diol). OLE has been notified under the European Biocidal Products Directive (BPD) 98/8/EC (now BPR Regulation (EU) No. 528/212) under its generic name "PMD rich botanic oil" and is currently proceeding through the registration process with the Health and Safety Executive in the UK. It is also registered with Canada's Pest Management Regulatory Agency under the generic name "PMD and related oil of lemon eucalyptus compounds". It is the only natural active ingredient that is permitted to be used an insect repellent in the United States and Europe. PMD can be synthetically manufactured from materials derived from natural sources. This 2011 study also shows that E. citriodora oil contains only 1-2% PMD and is therefore different from OLE as registered with the EPA which has a minimum 64% PMD. A 2006 study showed that PMD is as effective as DEET when used in like quantities.