P-menthane-3,8-diol is a p-menthane monoterpenoid in which p-menthane carries hydroxy groups at C-3 and C-8. P-menthane-3,8-diol derives from a hydride of a p-menthane. p-Menthane-3, 8-diol is found in fruits. p-Menthane-3, 8-diol is a constituent of the roots of Litsea cubeba (mountain pepper). p-Menthane-3, 8-diol, also known as para-menthane-3, 8-diol and PMD, is an active ingredient used in insect repellents. p-Menthane-3, 8-diol smells similar to menthol and acts as a coolant. PMD is found in the oil within leaves of the Eucalyptus citriodora tree. This tree is native to Australia, but is now cultivated in many warm places around the world. This oil, when refined for use in insect repellents, is known as Oil of Lemon Eucalyptus or, more commonly, Citriodiol.

Typically, Citriodiol contains 64% PMD (a mixture of the cis and trans isomers of p-menthane-3, 8-diol). Citriodiol has been notified under the European Biocidal Products Directive (BPD) 98/8/EC and is currently proceeding through the registration process with the Heath and Safety Executive in the UK. p-Menthane-3, 8-diol is the only natural ingredient that can now be used as an insect repellent^[1-3].

Fig 1. Chemical structure formula and three-dimensional structure of p-Menthane-3,8-diol

P-menthane-3,8-diol is used to make products that are applied to human skin and clothing for the purpose of repelling insects, such as mosquitoes, biting flies and gnats. P-menthane-3,8-diol can be used in two types of consumer pesticide products: a spray and a lotion. When used according to the label guiding, P-menthane-3,8-diol products are not expected to cause harm to humans or the environment.

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 p-Menthane-3,8-diol, and the exact composition is rarely specified and is commonly assumed to be a complex mixture.

p-Menthane-3,8-diol 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 p-Menthane-3,8-diol 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 p-Menthane-3,8-diol products are not made from E. citriodora oil, but rather from synthetic citronellal.

Refined OLE contains approximately 64% p-Menthane-3,8-diol (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 "p-Menthane-3,8-diol 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 "p-Menthane-3,8-diol and related oil of lemon eucalyptus compounds". 

p-Menthane-3,8-diol can be synthetically manufactured from materials derived from natural sources. E. citriodora oil contains only 1-2% p-Menthane-3,8-diol and is therefore different from OLE as registered with the EPA which has a minimum 64% p-Menthane-3,8-diol. p-Menthane-3,8-diol is as effective as DEET when used in like quantities. 

References

[1]M. Debboun, S. Frances, D. Strickman. History of insect repellents. Insect repellents–principles, methods, and uses. (1st Ed.), CRC press, Fort Lauderdale (2006).
[2]C. Costantini, A. Badolo, E. Ilboudo-Sanogo.Trans. R. Soc. Trop. Med. Hyg, 98 (2004), p. 644.
[3]J.K. Trigg. J. Am. Mosq. Control Assoc, 12 (1996), p. 243.