Citronella oil is one of the essential oils obtained from the leaves and stems of different species of Cymbopogon (lemongrass). The oil is used extensively as a source of perfumery chemicals such as citronellal, citronellol and geraniol. These chemicals find extensive use in soap, candles and incense, perfumery, cosmetic and flavouring industries throughout the world.
Citronella oil is also a renowned plant-based insect repellent, and has been registered for this use in the United States since 1948. The United States Environmental Protection Agency considers oil of citronella as a biopesticide with a non-toxic mode of action. However, since citronella insect repellant effects were not proven within the EU, the use of citronella as an insecticide is prohibited under the Biocidal Product Directive 2006.
Research also shows that citronella oil has strong antifungal properties, is effective in calming barking dogs,  and has even been used as a successful spray-on deterrent against pets destroying household items.
Citronella oil is classified in trade into two chemotypes:
- CAS: 89998-15-2
- CAS: 8000-29-1
- EINECS: 289-753-6
- FEMA: 2308
- CoE: 39
- Obtained from: Cymbopogon nardus Rendle
- Consists of geraniol (18-20%), limonene (9-11%), methyl isoeugenol (7-11%), citronellol (6-8%), and citronellal (5-15%).
- CAS: 91771-61-8
- CAS: 8000-29-1
- EINECS: 294-954-7
- FEMA: 2308
- CoE: 2046
- Obtained from: Cymbopogon winterianus Jowitt
- Consists of citronellal (32-45%), geraniol (11-13%), geranyl acetate (3-8%), limonene (1-4%).
- The higher proportions of geraniol and citronellal in the Java type make it a better source for perfumery derivatives. The name Cymbopogon winterianus is given to this selected variety to commemorate Mr. Winter—an important oil distiller of Ceylon, who first cultivated and distilled the Maha Pangeri type of citronella in Ceylon.
Both types probably originated from Mana Grass of Sri Lanka, which according to Finnemore (1962) occurs today in two wild forms--Cymbopogon nardus var. linnae (typicus) and C. nardus var. confertiflorus. Neither wild form is known to be used for distillation to any appreciable extent.
Direct application of citronella oil has been found to raise the heart rate of some people. Health Canada is in the process of phasing out citronella entirely, as an insect repellent. The EPA, on the other hand, finds no known toxicity for citronella.
At present, the world production of citronella oil is approximately 4,000 tonnes. The main producers are China and Indonesia - producing 40% of the world's supply. The oil is also produced in Taiwan, Guatemala, Honduras, Brazil, Sri Lanka, India, Argentina, Ecuador, Jamaica, Madagascar, Mexico, and South Africa.
The market for natural citronella oil has been eroded by chemicals synthesised from turpentine derived from conifers. However, natural citronella oil and its derivatives are preferred by the perfume industry.
Use as an insect repellent
Citronella oil is popular as a 'natural' insect repellent. Its mosquito repellent qualities have been verified by research, including effectiveness in repelling Aedes aegypti (dengue fever mosquito). To be continually effective most citronella repellent formulas need to be reapplied to the skin every 30–60 minutes.
The US Environmental Protection Agency states that citronella oil has little or no toxicity when used as a topical insect repellent, with no reports of adverse effects of concern over a 60 year period. Because some products are applied to human skin, EPA requires proper precautionary labeling to help assure safe use. If used according to label instructions in the US, citronella is not expected to pose health risks to people, including children and other sensitive populations. The US Food & Drug Administration consider citronella oil as generally recognized as safe (GRAS).
In Europe, Ceylon type citronella oil is placed on the category 3 list, with some safety concern regarding methyl eugenol. In the UK, E.U. legislation governing insect repellents came into force in September 2006, which banned citronella as an active ingredient in any insect repellent products. This applied to both insect repellent for humans and animals. It can still be sold as a perfume, but must not be sold as an insect repeller.
- Lawless, J., The Illustrated Encyclopedia of Essential Oils, 1995, ISBN 1-85230-661-0
- "U.S. EPA Citronella Factsheet". Retrieved July 20, 2007.
- * EPA citronella reregistration fact sheet
- Kazuhiko NAKAHARA*, Najeeb S. ALZOREKY1 , Tadashi YOSHIHASHI, Huong T. T. NGUYEN2 and Gassinee TRAKOONTIVAKORN, "Chemical Composition and Antifungal Activity of Essential Oil from Cymbopogon nardus (Citronella Grass)", Japan International Research Center for Agricultural Sciences (JIRCAS),(Tsukuba, Ibaraki 305–8686, Japan), JARQ - October 2003 - (Vol. 37 No. 4 )
- PATTNAIK S., SUBRAMANYAM V. R., KOLE C., 2006, "Antibacterial and antifungal activity of ten essential oils in vitro", Microbios, Vol. 86, No. 349, pp237-246 
- Prabuseenivasan S, Jayakumar M, Ignacimuthu S., 2006, "In vitro antibacterial activity of some plant essential oils.", BMC Complement Altern Med." Nov 30;6:39 
- Segelken, Roger (1996). "Study: 'Nuisance-barking' dogs respond best to citronella spray collars". Cornell Chronicle. Retrieved 2009-04-22.
- Chang, Yu Shyun, 2007, 8 Map species from Malaysia for ICS, Forest Research Institute Malaysia, Workshop on NFP, 28–29 May 2007, Nanchang, PR China 
- Online referenced article, Torres, R.C., Tio, BDJ, Citronella oil industry: challenges and breakthroughs 
- FOODNET, The Association for Strengthening Agricultural research in Eastern and Central Africa 
- Baldacchino, F., Tramut, C., Salem, A., Liénard, E., Delétré, E., Franc, M., Martin, T., Duvallet, G. & Jay-Robert, P. 2013: The repellency of lemongrass oil against stable flies, tested using video tracking. Parasite, 20, 21. doi:10.1051/parasite/2013021
- KIM, Jeong-Kyu; Chang-Soo KANG, Jong-Kwon LEE, Young-Ran KIM, Hye-Yun HAN, Hwa Kyung YUN (2005). "Evaluation of Repellency Effect of Two Natural Aroma Mosquito Repellent Compounds, Citronella and Citronellal". Entomological Research 35 (2): 117–120. doi:10.1111/j.1748-5967.2005.tb00146.x.
- Ibrahim Jantan, and Zaridah Mohd. Zaki, Development of environment-friendly insect repellents from the leaf oils of selected Malaysian plants, ASEAN Review of Biodiversity and Environmental Conservation (ARBEC), May 1998.
- Trongtokit Y, Rongsriyan Y, Komalamisra N, Apiwathnasom L, Comparative repellency of 38 essential oils against mosquito bites, Phytother Res. 2005 Apr;19(4):303-9 
- "Test: Mosquito Repellents, The Verdict" Choice, The Australian Consumers Association
- Muncuoglu K.Y., Galun R., Bach U., Miller J., Magdassi S., Repellency of essential oils and their components to the human body louse, Pediculus humanus humanus, Entomologia experimentalis et applicata (Entomol. exp. appl.) ISSN 0013-8703 CODEN ETEAAT, vol. 78, no3, pp. 309-314 (14 ref.), 1996. 
- Mumcuoglu,-K-Y; Magdassi,-S; Miller,-J; Ben-Ishai,-F; Zentner,-G; Helbin,-V; Friger,-M; Kahana,-F; Ingber,-A; Repellency of citronella for head lice: double-blind randomized trial of efficacy and safety, Isr-Med-Assoc-J. 2004 Dec; 6(12): 756-9 
- "U.S. EPA Citronella Factsheet". Retrieved July 16, 2011.
- "Re-evaluation of Citronella Oil and Related Active Compounds for Use as Personal Insect Repellents" (PDF). Responsible Pesticide Use (Pest Management Regulatory Agency (Canada)). 2004-09-17. ISBN 0-662-38012-6.
- "So Then: Who’s Afraid of Citronella Oil? Update!" Cropwatch Newsletter Vol 2,Issue 1, No. 1
- "HSE Biocides Unit responds to The Daily Telegraph article" 13 October 2006