Citronella oil is an essential oil obtained from the leaves and stems of different species of Cymbopogon (lemongrass).

The oil is used extensively as a source of fragrance chemicals such as citronellal, citronellol and geraniol. These chemicals find extensive use in the soap, candle and incense, perfumery, cosmetic and fragrance industries worldwide. Citronella oil is also a plant-based insect repellent and has been registered for this use in the United States since 1948. The United States Environmental Protection Agency considers citronella oil a biopesticide with a non-toxic mode of action.

Citronella oil has strong antifungal properties. Citronella oil from the Cymbopogon species should not be confused with other similar lemon oils from Corymbia citriodora and Pelargonium citrosum.

Health questions
Direct application of citronella oil has been found to increase the heart rate of some people.

Global production
The market for natural citronella oil has been eroded by chemicals made from turpentine derived from conifers. However, natural citronella oil and its derivatives are preferred by the perfume industry.

Use as a repellent
Citronella oil is popular as a natural insect repellent. Its anti-mosquito properties have been verified by research, including its effectiveness in repelling Aedes aegypti (dengue mosquito). To be continuously effective, most citronella repellent formulas must be reapplied to the skin every 30-60 minutes.

Citronella candles (burning citronella oil) are no more effective than other candles at repelling insects, and experts do not recommend it as a useful method.

Research also shows that citronella oil is an effective repellent for body lice, head lice, and flat flies. A study conducted by ARPA in 1963 determined that hydroxycitronellal was an effective repellent for both aquatic and terrestrial leeches.

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. Some products are applied to human skin, so the EPA requires proper precautionary labeling to ensure safe use. When used according to label directions in the US, citronella is not expected to pose a health risk to humans, including children and other sensitive populations.