Citronella oil, a widely recognized plant-based insect repellent, is derived from the steam distillation of the leaves and stems of specific Cymbopogon grasses, such as C. nardus or C. winterianus. Valued for its mild, citrus-like scent, the oil has a long history of use in traditional medicine and perfumery, but its most popular application today is the deterrence of biting pests. Its reputation as a gentle alternative to synthetic chemicals makes it a popular choice for natural pest control.
The Specific Insects Citronella Repels
Citronella’s primary effectiveness is directed toward mosquitoes, particularly those species responsible for transmitting diseases. Studies confirm its repellent action against Aedes aegypti (which carries dengue and Zika) and various Culex species (which transmit West Nile virus). Topical application offers short-term protection, though effectiveness often requires higher concentrations or more frequent reapplication compared to synthetic repellents. A concentration as low as 3% has been shown to be effective against Aedes aegypti.
The oil also demonstrates moderate efficacy against other flying insects. This includes non-biting and biting flies, such as houseflies and stable flies, which are repelled by the oil’s strong, masking scent. Citronella can also deter gnats and biting midges, sometimes called “no-see-ums,” reducing their presence in outdoor spaces. Additionally, the oil has been observed to repel body lice and head lice, and in some formulations, it shows limited activity against certain species of ants and ticks.
How Citronella Achieves Repellency
The insect-repelling properties of citronella oil come from a blend of volatile organic compounds released into the air upon application. The three primary chemical components responsible for this action are citronellal, geraniol, and citronellol, all types of monoterpenes. The Java type of citronella oil, derived from Cymbopogon winterianus, is considered superior because it contains higher proportions of citronellal and a greater total percentage of these active compounds.
The mechanism of repellency is largely understood as “olfactory masking,” where the strong scent of the oil overwhelms an insect’s sensory system. Mosquitoes locate a host by detecting carbon dioxide and lactic acid emanating from the skin. Citronella’s intense fragrance confuses the insect’s chemoreceptors, making it difficult for them to track host odors. This interference prevents the insect from landing and feeding, effectively deterring them from the treated area.
Factors Affecting Efficacy and Target Limitations
A primary limitation of citronella-based products is the high volatility of its active compounds, causing them to evaporate quickly once exposed to air or applied to the skin. This rapid dissipation drastically limits the duration of effectiveness. Many topical applications provide complete protection for less than two hours, sometimes as short as ten minutes, which is significantly less than synthetic repellents.
The efficacy of citronella is also highly dependent on the product formulation. Citronella candles, for example, are far less effective than topical sprays or lotions because the active oil is dispersed widely rather than concentrated near the person. Furthermore, citronella is not a universal repellent and is ineffective against stinging insects like bees and wasps, as well as household pests such as cockroaches.