Citronella is the commonly used name for a group of familiar plants best known for insect repelling abilities similar to yarrow.
This herb has such a strong reputation for repelling mosquitoes in particular that a wide variety of products such as live plants, candles, wrist bands, sprays, and tiki torch oils sell like hot cakes to consumers trying to ward off mozzies naturally during warm summer months.
The media induced hysteria surrounding the Zika virus has made these products even more attractive of late. I live in the state of Florida where at least one case of Zika has been confirmed as of this writing. The governor declared a state of emergency regarding the situation with the predictable result of regular pesticide spraying from mosquito fogging trucks out in force around urban neighborhoods.
While repelling mosquitoes seems more important than ever, is citronella really an effective natural strategy for those seeking to avoid bites without the use of neurotoxic DEET and other pesticides? You might be surprised at what I found out!
The Citronella Mosquito Plant Hoax
The picture above shows a potted citronella plant about 2 feet tall that I currently have on my porch. It sits about 5 feet feet away from the seating area and can be easily smelled from that distance.
Marketed as a “mosquito plant” in the United States and Canada, this particular species has a distinctive appearance due to its medium green, lacy leaves. It is a member of the geranium family, Pelargonium citrosum (citrosa), and as such, produces attractive, pleasant smelling blooms in the summer that are pinkish white.
Citronella geranium (citrosa) is claimed to repel mosquitoes within a 10 foot radius due to a continuous fragrant release of oil. However, research has repeatedly failed to back up these claims.
The Journal of the Mosquito Control Association published a study in 1996 that claimed no significant difference between citrosa-treated and nontreated subjects (1).
In another study in the same journal, the citrosa “mosquito plant” was assessed as a wide area repellent against adult, host seeking female mosquitoes (Aedes albopictus and Culex quinquefasciatus). Researchers noted no significant differences in the number of mosquitoes landing on the forearms of human subjects in locations where plants were present compared with areas without plants (2). In fact, the mosquitoes were observed to land and rest on the citrosa leaves directly.
Composition of Citronella Oil
Perhaps the reason the mosquito plant fails to repel mozzies effectively whether you are sitting next to the plant or apply its oils directly is due to the incomplete composition of citronella oil present. Researchers found only about 10% citronellol and 35% geraniol (components of citronella essential oil). Interestingly, the essential oil components from the citronella (citrosa) mosquito plant were found to be 95% identical to commercial rose geranium (3).
The three primary components of citronella oil are citronellol, citronellal, and geraniol. Note that citrosa is completely lacking in citronellal. This is probably why citrosa is not used to make commercial citronella oil.
Hence, if you decide to buy a citronella (mosquito) plant for your porch or patio, buy it because you like the look and fragrance of it, not because you hope to repel mosquitoes!
Will the Real Citronella Please Stand Up!
Before getting discouraged, please realize that there is another side to the citronella story!
There are two other plants that also go by the common name citronella which belong to the lemongrass family.
These perennial clumping grasses Cymbopogon nardus and Cymbopogon winterianus grow to an astonishing size of 6 feet tall and 6 feet wide (2 m). The base stems are magenta-colored while the leaves are long and pointy.
Citronella grass is a favorite to plant in home gardens because it effectively wards off insects such as the destructive whitefly. Thus, it faciliates growing some vegetables without commercial pesticides.
But does it work for mosquitoes?
On the positive side, these two grasses are the species used for the production of commercial citronella oil. Consumers have become familiar with citronella oil in the form of candles, soaps, and natural insect repellent sprays and wrist bands among other products. This oil is also popular and widely used in aromatherapy.
As mentioned earlier, citronella oil contains the following three main ingredients: citronellol, citronellal, and geraniol. Unlike the more popular mosquito plant citrosa, both species of citronella grass contain all three components in the following amounts (4):
- Cymbopogon nardus: up to 20% geraniol. 15% citronellal, and 8% citronellol.
- Cymbopogon winterianus: up to 24% geraniol, 45% citronellal, and 15% citronellol.
Unfortunately, citronella grass in plant form, while effective for pest control when grown in home gardens, isn’t too helpful for repelling mosquitoes when placed on your porch or patio because the amount of insect repelling oils given off by the live plant is very small.
Citronella Oil as a Mosquito Repellent
While the plant itself is not effective for repelling mosquitoes, citronella oil is classified and registered by the Environmental Protection Agency (EPA) as a bio-pesticide, meaning it has an effective and yet non-toxic effect on the human body (5).
The National Pesticide Information Center describes oil of citronella as an effective repellent of insects. It works by masking scents that are attractive to insects, which in turn, makes it more difficult for insects to locate a target.
While citronella oil is classed as a natural insect repellent, research is conflicting as to the effectiveness when used to keep away mosquitoes.
In 2011, the journal Tropical Medicine & International Health published an analysis of 11 studies on the capabilities of citronella oil to repel mosquitoes. Researchers found that when combined with vanillin, the oil did indeed provide protection for up to three hours (6).
However, another study published in the Journal of the Mosquito Control Association reported poor efficacy of 3% citronella candles and 5% incense in protecting subjects from bites of the mosquitoes Aedes aegypti and albopictus. These species are the ones responsible for transmitting diseases such as dengue, chikungunya, Zika, and yellow fever viruses.
The study was conducted under field conditions in a wooded area in Guelph, Ontario. Eight identically dressed subjects were assigned to one of 8 positions on a grid within the study area. Scented candles, incense, unscented candles, or no candles (i.e., nontreated controls) were assigned to 2 positions on the grid each evening. Subjects conducted 5-min biting counts at each position and performed 16 biting counts per evening. Although significantly fewer bites were received by subjects at positions with the scented candles and incense than at nontreated locations, the overall reduction in bites provided by the citronella candles and incense was only 42.3 and 24.2%, respectively (7).
Perhaps the conflicting studies are why the EU has thus far prohibited the commercial use of this oil as an insect repellent under the Biocidal Product Directive 2006.
Does Citronella Work At All?
When I first started researching to write this article, I did not expect the topic to be so conflicting!
It seems that there are a number of myths associated with the use of citronella as a mosquito repellent. The biggest myth is with regard to the “mosquito plant” citrosa. This plant does not repel mosquitoes either in plant or oil form. Don’t be taken in by the false marketing, although it is lovely and smells wonderful if you want to use it for ornamental value only.
Two species within the lemongrass family have a better reputation, and these citronella plants are widely recognized as effective for pest control in a home garden. They are also the source from which commercial citronella oil is made.
While this oil is classed as a natural insect repellent by the EPA in the United States, it is not in the EU. Science is also conflicted with some studies showing protection from mosquitoes and other studies not so much.
Ultimately, it is up to you to determine if citronella provides value to your family. I have found natural insect repellents containing citronella oil to be effective for mosquito protection, but it must be sprayed on liberally and reapplied often (this is the one I use).
In addition, I have found this mosquito bite remedy to be most effective rather than anything herbally based.
What have you found?
Sarah, The Healthy Home Economist
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