This article is part of a column rumor detectorClick here for other texts.
The origin of the rumor
Citronella oil is a common ingredient in mosquito repellents, ones that are meant to prevent biting insects from landing on your skin, without killing them. This effect is partly explained by the strong smell of the product, which disrupts the chemical receptors of mosquitoes, thereby “disguising” your presence.
Right from wrong
From this, some have concluded that a lemon plant would be aromatic enough to keep mosquitoes away from your yard. However, there are no studies to support the claim regarding the plant.
Instead, studies have focused on citronella in essential oil form and its components, including citronellal, citronellol, and geraniol.
And most of these studies have limitations: They were conducted in a lab, where the user does not sweat. However, sweat enhances the evaporation of the oil, which reduces the duration of its effectiveness.
Volunteers are usually covered with essential oil or insect repellent that contains it, and then exposed to one or more species of insects, while researchers assess how many of these insects keep their distance.
The duration of citronella oil’s repellent action appears to depend on the type of plant it is taken from, the concentration used and the mosquito species. So Review of 11 studies published in 2011 It reveals that lemongrass repellent only protects against mosquitoes for about two hours. During this period, they grow up again 95% of mosquitoes are of three types : Aedes aegyptiAnd Anopheles disease And Culex quinquefasciatus, according to the authors of one of these eleven studies.
The literature review also concluded that by combining lemongrass oil with vanillin (5%), it would be possible to repel these three types of mosquitoes for up to 8 hours, under laboratory conditions. Protection time similar to DEET (N,N-diethyl-m-toluamide), the most commonly used synthetic substance in mosquito repellents. However, this estimate has remained inconclusive due to a limited number of studies.
In 2019, new Systematic review of 62 . studies This time he concluded that lemongrass oil has a 100% repellent effect, but against different types than the previous ones: Anopheles culicifacies This is for 11 hours. And they can back off Anopheles Stephensi And Anopheles disease for 8 and 6 hours, respectively, under laboratory conditions. This indicates that the effect can vary greatly, depending on the type of mosquito being targeted. For example, 0.1ml of lemongrass essential oil was kept at bay Anopheles minimus And Anopheles disease For a little over two hours and a little under an hour straight. The percentage of citronella repels in other studies was 52–85%, depending on the concentration of the extracts and the species of mosquitoes.
In addition to offering variable potency, several of these laboratory studies indicate that lemongrass oil is unstable in the presence of air and at high temperatures, which limits its practical applications.
Field work seems to confirm this. One of them, in 2013, Comparing the effectiveness of seven types of commercial mosquito repellents, concluded that bracelets made of lemongrass do not provide significant protection against the attacks of two types of mosquitoes (Aedes albino And Colex Babies). In 1996, a small field study It was found (included only eight people) that exposure to candles and lemongrass gum reduced mosquito bites by 40% and 24%, respectively.
All of this explains why mosquito repellents containing citronella are not recommended for those who travel to endemic areas, for example where insects that can transmit malaria are common. The Quebec Department of Health and Social Services advises against them for those who need long-term protection, as well as for children under the age of two, due to the short duration of their employment.
Rule
So many studies seem to confirm the efficacy of lemongrass oil, but most of them have been done in a lab, which limits their scope. However, in the case of sufficient concentration, there is a tendency to agree that lemon oil will have a repellent effect on certain types of mosquitoes for about two hours if applied to the skin.
Photo: Aedes albopictus having lunch. Source: Fotoshop Tofs / Pixabay
