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We all want natural alternatives to harsh chemical repellents, but do any really work? Learn how to make your own repellent with essential oils scientifically shown to be as effective as DEET
Zika virus and it's purported link to microcephaly has become the latest in a long list of mosquito-borne illnesses that are causing people concern. Whether or not you believe in the link between Zika and birth defects, the fact that mosquitoes cause tremendous human suffering is undeniable. Mosquito-borne illnesses kill more than a million people annually. The little blood-suckers transmit maladies from malaria to West Nile virus, Chikungunya, and yellow fever--and even heartworm to our beloved canine companions.
Government health authorities continue recommending DEET (N,N-diethyl-meta-toluamide), which does work in repelling mosquitoes. However, this potentially toxic chemical is not without its own risks, producing effects similar to deadly nerve gases and pesticides.[i]
We want natural alternatives, but do any really work? The science says yes!
A number of essential oils have proven effective for repelling mosquitoes, including the Aedes Aegypti variety--the most notable Zika transmission vector. It isn't surprising that essential oils would be effective because, over the millennia, plants have needed to manufacture "insect repellants" to ensure their survival. Many of the individual chemical compounds in essential oils have insect repelling properties. Any one essential oil may contain hundreds to thousands of compounds--terpenes, alcohols, esters, aldehydes, ketones, phenols, alcohols, esters, and the list goes one.
Modern science is just beginning to sort out which plant-based extracts effectively deter each type of insect. Fortunately, there are a few essential oils that Aedes Aegypti mosquitoes find highly distasteful, and you can use this to your advantage.
Litsea Oil Ranks #1 on Mosquitoes' Most Unwanted List
In an attempt to find safe and ecofriendly plant-based insect repellants, researchers tested 23 essential oils for their mosquito-repelling properties, specifically against Aedes Aegypti. Three essential oils outperformed the rest: litsea, geranium and rosewood oils. The results will be published in the September 2016 issue of Journal of Arthropod-Borne Diseases.[ii]
Litsea oil ranked highest in making the little pests turn their proboscises and head for the hills. Litsea showed outstanding repellency at all three concentrations tested (1, 10 and 100 ppm), comparing favorably to DEET and DEPA (N,N-diethyl phenylacetamide). Litsea oil comes from the fruit of the Litsea cubeba tree, an evergreen native to Japan, southern China and southeast Asia. In this particular study, the top 10 mosquito-repelling essential oils were identified as the following, listed in order of highest effectiveness:
The insect repelling properties of litsea oil are not unique to this study. In 2015, the synergistic effects of the same 10 essential oils were evaluated, in various combinations--again, specifically targeting Ae. Aegypti. [iii] The most effective blends had litsea as one ingredient, especially when combined with lemon scented (lemon eucalyptus) or lemongrass oil. The little bloodsuckers are clearly not lemon fans.
Lemon Eucalyptus, Geranium and Rosewood
"Lemon scented" (Eucalyptius citriodora) oil comes from a large tree whose name was recently changed to Corymbia. Corymbia citriodora is lemon eucalyptus, the oil being derived from the leaves of the lemon eucalyptus tree. "Lemon scented" (lemon eucalyptus) oil is 85 percent citronellol. Just as the name suggests, citronellol is the primary compound in citronella, well known for its insect-repelling properties.
Adding to the botanical confusion, there is a commercial product made from lemon eucalyptus called "oil of lemon eucalyptus," also called PMD, which is CDC-approved by as an insect repellant.[iv] Although it comes from the same plant, this oil is not the same as the essential oil extracted from the Corymbia citriodora leaf, but rather a byproduct of the distillation process.
Another oil containing citronellol is geranium oil. Given its chemical similarities to citronella, it's not surprising it ranked third for mosquito repellency. Geranium oil comes from Pelargonium graveolenes, a shrub native to South Africa, Zimbabwe and Mozambique. It has a pleasing scent ranging from lemon to rose, depending on the age of the leaves. Geranium oil has a number of medicinal benefits, including antifungal.
Ranking second, rosewood oil is extracted from Aniba rosaeodora, an evergreen tree indigenous to Peru and Brazil. Also called "bois-de-rose," it belongs to the Laurel plant family along with camphor, bay, cinnamon and cassia. Rosewood's scent is very pleasant with health benefits reported for pain relief, wound healing, stress reduction and asthma.
Citronella, eucalyptus, geranium, lemon and lemongrass essential oils are also some of the most frequently patented oils for repelling mosquitoes, according to a 2011 Brazilian literature review.
Six Other Skeeter-Beaters
In addition to the above, seven other common essential oils are scientifically shown to have excellent mosquito repelling properties.
2. Catnip: Catnip (Nepeta cataria) essential oil, which contains nepetalactone, was deemed "10 times more effective at repelling mosquitoes than most commercial bug repellants" by Iowa State researchers, including Aedes species.
3. Clove: Clove was determined to be the most effective against Ae. Aegypti mosquitoes of the 38 essential oils tested in this 2005 study. Undiluted clove oil repelled 100 percent of the mosquitoes for two to four hours.
Why Not Try Making Your Own?
The effectiveness of an insect repellent depends not only on its ability to deter the insets but on how long the effect lasts. The main difference between DEET and essential oils (besides toxicity) is the length of time they remain effective once applied to your skin. Many essential oils are quite effective initially, but protection quickly wanes due to their volatility--in other words, they evaporate. Therefore, you have to apply a plant-based repellent more often than a chemical repellent. The insect repelling effects of essential oils last anywhere from a few minutes to a few hours. Commercial manufacturers deal with this by adding various "fixatives" to prolong the benefits, such as vanillin, coconut oil, mustard oil and other agents.
Keep in mind that some essential oils are irritating to the skin if applied full strength, so it's always a good idea to dilute them. If you would like to try your hand at making your own plant-based insect repellent, herbalist Annmarie Gianni has the following suggestions to guide your efforts.
Water-Based Repellent Spray
Into a spray bottle, use four ounces of witch hazel and/or distilled water as a base. Add 10 drops of your main essential oil, along with a few drops of any other desired oils.
An emulsifier is helpful such as aloe vera gel, vinegar or vodka. Vodka also acts as a preservative.
The spray bottle is handy for spraying on your skin, and nicely portable for reapplying often.
For a mosquito-repelling topical oil, mix essential oils into a carrier oil. Suggested carrier oils include non-GMO soybean, sunflower, apricot kernel, coconut, grapeseed, jojoba, almond, olive, or neem oil.
Some oils possess insect repelling properties of their own, such as neem, coconut, soybean, palm and andiroba (Carapa guianensis). Advice varies as to ratios, but Annmarie suggests 40 to 50 drops of essential oil per eight ounces of carrier oil.
Vanillin has been shown to extend the duration of protection. One study found five percent vanillin added to an essential oil blend repelled mosquitoes for six to eight hours, depending on the species.[viii]
As you can see, there are many safe, ecofriendly plant-based alternatives to harsh chemical insect repellents. Try mixing together a few of your favorites--at least those with some science to back them up.
Remember, the best prevention comes from covering your skin with clothing, as well as clearing your yard of stagnant water and potential mosquito breeding camps. Life is too short to lose sleep worrying about getting sick from an insect bite, so this is a great time retrieve those essential oils from your pantry and let your inner "mad scientist" come out and play!
Get more information on Essential Oils on GreenMedInfo.com's research dashboard.
[iii] Uniyal A et al. "Synergistic effect of effective oils against Aedes aegypti female mosquito, vector of dengue and chikungunya" International J Mosquito Research 2015;2(4): 29-35 ISSN: 2348-5906
[iv] "CDC Adopts New Repellent Guidance for Upcoming Mosquito Season" CDC Press Release
[vi] Noosidum A et al. "Excito-repellency properties of essential oils from Melaleuca leucadendron L., Litsea cubeba (Lour.) Persoon, and Litsea salicifolia (Nees) on Aedes aegypti (L.) mosquitoes" J Vector Ecology 2008;33(2): 305-312 doi: https://dx.doi.org/10.3376/1081-1710-33.2.305