Why Essential Oils Make Terrible Bug Repellents

We get it: Essential-oil bug repellents sound great. Who wouldn’t want to use a natural plant oil to keep bugs away? But after digging into the research and talking to two mosquito experts, we put essential-oil repellents firmly in the “do not buy” category. Simply speaking, there’s just no way to know how effective they are or for how long. In relying on them, you’re likely heading outdoors with a false sense of security that could put you at greater risk than if you were using nothing at all.

In light of diseases such as Zika and Lyme, the consequences of an ineffective repellent can be dire, so you need one you can trust. A repellent’s trustworthiness starts with EPA approval—a requirement that proves the repellent has been thoroughly tested to confirm that it’s safe and that it performs according to the specifics from the manufacturer. Essential oils have no such standardized oversight, so you’re basically on your own.

Why you should trust us

To learn more about the specifics of mosquito repellency, we spoke to Laurence Zwiebel, a professor of biological science and pharmacology at Vanderbilt University. Zwiebel has been studying insect behavior for almost 40 years, focusing on mosquitoes for the past 25, and specifically looking at how olfaction—the sense of smell—drives mosquito behavior.

We also corresponded with Leslie Vosshall, professor of neurobiology at The Rockefeller University. Vosshall has been studying insects for 30 years, with a focus on mosquitoes and repellency for the past 15 years.

I’ve researched and written guides to bug repellents, mosquito control gear, fly swatters, and ant control. Through that process I’ve spent at least 300 hours analyzing products, testing bug gear, reading dense studies on repellent and pesticide efficacy, and interviewing academics, manufacturers, and scientists at the EPA.

What are essential oils?

Essential oils are chemicals extracted from plants that are, according to the EPA (PDF), “responsible for the distinctive odor or flavor of the plant they come from.” You can think of them as the distilled essence of the plant. Studies into plant-based bug repellents, such as this summary from a 2011 edition of Malaria Journal, have shown that some of these oils can repel insects to varying degrees. Those most closely associated with repellency are citronella oil, eucalyptus oil, and catnip oil, but others include clove oil, patchouli, peppermint, and geranium. According to one analysis, “More than 3,000 EOs [essential oils] from various plants have been analyzed thus far, and approximately 10% of them are commercially available as potential repellents and insecticides.” The formulas we found are typically a mixture of multiple oils at very low concentrations, rarely above 3 or 4 percent each, mixed with water or other inert ingredients.

Why essential oils’ lack of EPA oversight matters

Any insect repellent containing DEET or picaridin must undergo extensive, consistent testing under the EPA's product-performance test guidelines, the result of which is a legally binding label on the bottle. That label includes the ingredients, the time of protection, toxicity information, and specific instructions on use and disposal. The tests give you a clear understanding of the repellent, as well as an underlying assurance that it’s safe for use on adults, children, or animals. The EPA categorizes essential oils as a “minimum risk pesticide,” so they don’t undergo this testing. Without it, you can’t confirm what’s in the bottle, whether it’s safe for use, or how effective it is. This also leaves the door open for misleading marketing claims. As Zwiebel told us, “I am very concerned about the lack of regulatory oversight and the ability to disinform or in some cases completely misinform consumers. There is a lot of mayhem out there in the field.”

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The extent of the EPA’s involvement in essential-oil repellents is minimal. The agency requires that manufacturers list the ingredients and their concentration levels, that there be no misleading statements on the bottle, and that the repellent “may not bear claims to control rodent, insect or microbial pests in a way that links the pests with any specific disease.” In other words, an essential-oils label can say that the substance repels mosquitoes and ticks, but they can’t say it will protect you from Lyme, Zika, or any other vector-borne disease. EPA-approved repellents, such as those containing picaridin or DEET, can clearly state that they offer protection from those diseases. Big difference there.

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One thing very few essential-oil labels indicate is how long the repellency will last—a crucial piece of information if your goal is to protect yourself from disease-ridden insects. Even armed with a knowledge of essential oils and an understanding of their concentration within a repellent, there’s still no way to know what kind of protection you might be getting (or if you’re getting any at all). Zwiebel explained, “These essential oils can be more or less effective depending on how they’re prepared, how pure or not pure they are.” He continued, “You really don’t know what you’re buying.”

With minimal EPA oversight, essential-oil labeling lacks a guarantee of accuracy or independent verification, which can lead to misleading claims, missing information, and inconsistency. Photo: Doug Mahoney

To be fair to essential-oil manufacturers, there’s no clear process for them to earn the EPA’s badge of legitimacy as a bug repellent. These oils aren’t classified as pesticides, so they don’t merit testing under the EPA’s protocols, which are the single standard that judges repellency against disease vectors. Ironically, a big part of the appeal of essential oils—their relative safety—is exactly what excludes them from joining the big leagues of the EPA-approved repellents, and that’s unlikely to change until the EPA revises its own standards. In the meantime, we can only go on the science available, and that research leads most experts to dismiss oils as unsafe bug repellents for the same reason we discourage people from using them: uncertainty.

Because there’s no idea how effective an essential-oil repellent is, they offer little more than a placebo of security, and that can have severe consequences. Vosshall explained, “People think they are being protected from biting insects and ticks with these products and they are not protected.” She continued, “If these people are in areas where ticks are spreading Lyme and other related pathogens and mosquitoes are spreading Zika, malaria, dengue, yellow fever, west nile, and chikungunya they have the potential to be bitten and infected.” She told us that under no circumstances would she ever recommend an essential-oil repellent. Zwiebel also has little confidence in their effectiveness: “I certainly don’t buy any of those products,” he told us. An article in The New England Journal of Medicine, in a similar conclusion, notes, “Alternative ‘natural’ products generally fail to live up to their reputations for greater safety and effectiveness and offer their users a false sense of security.” Last, the Centers for Disease Control and Prevention recommends picaridin, DEET, or another EPA-regulated repellent. No essential-oil repellents make the CDC’s list. (Oil of lemon eucalyptus is a plant-based EPA-approved repellent but is not an essential oil, a distinction that both the CDC and the repellent summary from the Malaria Journal make.)

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Regulations aside, they don’t work that well

Even if essential oils were subject to the EPA’s efficacy-testing guidelines, all indications are that they would fall short of repellents containing picaridin and DEET. Essential oils are just not that great at repelling mosquitoes and ticks.

A major problem is the fact that essential oils are very volatile, meaning they evaporate quickly. In 2002, researchers tested seven essential-oil repellents against DEET, publishing the results in The New England Journal of Medicine. Aside from a soybean-based repellent that offered 95 minutes of protection, “all other botanical repellents we tested provided protection for a mean duration of less than 20 minutes.” A 2005 study published in the journal Phytotherapy Research compared the repellency of 38 essential oils and found that none of them, even when applied at the very high concentrations of 10 percent and 50 percent, prevented mosquito bites for up to two hours. (You can expect even less of the repellents we looked at, which had multiple oils with a concentration of roughly 1 to 4 percent.) Another study, this one published in BioMed Research International, states that “insect repellents with citronella oil as the major component need to be reapplied every 20–60 minutes.”

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And even when freshly applied, they’re not as strong as picaridin or DEET. Zwiebel, the olfactory expert, explained that a mosquito interprets the world through multiple, sometimes hundreds, of chemical receptors. He likened these receptors to the giant cluster of microphones facing a politician at a podium. The majority of these receptors are tuned to odors, but others sense taste, heat, and humidity. Depending on the species, there can be a lot of them, “hundreds, in some cases.” According to Zwiebel, Anopheles gambiae, the mosquito that carries malaria, has “79 odor receptors, 34 ionotropic receptors, a host of gustatory receptors, heat receptors, humidity receptors.” Through these varied lenses, Zwiebel explained, the smell of a human “is not just one odor, it’s not just one molecule.” He continued, “There's actually many, many molecules that activate a whole range of receptors.”

Repellents work by blocking these receptors so a mosquito or tick can’t find you. Essential oils, as Zwiebel explained, “only block a small, discrete number of receptors.” What makes things even trickier is that receptors are different even between closely related species; Zwiebel said he wasn’t convinced that an essential oil that might work for one species would work across a range of others. Repellents such as picaridin and DEET, on the other hand, block a much wider number of receptors on a more consistent basis, as research like Vosshall’s confirms. This offers repellency across many species.

Given what’s at stake with tick and mosquito bites, we recommend using a repellent with a 20 percent concentration of the active ingredient picaridin, supplemented with a permethrin-based repellent used at least on your shoes for tick protection. Both are EPA approved, and their labeling offers specific instructions on the ingredients, the application, and the duration of effectiveness. If you choose to use DEET, which we also endorse, we prefer a 25 percent concentration. After our full review of essential-oil repellents, we agree with the authors of the 2011 study from Malaria Journal, who write that with essential oils, “[t]here is a need for further standardized studies in order to better evaluate repellent compounds and develop new products that offer high repellency as well as good consumer safety.”

Essential oils we tried and would not recommend

We tried out six popular essential-oil repellents, and with all of them it was impossible to know how much repellency to expect, and for how long. Testing them also gave us insight into another potential drawback (or a positive, depending on your tastes): They have extremely strong odors. As Zwiebel put it, “you end up smelling like a rotten fruit basket.” We much prefer the nearly odorless picaridin formulas that we’ve tested. Mosquitoes aren’t the only ones who rely on olfactory cues when deciding who to hang out with.

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DoTerra’s TerraShield takes ambiguous labeling to a new level. The words “bug,” “insect,” and “repellent” are oddly absent from the marketing material and the label. Instead, you can find vague references to “outdoor protection” and “environmental annoyances.” There is no indication of how much to apply, how often, or even if the substance is a repellent at all (we’ve reached out to DoTerra for comment). Customer reviews tell a different story: Nearly all of them describe its efficacy against mosquitoes and other insects, and at least one says, “I would recommend this to anyone looking for a DEET alternative.”

US Organic Anti Bug Spray, Sky Organics Organic Bug Spray, and Nantucket Spider’s Natural Deet-free Bug Repellent have all gone through independent lab testing, but there is still no official recommendation on how often each one should be applied for full coverage from mosquitoes and ticks. US Organic’s testing demonstrates a repellency lasting at least four hours, but the testing protocols are very different from the EPA’s, so it’s impossible to know how the spray would function under the same circumstances that picaridin and DEET are tested under. In other words, that “four hours” is not necessarily the same as the “four hours” indicated on an EPA-approved label. The US Organic and Sky Organics repellents both have high concentrations of soybean oil (40 percent and 23 percent, respectively), which proved to be somewhat effective in the 2002 study published in The New England Journal of Medicine, but there are other studies that disagree.

The Amazon page for Mexitan’s Skedattle All Natural Anti-Bug Spray states that the formula is “16 TIMES AS EFFECTIVE as DEET bug repellents.” What does that even mean? That it lasts 16 times as long? That it blocks 16 times the number of receptors? It’s likely we’ll never know. We reached out to the company multiple times via email and did not get a response.

Shabby Chick Insect Repellent is the most interesting example of what can happen with no regulatory oversight. The repellent contains catnip oil, and the company’s product page states, “Catnip has been proven to be 10x more effective than DEET! No lie!” This is an alluring statement, but our research turned up only one study (PDF) making a similar claim—and, when put in context, it paints a very different picture. First, that study was about spatial repellency not contact repellency, so, as it states, it did “not involve any attractant or host.” Another study did evaluate the contact repellency of catnip oil and found that DEET was more effective. Second, the catnip oil was 10 times as strong as DEET in equal concentrations. We recommend a 25 percent concentration of DEET, yet the Shabby Chick labeling has no indication of how much catnip oil is in its formula. In fact, catnip oil isn’t even listed in the active ingredients. It’s one of the inert ingredients (the only active ingredient is 1 percent cedarwood oil).

In 2020 research, we came across Greenerways Organic Insect Repellent. Like the others it doesn’t have EPA certification, so there is no way to tell how effective it will be against ticks and mosquitoes.

Source: https://www.nytimes.com/wirecutter/blog/essential-oils-terrible-bug-repellents/

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About the Author: Thien Bao

Hello, my name is ThienBao. I am a freelance developer specializing in various types of code.