What’s Really in Your Insect Repellent
This guide to what’s really in your insect repellent helps you avoid toxic chemicals and look for a more environmentally friendly insect repellent instead. If you’re like most people, you want to protect yourself and your family from insect bites—and from harmful chemicals that can harm you and the environment.
Scientists are always looking for better ways to foil bugs that leave itchy welts in their wake. Despite the many tools being studied, from tick–killing fungus to genetically modified mosquitoes, insect repellent is still the first line of defense. It’s a personal protection measure that is easily accessible, affordable and any individual can take into their own hands.
Insect repellent is an important first line of defense. In the U.S., the mosquito–borne West Nile virus is thought to have infected nearly 7 million people since it first appeared in New York in 1999, and every year close to half a million people get Lyme disease after a tick bite.
But not all repellents provide equal protection. It turns out that what matters most is not the brand or type of repellent (spray, lotion, or wipe) but the active ingredient and its concentration in the formula. Be sure to try our homemade natural insect repellent, it is organic, effective, and safe for the whole family.
The list of products available on the market changes slightly from year to year, but insect repellents whose active ingredient is DEET, at concentrations of 25–30%, even some (but not all) with a concentration of 15% DEET can still be effective. Some (but again, not all) repellents with 30% oil of lemon eucalyptus (OLE) and 20% picaridin provide long–lasting protection.
The Rise of Lyme Disease
In the U.S., the range of the black–legged tick (which transmits Lyme disease) has grown over the past two decades. Lyme disease, which gets its name from the Connecticut town where it was first identified, has spread throughout the U.S. due to a changing climate, increased suburbanization, and reforestation in the Northeast, among other reasons.
Early symptoms of Lyme disease often include a rash, sometimes in a bull’s–eye shape, and a fever. Untreated, symptoms can progress to arthritis, nerve pain, and heart palpitations. Today, cases of Lyme disease are found in nearly every state.
The Zika Virus Crisis
As the Zika crisis bears down, the advice to Americans, especially to women who are pregnant or may become pregnant is to cover up and use insect repellents most likely to drive away Aedes aegypti species mosquitoes, suspected as the primary carriers of the Zika virus. Don’t travel to places where Zika cases are being reported if possible. Pay careful attention to the travel notices posed by the U.S. Centers for Disease Control and Prevention (CDC) and for updated information on Zika.
Commercial repellents containing DEET, catnip essential oil (Nepeta cataria, also known as catmint), citronella essential oil, IR 3535®, p–Menthane–3,8–diol (PMD), oil of lemon eucalyptus (OLE), picaridin, and 2–undecanone offer strong protection from the Aedes aegypti mosquito for at least four hours in laboratory conditions.
Scientists have generally found commercial insect repellents to be safe for pregnant women and their unborn children. The risk of Zika infection is far more serious than side effects from repellent chemicals, provided you use products as directed. Zika can be transmitted through sexual contact. The CDC says it stays in longer in the sperm of infected men than in their blood. If your partner could be infected, use protection.
Tips for Applying Insect Repellent
No insect repellent is 100% effective, so take extra precautions to avoid bites.
- Apply spray to exposed skin and clothes. If you need both sun and insect protection, the CDC recommends buying two separate products and applying sunscreen first and then insect repellent. Never apply commercial repellents under your clothing because they could cause skin irritation. Natural insect repellents are usually safe to apply everywhere as long as you’ve performed a 24–hour skin patch test first. Before spraying on clothes, test (commercial and natural) repellents out on a small piece of fabric to make sure they won’t cause damage.
- Leave no exposed skin unsprayed. Mosquitoes and ticks are good at finding unprotected skin. Cover up with pants and long sleeves when possible, especially when you need protection from sun and insects. To protect your face—and to apply repellents to children—first spray your hands, then rub on your face or on your child. A thin film of repellent is sufficient. Wash your hands after applying to avoid getting any repellent in your eyes or mucous membranes.
- Reapply as directed. Reapply after swimming and sweating. Check the product label for a suggested time frame, which may range anywhere from 2–8 hours. Natural insect repellents have a shorter time frame, usually no more than 1–2 hours. A good guideline is to reapply it when you notice mosquitoes are biting again. However, commercial repellents have limits on a maximum number of applications per day. Make sure to read the label carefully and follow directions for use. Natural insect repellents are usually safer to reapply as often as needed.
What is DEET and What Makes it Effective?
When it comes to active ingredients that can ward off bugs, DEET ranks high on the list. It is “broad spectrum,” meaning it works on a wide variety of bugs, including mosquitoes, ticks, and flies. DEET was discovered in the 1940s after the U.S. military and the Department of Agriculture (USDA) jointly screened more than 6,000 different compounds looking for ones that would repel mosquitoes. A chemical closely related to DEET was found to be highly effective, then refined slightly to reduce its tendency to irritate skin.
Thus N,N–diethyl–meta–toluamide, or DEET, was born and eventually registered for use in consumer products in 1957. Though scientists found out long ago that DEET works, they still don’t know exactly why. Theories abound. DEET may mask the odor of humans, confuse the odor–sensing abilities of mosquitoes, or simply compel them to move away, perhaps because it resembles a natural substance they’ve evolved to avoid.
But it may be more than just odor at work. Even mosquitoes bred without the ability to sense the smell of DEET appear to sense the chemical with their legs when they land on it, and fly away without biting, according to a 2019 study published in the journal Current Biology. It’s also possible that DEET is so effective against mosquitoes because it’s working on more than one and maybe several levels at the same time, according to research on insects’ sense of smell at the Johns Hopkins University School of Medicine.
There is even less knowledge about why DEET also repels ticks, though the mechanisms (or MOA, the causal, biochemical manner in which it produces effects) are likely different than with mosquitoes. Ticks don’t have the same odor–sensing body parts as mosquitoes. Instead, they have a sensory mechanism unique to ticks called the “Haller’s organ”, which we still know very little about, according to research at Brandon University in Manitoba, Canada. But scientists think it’s the main way ticks sense their surroundings.
Ticks, which generally hitch a ride as you pass them in brush or tall grasses, are less likely to attach themselves to your skin if they sense DEET, and they’ll avoid spots on your skin where DEET is applied. That’s one reason it’s important to apply repellent carefully to all exposed skin in order to avoid ticks.
Safety of DEET
DEET has been available to consumers for more than 60 years, and it’s estimated that people use it millions of times each year. In all that time, only a few cases of harm linked to it have been reported. A 1998 Environmental Protection Agency (EPA) analysis investigating health effects of DEET found that since 1960, the estimated incidence of seizures with a connection to DEET exposure was 1 per 100 million users.
A 2007 EPA chemical summary report on DEET reported that many of the instances of adverse neurological effects were linked with ingestion or repeated dermal exposure inconsistent with label directions. Meaning DEET may pose risk if ingested or used improperly. Always use DEET–powered repellent as directed. Always keep repellents well out of children’s reach.
Higher concentrations of DEET than 30% have never been tested since it is considered unnecessary for effectiveness and long–lasting protection. The Centers for Disease Control and Prevention (CDC) recommends it as a safe option for adults, children older than 2 months, and even pregnant women. Still, no chemical is without risks, and DEET must be used properly in order to be safe.
According to the National Pesticide Information Center (NPIC), avoid applying DEET underneath your clothes (use it only on exposed skin and on the outside of clothing), and do not reapply it too frequently. Not following label instructions could lead to getting a higher dose of DEET than intended. Plus, DEET can degrade certain synthetic materials like polymers, so it shouldn’t be applied to clothing made with synthetic fibers.
Regarding the long–term risks of exposure to DEET, according to a 2008 fact sheet by the NPIC, “researchers have not found any evidence that DEET causes cancer in animals or humans,” and there’s no clear evidence of other long–term risks of topical use.
What Are OLE, Picaridin, and IR 3535® and What Makes Them Effective?
OLE was brought to the attention of U.S. scientists in the 1990s, when they learned that a Chinese product called “Quwenling” was repelling mosquitoes much better than other plant–based products. One of its major components is the chemical p–Menthane–3,8–diol (or PMD), which gives OLE its repellency.
The name “oil of lemon eucalyptus” (OLE) is actually a misnomer. It comes from the Australian plant Corymbia citriodora (or lemon–scented gum), which was considered part of the Eucalyptus genus but has since been reclassified. OLE is not a true essential oil, unlike lemon and eucalyptus essential oils, because it’s refined and concentrated. Although it is an ingredient that’s often very effective.
Picaridin, also called icaridin, is a synthetic patented chemical developed by Bayer AG in the 1980s and 1990s. Its structure is similar to piperidine, a phytochemical compound that occurs naturally in certain plant members of the genus Piper (pepper) in the Piperaceae family. It has been available to U.S. consumers since 2005 and is especially popular as an insect repellent in Europe and Australia. Look for it at 20% concentration.
IR 3535® (ethyl butylacetylaminopropionate), or 3–[N–Butyl–N–acetyl]–aminopropionic acid, is the trade name of an insect repellent developed and commercialized by German multinational science and technology company Merck KGaA. IR3535® repellent mimics a naturally occurring amino acid ß-alanine, which gives the repellent ingredient a high toxicological and environmental profile combined with effectiveness. Look for it at a 20% concentration.
Safety of OLE, Picaridin, and IR 3535®
There has not been much research on OLE and picaridin, but evidence suggests that they’re safe when used according to the label. The EPA has classified OLE and IR 3535® as biopesticides, which means that they are a naturally occurring chemical compound considered to be a lower risk than more conventional industrial agricultural pest–control chemicals.
There is risk that it can be harmful if it gets in your eyes. Its safety has not been studied in young children so it shouldn’t be used on children younger than 3. There is also a small risk of skin irritation with picaridin. There are no studies or research on the long–term effects of these two ingredients.
Commercial Repellents With the Same Active Ingredients Can Perform Differently
Some repellents with the same labeled active ingredient can last for a long time while others don’t. That’s partly because—unlike with cosmetics or other personal care products—manufacturers of EPA–registered repellents aren’t required to disclose all of the ingredients. It is possible that some of the non–active ingredients in a given repellent impact how well the repellent performs.
At the Department of Entomology at the University of Kentucky, academic research study on commercial insect repellent formulations is limited. This is because manufacturers do not provide their formulas to researchers for study and testing, claiming they are trade secrets. Thereby making independent scientific studies of insect repellents and how a repellent’s non–active ingredients may be contributing to its efficacy unavailable to consumers.
Natural Insect Repellents and Their Efficacy
Natural insect repellents, meaning those whose active ingredients are essential oils (EOs), are usually largely underrated. Lemongrass EO, cedarwood EO, citronella EO, catnip EO, and peppermint EO are among the common ingredients found in natural insect repellents. These ingredients come from plants that have been repelling insects for millions of years according to research on entomology and toxicology at Iowa State University. These ingredients are safe, organic, and effective.
The drawback to using essential oils is that the molecules that make up these compounds, known as terpenes, are small and light. So while they’re very effective repellents they evaporate quickly from your skin. Which means they don’t last as long as other mass–produced manufactured products. They need to be reapplied more frequently. Essential oils are always a safer option but are not entirely without risk.
The quality and potency of essential oils can vary greatly between manufacturers and their efficacy can be unpredictable, according to research on toxicology and physiology at the Department of Entomology at Virginia Polytechnic Institute and State University.
Some essential oils may work for a short period of time. But others are ineffective against Aedes aegypti mosquitoes. Due to the serious risks posed by Zika, we do not recommend blends of essential oils for people at risk of mosquito–borne infection.
Safety of Natural Insect Repellents
Essential oils are highly concentrated phytochemical compounds that may need to be diluted into a carrier oil, ointment, gel or cream form before it can be applied to skin. Topical use of some essential oils may not be safe for people with hypersensitive skin, or women who are pregnant or breastfeeding. Some essential oils may have serious interactions with certain medications.
Use essential oils with extreme caution on children. Some brands clearly label their essential oils “KidSafe” on the bottle if it can be used on children ages 2–10. When applying any essential oil topically (on your skin), always perform a 24–hour skin patch test first using 1–2 drops, read how for further details. Avoid essential oils in eyes or in mucous membranes. Never ingest essential oils. Essential oils should never be used on broken or damaged skin. Do not apply directly to open wounds.
If you are interested in trying any essential oil, be sure to choose a product that is authentic 100% pure and organic. Essential oils are always packaged in tightly–sealed dark glass bottles. Keep essential oils in a cool, dry place, away from direct sunlight and extreme heat and cold temperatures. Signs that an essential oil has expired includes changes in scent, texture and color.
Other Phytochemical Compounds
Research is ongoing to discover plant–based repellents that will evaporate less quickly. A few more effective plant–based repellents are already on the market. P–Menthane–3,8–diol (PMD), which gives oil of lemon eucalyptus its potency, is a terpene–like compound.
So is a tomato–derived active ingredient, 2–undecanone which is registered with the EPA as an effective repellent ingredient. Although it is difficult to find products with this ingredient available on the market in the U.S.
There’s also a new active ingredient called nootkatone, which is derived from grapefruit skin and Alaska yellow cedar trees. It is a sesquiterpene, a heavier terpene molecule that was registered with the EPA in 2020. It’s so new, in fact, that there aren’t any commercial insect repellents on the market that contain it. According to the EPA it should have good efficacy against biting bugs.
EPA’s Guidelines for Skin–Applied Repellent Ingredients
These are active ingredients in EPA–registered skin–applied insect repellents. Read more about EPA regulation of skin–applied insect repellents.
- Catnip oil—EPA pesticide regulatory information (Nepeta cataria, also known as catmint)
- Oil of citronella (also used in unregistered products that meet the requirements for exemption from registration)
- DEET
- IR 3535®—EPA pesticide regulatory information (3–[N–Butyl–N–acetyl]–aminopropionic acid, ethyl ester)
- p–Menthane–3,8–diol (PMD)—EPA pesticide regulatory information
- Oil of Lemon Eucalyptus (contains PMD, but is a separately regulated pesticide chemical)
- Picaridin
- 2–undecanone—EPA pesticide regulatory information (or methyl nonyl ketone)
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Sources:
Most Effective Insect Repellent Ingredients | Deet, Picaridin, OLE
https://www.consumerreports.org/health/insect-repellent/which-insect-repellent-ingredients-are-most-effective-a9746785695/
Skin-Applied Repellent Ingredients | US EPA
https://www.epa.gov/insect-repellents/skin-applied-repellent-ingredients
Avoid Insects and Toxic Chemicals — Bug Repellent | EWG
https://www.ewg.org/areas-focus/personal-care-products/bug-repellent
Protect Yourself From Bug Bites With an Effective Repellent
JUNE 29, 2020