Whether you’re traveling to a mosquito-ridden area or just planning to lounge around your backyard this summer, having a good insect repellent on hand is key to staying bite-free. Diseases transmitted by mosquitoes and other insects are on the rise worldwide. For the first time in over two decades, there have even been several cases of local transmission of malaria in the U.S.—in Texas and Florida.
The CDC recommends insect repellents containing one of the following active ingredients that are EPA-registered: picaridin, DEET, IR3535, oil of lemon eucalyptus (or its synthetic derivative PMD, for p-menthane-3,8-diol), or 2-undecanone. EPA registration means the product has “been evaluated and approved for human safety and effectiveness when applied according to instructions on the label” and assures that “the product does not pose risks to vulnerable populations, including children and pregnant women.”
Meanwhile, the Environmental Working Group (EWG), a nonprofit public health and environmental advocacy and research group in Washington, D.C., first recommends any of these three ingredients—DEET (at less than 30 percent concentration), IR3535 (at 20 percent), or picaridin—because they are effective and have “very low toxicity concerns” when used properly. Then, alternatively, EWG notes that you can buy an insect repellent with either oil of lemon eucalyptus/PMD or 2-undecanone—and try different ingredients if one doesn’t work for you.
From DEET to permethrin
DEET: The percentage concentration of this synthetic chemical—N, N-diethyl-meta-toluamide—in products varies greatly, but it’s best to go with a concentration no greater than 30 percent to reduce the chance of eye or skin irritation. Don’t apply the product on skin that’s already irritated or has an open wound or cut, and don’t apply it under your clothing (rather, you can treat your clothes with permethrin; see below).
Picaridin: Picaridin is chemically synthesized to mimic an insect-repelling chemical found in the pepper plant. A higher concentration (20 percent) can provide protection from insects for more than 12 hours, while lower concentrations (5–10 percent) can protect for about five to 12 hours. Unlike with DEET, it has a low risk of skin or eye irritation, has little odor, and won’t damage fabrics or plastic.
Oil of lemon eucalyptus: This chemical is derived from the oil in the leaves of the Eucalyptus citriodora (aka lemon-scented gum) tree, not to be confused with the essential oil called lemon eucalyptus oil, which is completely different. Its repellent properties are similar to those of low concentrations of DEET. Repellents with this chemical—or the synthetic version PMD—come with a high risk of eye irritation. If you get any in your eyes, wash it out immediately to prevent damage.
IR3535 (aka Merck 3535): This chemical, which is structurally related to the naturally occurring amino acid beta-alanine, has been used for years in Europe as an insect repellent. But a low concentration (less than 10 percent) may not be effective. In addition, its use comes with a moderate risk of eye irritation, so avoid using it anywhere near your eyes. Products that contain IR3535 include Coleman Skin Smart and Avon Skin So Soft Bug Guard Plus IR3535 Expedition.
2-Undecanone: This is derived from wild tomato plants. Due to its strong odor, it’s known for its animal repellent properties—keeping away raccoons, dogs, and cats, for example. As an insect repellent, it’s available in few products, but we found at least this one, BioUD. It’s hard to determine the extent of any adverse effects because of its limited use.
Nootkatone: The CDC was involved in developing this brand-new insect repellent derived from the Nootka cypress (aka Alaska yellow cedar tree) as well as from citrus fruits and some herbs. At this time, products containing the ingredient are not available in the marketplace, but it’s anticipated this will change soon.
Permethrin: This chemical is applied to fabrics—to both clothing and ancillary items such as a tent or bedding. It’s not to be used on skin. When using permethrin on your clothes, you still need to rely on an insect repellent on your skin to have a high assurance of protection from insects. The protection can last weeks to months depending on how often you wash the treated fabric. Wash permethrin-treated clothing separately from other clothes. Some companies sell lines of permethrin-treated clothing, and at least one company, Insect Shield, offers a service where you send in your own clothes to be treated, which provides longer-lasting protection than treating them yourself with commercial sprays.
Botanicals: These include essential oils, such as citronella, lemongrass, peppermint, thyme, cinnamon, geranium, lavender, or clove. Products typically contain several of them together because, as noted in a review paper, there appears to be a synergistic insect-repelling effect when the oils are combined. One such botanical product is Herbal Armor, which has, among the ingredients, citronella, lemongrass, peppermint, cedarwood, and geranium oils. Natural essential oils are exempt from EPA registration, and they don’t have to be tested for safety or effectiveness, the latter of which can vary substantially. Generally, however, their effectiveness—if any—is considered to be limited to somewhere between half an hour and two hours, so they have to be reapplied frequently.
B vitamins: Though it’s still commonly believed that taking B vitamins is a way to prevent mosquito bites, there are, in fact, no well-controlled studies providing that evidence. For example, according to a 2022 review paper, the reported insect-repellent benefits from vitamin B1 (thiamine) came mostly from anecdotal reports or poorly controlled studies.
BOTTOM LINE: So, where does that leave you when you want to armor up against mosquitoes? The EPA has a handy search tool on its website that helps you determine the best skin-applied repellent for your situation, based on several factors, including how long you need to be protected and from what insects (mosquitoes, ticks, or both). For instance, if you will be out for four hours or less and want protection from just mosquitoes, the search tool brings up 85 different EPA-registered products to choose from containing citronella, IR3535, DEET (5–30%), picaridin, or PMD. If you are looking for longer-lasting protection (9–12 hours), the database lists seven products limited to IR3535, DEET (at very high concentrations), and picaridin. Need protection for even longer (13–16 hours)? You have a choice of three products, all containing picaridin.
The EPA doesn’t endorse any of these products, and the list does not include all that are available. If you want to try any of the other ingredients we discussed, you can see if they work, but be prepared for some bites. If one particular ingredient isn’t effective enough, your overall best bet is to try others to see if they work better.
- Apply sunscreen first and then the insect repellent, but be aware that the repellent can reduce the effectiveness of the sunscreen, which you’ll have to reapply often.
- There’s no reason to do a heavy application of insect repellent. Use just enough to cover your skin.
- Never use any insect repellent on skin that’s irritated or has a cut or open wound.
- If your hands come into contact with insect repellent when applying it (such as if you use lotions or wipes), be sure to wash your hands afterward. And when you’re done with your outdoor activities, use soap and water to wash the insect repellent off your skin.
- If you’re traveling to parts of the world where mosquitoes are vectors for diseases like malaria, in addition to using insect repellent, you should wear long-sleeve shirts and long pants tucked into your socks; use permethrin-treated clothing for extra protection. Avoid going out after dusk or at dawn (though some mosquitoes are active all day)—and sleep under mosquito netting if possible.
