Most bug sprays rely on one of four EPA-registered active ingredients: DEET, picaridin, IR3535, or oil of lemon eucalyptus. Each works differently, lasts a different amount of time, and comes with its own tradeoffs. The inactive ingredients (fragrances, solvents, propellants) make up the rest of the can or bottle, but it’s the active ingredient and its concentration that determine how well a repellent actually works.
DEET: The Most Common Active Ingredient
DEET has been the go-to insect repellent since the 1950s and remains the most widely available option. It works by interfering with receptors on a mosquito’s antennae that detect the lactic acid and carbon dioxide your body gives off. Insects exposed to DEET essentially lose their ability to find you.
Concentration matters more than most people realize. A product with 10% DEET protects for roughly two hours, while 30% DEET can last up to eight hours. Going above 30% doesn’t add much extra time; it mainly extends protection by diminishing increments. Higher concentrations can feel greasy or tacky on skin, and DEET is known for dissolving certain plastics, synthetic fabrics, and watch faces. If you’ve ever noticed a bug spray eating into a rain jacket or a phone case, DEET was likely the culprit.
Picaridin: A Less Irritating Alternative
Picaridin works by stimulating sensory hairs on a mosquito’s antennae, which prevents the insect from recognizing you as a host. It both repels and deters feeding, so even insects that land on treated skin tend to leave without biting. Products with 20% picaridin offer protection comparable to 20% DEET against mosquitoes and ticks.
Where picaridin stands out is in how it feels. It doesn’t have the oily residue DEET leaves behind, won’t damage plastics or synthetic clothing, and has almost no odor in most formulations. The EPA classifies it as practically non-toxic by inhalation and not a skin irritant or sensitizer. It can cause slight to moderate eye irritation, so you still want to keep it away from your face when spraying. For people who dislike the feel of traditional bug spray, picaridin is the ingredient to look for on the label.
Oil of Lemon Eucalyptus and PMD
Oil of lemon eucalyptus (OLE) is a plant-derived repellent whose key compound, p-menthane-3,8-diol (PMD), is structurally similar to menthol. While the raw oil comes from eucalyptus leaves and twigs, commercial products use a chemically synthesized version of PMD. It repels mosquitoes, biting flies, and gnats, and the EPA has confirmed it meets effectiveness standards for public health pests.
OLE products with 30% PMD can provide protection lasting several hours, putting them in a similar range as moderate-concentration DEET. The main limitation is age: the American Academy of Pediatrics and the CDC say not to use products containing OLE or PMD on children younger than 3. In animal studies, the compound showed no adverse health effects aside from eye irritation, which is why labels instruct you to spray it into your palm first and then spread it onto your face and neck rather than spraying directly.
IR3535: Common in Gentler Formulations
IR3535 is a synthetic compound modeled after a naturally occurring amino acid. The EPA classifies it as a biopesticide because of its structural relationship to substances found in nature. It works like other repellents by disrupting an insect’s ability to detect a human host through smell and taste. You’ll find IR3535 in products marketed as family-friendly or sensitive-skin formulas, often at concentrations around 20%. It repels mosquitoes, ticks, flies, and other biting insects, though some users find it slightly less effective against ticks than DEET or picaridin at similar concentrations.
Permethrin: For Clothing, Not Skin
Permethrin is different from every other ingredient on this list because you spray it on clothing, gear, and shoes rather than on your skin. Instead of just repelling insects, permethrin attacks their nervous systems. It disrupts sodium channels in neurons, causing muscle spasms, paralysis, and death. A mosquito or tick that lands on permethrin-treated fabric doesn’t just fly away; it’s incapacitated. This makes permethrin especially valuable for tick protection, since ticks crawl across clothing before reaching skin.
Treated clothing can remain effective through multiple washes, and factory-treated garments often last 70 or more washings. Permethrin breaks down quickly on skin and is considered safe for humans to wear on clothing, but it poses serious risks to two groups: cats and aquatic life.
Cats lack the liver enzyme needed to metabolize permethrin efficiently. A cat exposed to concentrated permethrin, whether directly or through close contact with a recently treated dog, can develop muscle tremors, seizures, incoordination, and agitation within hours. In one documented case involving 11 cats exposed to products containing 45 to 65% permethrin, all required hospitalization and four died. If you treat clothing with permethrin, keep it away from cats until it’s fully dried, and never apply a dog-specific flea product containing permethrin to a cat.
Permethrin is also extremely toxic to fish and aquatic invertebrates at concentrations measured in parts per billion. Avoid spraying near streams, ponds, or storm drains, and don’t wash freshly treated clothing where rinse water could reach waterways.
Essential Oils and “Natural” Repellents
Citronella candles, peppermint sprays, and lemongrass wristbands are popular, but research consistently shows they provide far less protection than EPA-registered ingredients. In testing at New Mexico State University, citronella and lemongrass oils in a 10% lotion emulsion lasted about 30 minutes before mosquitoes resumed biting. Clove oil, cinnamon oil, and geraniol performed better, providing complete protection for just over an hour, but that’s still a fraction of what a 20% DEET or picaridin product delivers.
The short duration means frequent reapplication, and some essential oils (cinnamon and clove in particular) can irritate skin at higher concentrations. If you prefer plant-based options, products containing OLE or PMD are the only ones with EPA registration and proven multi-hour efficacy. Everything else on the “natural” shelf is in a different performance category.
How Concentration Affects Protection Time
The single most useful thing on a bug spray label is the percentage of the active ingredient. A product with 5% DEET and one with 30% DEET both repel mosquitoes, but the 5% version wears off in about 90 minutes while the 30% version lasts roughly five to eight hours. The same principle applies to picaridin and OLE. Higher concentration doesn’t make the repellent “stronger” in the sense of creating a bigger barrier. It makes it last longer before it evaporates off your skin.
For a short walk around the neighborhood, a lower-concentration product is fine. For a full day of hiking or an evening outdoors in a mosquito-heavy area, you want 20% or higher of whichever active ingredient you choose. Combining a skin-applied repellent (DEET, picaridin, or OLE) with permethrin-treated clothing gives the most complete protection, especially in areas where tick-borne illness is a concern.
Safety for Children and Pregnancy
The American Academy of Pediatrics and the CDC both recommend EPA-registered repellents, including DEET, for children. The key guidelines by age are straightforward. For infants under 2 months, avoid repellents entirely and use mosquito netting instead. For children under 2 years, apply DEET or picaridin sparingly and avoid applying it to their hands, since young children frequently put their hands in their mouths. Products containing OLE or PMD should not be used on children under 3.
For pregnant individuals, EPA-registered repellents including DEET and picaridin are considered safe when used as directed. This is especially relevant in regions with mosquito-borne illnesses like Zika or dengue, where the risk of not using repellent outweighs concerns about skin absorption. Regardless of age or pregnancy status, apply repellent to exposed skin only, wash it off once you’re indoors, and never spray it under clothing.