Most mosquito repellents are built around one of a handful of active ingredients, with DEET being the most common and widely studied. The rest of the product is a mix of solvents, carriers, and sometimes fragrances that help deliver the active ingredient to your skin. Here’s what’s actually inside the bottle, how each ingredient works, and what the differences mean for you.
DEET: The Most Common Active Ingredient
DEET (N,N-diethyl-meta-toluamide) has been the go-to mosquito repellent since the U.S. military developed it in the 1940s. Early military formulas were 75% DEET dissolved in 25% ethanol. Modern consumer products range from about 5% to 30% DEET, with the rest of the formula made up of inactive ingredients.
DEET works by interfering with a mosquito’s ability to find you. It reduces the volatility of the natural odors your skin gives off, effectively hiding your scent from mosquitoes searching for a host. There’s also evidence that DEET directly activates certain receptors on a mosquito’s antennae, triggering an avoidance response, and that it scrambles the insect’s ability to process attractive human odors. On top of all that, DEET acts as a contact repellent: when a mosquito lands on treated skin, sensory cells on its feet trigger it to fly away.
Concentration matters primarily for duration, not strength. A product with 23.8% DEET provided about five hours of complete protection in a study published in the New England Journal of Medicine, while formulations under 5% wore off much sooner. Higher concentrations don’t repel mosquitoes more effectively in the moment; they just last longer before you need to reapply.
Picaridin, IR3535, and Other Synthetic Options
Picaridin (also called icaridin) is a synthetic compound modeled after a chemical found in black pepper plants. It provides protection comparable to DEET at similar concentrations and has a lighter feel on the skin with less of the oily residue DEET can leave behind. Products typically contain 5% to 20% picaridin.
IR3535 (ethyl butylacetylaminopropionate) is a synthetic amino acid derivative common in European repellent formulas and increasingly available in the U.S. It works through similar olfactory disruption as DEET but tends to offer shorter protection times at equivalent concentrations. You’ll find it in some lotion and spray products marketed as gentler alternatives.
2-Undecanone (also called methyl nonyl ketone) is a newer option derived from wild tomato plants. The EPA classifies it as a biopesticide. It breaks down rapidly in soil, with a half-life of about half a day, making it one of the more environmentally friendly choices. It’s available at lower concentrations and generally provides shorter protection than DEET or picaridin.
Plant-Based Repellents
Oil of lemon eucalyptus (OLE) is the only plant-derived repellent recommended by the CDC. The active compound, PMD (para-menthane-3,8-diol), occurs naturally in lemon eucalyptus leaves but is usually produced through a chemical refinement process for commercial products. At 30% concentration, it provides roughly two hours of protection. It should not be used on children under three years old.
Citronella, soybean oil, geraniol, and other essential oils show up in “natural” repellent products, but they generally provide significantly shorter protection, often under an hour, and need frequent reapplication. These oils evaporate quickly from skin, which is why they fade fast. Their concentrations in consumer products vary widely and aren’t standardized the way DEET or picaridin formulas are.
What Else Is in the Bottle
Active ingredients typically make up only a fraction of any repellent product. The remaining formula consists of inactive (sometimes called “inert”) ingredients that shape how the product feels, smells, and works in practice. These include solvents like ethanol or isopropanol that dissolve the active ingredient and help it spread evenly across skin. Carriers and diluents adjust the concentration so the product can be applied safely and comfortably.
Aerosol sprays contain propellants that force the product out of the can. Lotions and creams use emulsifiers and thickeners to create a formula that stays on your skin longer than a liquid would. Some products add fragrances to mask the chemical smell of the active ingredient. Wipes use a pre-saturated cloth as the delivery system, often with a slightly different solvent balance to keep the fabric moist in its packaging.
The delivery format changes how long the repellent lasts. Lotions and controlled-release formulas tend to provide longer protection because they sit on the skin surface and release the active ingredient gradually. The military eventually moved from its original ethanol-based DEET spray to a longer-lasting, ethanol-free formula with just 33% DEET, specifically because the controlled-release technology extended protection without needing a higher concentration.
Permethrin: For Clothing, Not Skin
Permethrin is a synthetic version of pyrethrins, insecticidal compounds found naturally in chrysanthemum flowers. It’s not a repellent in the traditional sense. Instead, it’s a contact insecticide: when a mosquito lands on permethrin-treated fabric, the chemical disrupts the insect’s nervous system, causing paralysis and death. You apply it to clothing, gear, and mosquito nets rather than directly to skin.
Less than 2% of permethrin is absorbed through skin on contact, which is why it’s considered safe even for treating clothing worn by children and infants. Treated clothing remains effective through multiple washes. Many outdoor brands sell pre-treated shirts, pants, and socks, or you can buy permethrin spray to treat your own gear. For the best protection in mosquito-heavy areas, the combination of a skin-applied repellent like DEET or picaridin plus permethrin-treated clothing covers both exposed and covered skin.
Safety During Pregnancy and for Children
The CDC, the American College of Obstetricians and Gynecologists, and other major health organizations recommend using EPA-registered repellents during pregnancy and while breastfeeding. The reasoning is straightforward: the diseases mosquitoes carry pose a far greater risk than the repellent itself. Less than 10% of DEET applied to skin enters the bloodstream, and most studies have not found an increased risk of birth defects from DEET use.
Picaridin, IR3535, PMD, and 2-undecanone haven’t been studied specifically in human pregnancy, but because so little of these ingredients is absorbed through skin when used as directed, they’re generally considered acceptable. If you’re breastfeeding, the main precaution is to keep repellent away from the nipple area so the baby doesn’t ingest any.
For children, the key guidelines are practical: apply repellent to your own hands first, then rub it onto the child’s skin to avoid getting it near their eyes or mouth. Don’t apply it to a child’s hands, since kids frequently touch their faces. Oil of lemon eucalyptus products shouldn’t be used on children under three.
Environmental Considerations
DEET is the most studied repellent in terms of environmental impact, and it shows up consistently in water testing. Researchers have detected it across aquatic ecosystems at concentrations up to about 32 micrograms per liter. Its breakdown half-life ranges from a few days to a few weeks depending on conditions, so it doesn’t persist long-term in the environment. Its primary breakdown product, 3-methylbenzoate, degrades relatively quickly as well.
At the concentrations typically found in waterways, DEET doesn’t appear to cause acute toxicity in aquatic organisms. However, there’s evidence of subtler chronic effects, including disrupted reproduction and altered behavior in aquatic animals. The concern grows when DEET interacts with other pollutants already present in the water, potentially creating combined effects that are harder to predict. Picaridin and plant-based options have smaller environmental footprints, though they’ve also been studied far less extensively.