DEET is the most widely used insect repellent in the world. Its full chemical name is N,N-diethyl-meta-toluamide, and in pure form it’s a nearly colorless to amber liquid with a faint smell. You’ll find it in sprays, lotions, and wipes at concentrations ranging from about 5% to nearly 100%, and it’s been protecting people from mosquito and tick bites since the U.S. Army developed it in the 1940s for soldiers in insect-heavy environments.
How DEET Actually Works
For decades, scientists assumed DEET simply masked human scent so insects couldn’t find you. The reality is more interesting. DEET works through a dual mechanism: it both confuses an insect’s sense of smell and activates taste receptors that signal “avoid this.” When a mosquito encounters DEET, the chemical triggers the same sensory neurons that respond to naturally aversive, bitter compounds. At the same time, it interferes with the olfactory receptors insects use to track the carbon dioxide and body odors that lead them to you.
The result is that biting insects are simultaneously unable to locate you and actively repelled if they get close. This two-pronged effect is a big reason DEET has remained the gold standard for insect repellents for over 70 years.
What Different Concentrations Mean for You
A higher percentage of DEET doesn’t make the repellent “stronger” in the sense that it repels more aggressively. What it does is make the protection last longer. A product with less than 10% DEET typically offers only one to two hours of protection. A 20% to 30% product covers most outdoor activities. Beyond about 50%, you’re getting diminishing returns, as studies show DEET’s protection time plateaus around that concentration, with no meaningful increase in duration at higher percentages.
For a backyard barbecue, a 10% to 15% formula is usually plenty. For a long hike through tick-heavy woods or an evening in a mosquito-dense area, something in the 25% to 50% range makes more sense. You don’t need 100% DEET for everyday use.
Diseases DEET Helps Prevent
DEET isn’t just about avoiding itchy bites. Mosquitoes carry West Nile virus, Zika, dengue, and malaria. Ticks transmit Lyme disease, Rocky Mountain spotted fever, and several other infections. Using an effective repellent is one of the most practical steps you can take to reduce your risk of these illnesses, especially if you live in or travel to areas where they’re common. The CDC lists DEET as a recommended active ingredient for protection against both mosquitoes and ticks.
Is DEET Safe?
The EPA completed an extensive review of DEET in 2014 and found no risks of concern to human health when it’s used as directed on the skin. The agency continues to affirm that normal use is safe for the general population, including children. No toxic effects have been identified from applying it as a skin-based repellent, and there’s no dietary exposure pathway to worry about.
That said, DEET can cause two types of reactions when misused. Local skin reactions like rashes, irritation, burning, and redness tend to happen with repeated heavy application or very high concentrations above 75%. Systemic reactions, where DEET absorbs through the skin in significant amounts, are rare but can include confusion, drowsiness, muscle weakness, nausea, and in extreme cases, seizures. These serious reactions are almost exclusively linked to massive overuse or accidental ingestion, not normal application.
Using DEET on Children
The American Academy of Pediatrics recommends that insect repellents used on children contain no more than 30% DEET. Parents of newborns and premature infants should be especially cautious about applying DEET or any chemical repellent to their child’s skin. For older children, apply it to exposed skin and clothing rather than letting kids apply it themselves. Avoid their hands, since children frequently touch their eyes and mouths.
How to Apply It Properly
If you’re also wearing sunscreen, apply the sunscreen first and let it absorb, then apply the repellent on top. This order matters because repellent needs to sit on the skin’s surface to work, while sunscreen needs to soak in. Combination sunscreen-repellent products exist, but they’re generally not ideal because sunscreen needs reapplication far more often than repellent does.
You don’t need to reapply DEET on a rigid schedule. Reapply if you start getting bitten, or if heavy sweating, rain, or swimming has washed it off. Always apply it to exposed skin and outer clothing rather than under your clothes. When you come indoors, wash treated skin with soap and water.
What DEET Can Damage
One quirk of DEET that catches people off guard: it dissolves certain plastics and synthetic materials. Rayon and spandex are particularly vulnerable, so be careful spraying near athletic wear, yoga pants, or swimsuit fabrics. DEET can also damage watch crystals, eyeglass frames, phone cases, and some painted or varnished surfaces. Cotton, wool, and nylon hold up fine. If you’re wearing gear you want to protect, apply DEET to exposed skin and keep it off your equipment.
DEET and the Environment
DEET washes off skin and clothing into waterways, which raises reasonable questions about environmental impact. The good news is that it doesn’t accumulate in the food chain. Studies measuring bioconcentration in fish found extremely low levels, meaning aquatic organisms don’t build up DEET in their tissues over time. The chemical is biodegradable under normal environmental conditions, though it breaks down slowly in oxygen-poor environments like deep groundwater or landfill sites. It’s not classified as a persistent or bioaccumulative substance, so while it does show up in water supplies at trace levels, it doesn’t linger or concentrate the way some industrial chemicals do.