Permethrin and DEET serve completely different roles in insect protection. DEET is a repellent you apply to your skin to keep bugs from landing on you. Permethrin is an insecticide you apply to clothing and gear that kills insects on contact. They work through different mechanisms, go on different surfaces, and last for very different amounts of time. Understanding what each one does well helps you decide which to use, and whether to use both.
How Each One Works
DEET works by interfering with the sensory receptors insects use to find you. When applied to exposed skin, it creates a vapor barrier that makes it difficult for mosquitoes, ticks, and other biting insects to detect and land on you. It does not kill insects. It simply makes you harder to find.
Permethrin takes the opposite approach. It’s a synthetic version of a compound found in chrysanthemum flowers, and it works by attacking the nervous system of any insect that touches treated fabric. It disrupts nerve cell function, causing muscle spasms, paralysis, and death. A tick crawling across a permethrin-treated pant leg will be incapacitated before it ever reaches your skin. Military testing found that lightweight uniforms treated with 0.5% permethrin provided 97.7% protection from mosquito bites.
The critical distinction: permethrin goes only on fabric, never on skin. DEET goes only on skin (and some fabrics), never as a substitute for permethrin on clothing.
Where and How You Apply Them
DEET comes in sprays, lotions, and wipes formulated for direct skin application. You apply it to any exposed skin not covered by clothing. Products range from under 10% to over 30% concentration, and the percentage determines how long protection lasts, not how strongly it repels. A 10% concentration protects for roughly two hours. A 24% concentration averages about five hours. A 30% product extends that to four to six hours. You reapply when the protection window runs out, just as you would with sunscreen.
Permethrin requires more preparation but far less maintenance. You spray it onto clothing, boots, hats, backpacks, tents, or sleeping bags outdoors in a well-ventilated area, then hang the items to dry completely before wearing them. Never apply it while wearing the clothing, and never apply it directly to skin. Once dry, the treatment bonds to fabric fibers and remains active through multiple washes, typically lasting anywhere from 5 to 20 wash cycles depending on the product. Some factory-treated garments retain effectiveness for even longer.
Duration and Reapplication
This is where the two products diverge most sharply. DEET is a short-term solution. Even the strongest consumer formulations wear off within six hours and need reapplication throughout the day. Sweat, water, and physical activity can shorten that window further.
Permethrin is a long-term treatment. A single application to your hiking pants or field jacket can last weeks to months, surviving repeated trips through the washing machine. You treat your gear once at the start of the season and check periodically to see if retreatment is needed. For people who spend a lot of time outdoors, this dramatically reduces the daily effort of staying protected.
Using Both Together
Permethrin and DEET are not competing options. The most effective insect protection strategy uses both at the same time: permethrin on your clothing and gear, DEET (or another skin repellent) on any exposed skin not covered by treated fabric. This layered approach means insects encounter a lethal barrier on your clothes and a repellent barrier on any skin that’s still exposed. The CDC and most university extension programs recommend this combination for areas with high tick or mosquito activity, particularly where diseases like Lyme, Zika, or West Nile virus are concerns.
Safety Profiles
Both chemicals have been studied extensively and are considered low in toxicity for normal use, but they come with different cautions.
DEET is absorbed through the skin at a modest rate. In human studies, about 5.6% of a dose applied to the forearm was absorbed over eight hours. The most commonly reported side effects are eye irritation (from accidental contact), and about 5% of poison control reports involve skin symptoms like redness, rash, or irritation. Neurological reactions are extremely rare, estimated at roughly one seizure per 100 million users over a nearly 40-year tracking period, and almost all serious cases involved ingestion or wildly excessive application. For children over two months old, concentrations up to 30% are considered appropriate. DEET should not be used on infants younger than two months.
Permethrin’s safety profile on skin is somewhat simpler because you’re not supposed to put it on skin at all. Once dried onto fabric, the amount that transfers to skin is minimal. The EPA rates it low in toxicity for dermal exposure, and it’s not considered a skin sensitizer. In animal studies, any skin or eye irritation from direct contact cleared within 48 to 72 hours.
Effects on Gear and Materials
DEET is a plasticizer, which means it can dissolve or damage certain synthetic materials. This includes some plastics, rubber, vinyl, watch crystals, eyeglass lenses and frames, and certain treated or synthetic fabrics. It’s safe on natural fibers like cotton and wool, but if you’re wearing performance gear made from synthetic blends, DEET spray can degrade the material over time. Keep it away from electronics, watches, and sunglasses.
Permethrin doesn’t carry this risk. Because it’s designed specifically for fabric application, it won’t damage clothing, nylon backpacks, or synthetic tent materials. It bonds to fibers without degrading them.
Cat Toxicity: A Serious Concern
If you have cats, permethrin requires extra caution. Cats lack sufficient amounts of a specific liver enzyme needed to break down permethrin, making them unusually sensitive to it. Exposure to wet, freshly treated clothing or concentrated permethrin products can cause serious toxicity in cats, including tremors, seizures, and potentially death. The key safety measure is to let all treated items dry completely before bringing them indoors, and to keep cats away from the treatment area. Once permethrin is fully dried and bonded to fabric, the risk drops substantially. Dogs, by contrast, metabolize permethrin more effectively and are far less sensitive.
DEET does not pose this same species-specific risk, though keeping any chemical repellent away from pets is still a good practice.
Which One Should You Choose
The answer depends on how you spend time outdoors. For a quick evening on the patio, a DEET spray on exposed skin is simple and effective. For hiking, camping, hunting, or working in tick-heavy areas, permethrin-treated clothing provides a durable base layer of protection that doesn’t require constant reapplication. For serious exposure risk, both together offer the most complete coverage available without a prescription.
If you only want to buy one product for occasional use, DEET is more versatile since it works immediately on any exposed skin. If you’re regularly in the woods or tall grass, investing in permethrin-treated clothing pays off quickly in convenience and coverage. A pair of treated pants and socks can handle the bulk of tick exposure, since most ticks climb upward from ground level, while a moderate-strength DEET product covers your arms, neck, and hands.