For most situations, 20% to 30% DEET provides solid protection against mosquitoes, ticks, and biting flies. Going higher than 50% doesn’t make the repellent work better; it only extends how long it lasts, and even that gain is minimal past the 50% mark. The real question isn’t just “how much” but what you’re doing, how long you’ll be outside, and who’s wearing it.
The 10% to 50% Range, Explained
DEET’s effectiveness peaks at around 50%. Products above that concentration don’t repel insects any more effectively. They just stretch the duration slightly. A 95% DEET spray, for example, advertises about 10 hours of protection. A 50% product claims 8 to 10 hours. A 30% lotion gets you roughly 8 hours. So doubling or tripling the concentration from 30% to 95% buys you, at most, a couple extra hours.
For most adults spending a few hours outdoors, 10% to 35% DEET is enough. A product in the 20% to 30% range hits the sweet spot: long-lasting enough for a hike, a barbecue, or an evening outside, without unnecessary chemical load on your skin. If you’re heading into heavy mosquito territory for a full day, or traveling somewhere with malaria or dengue risk, stepping up to 50% makes sense for the extended duration. There’s little practical reason to go above that.
Ticks, Mosquitoes, and Other Biters
DEET works against mosquitoes, ticks, biting flies, chiggers, and fleas. There isn’t a separate, higher threshold specifically required for ticks versus mosquitoes. That said, effectiveness does vary among species. Tick bites tend to happen during prolonged activity in wooded or grassy areas, so longer-lasting protection matters more. A 30% to 50% product applied to exposed skin (and permethrin-treated clothing, if you want belt-and-suspenders protection) is a reasonable approach for tick-heavy environments.
Children and Infants
The American Academy of Pediatrics recommends that insect repellents used on children contain no more than 30% DEET. For most kids, a 10% to 20% product is practical for shorter outdoor time, while 25% to 30% covers longer stretches. Parents of newborns and premature infants should be especially cautious about applying DEET or other chemicals to their child’s skin. Apply it to clothing rather than skin when possible, avoid hands and faces (kids touch their mouths), and wash it off once they come inside.
Using DEET During Pregnancy
Animal studies using doses 10 to 100 times higher than proportional human exposure have not shown an increased risk of birth defects from DEET applied to skin. A human study covering the second and third trimesters found no elevated risk of birth defects or developmental problems either. No published data exists on first-trimester exposure specifically, but major health agencies generally consider DEET safe during pregnancy when used as directed.
For breastfeeding, no studies have measured how much DEET transfers into breast milk. Only 5% to 15% of DEET applied to skin gets absorbed, and blood levels become undetectable about four hours after application. Some experts suggest avoiding breastfeeding during that four-hour window as a precaution. Keeping DEET off your hands and chest before nursing is also a practical step. The simplest approach for pregnant or nursing individuals: pick the lowest concentration that covers the duration of your outdoor activity.
When to Reapply
The hours listed on a product label assume moderate conditions. In reality, sweating, high heat, rain, and swimming all shorten how long DEET stays effective on your skin. If you’re exercising hard, working outdoors in humid weather, or going in and out of water, reapply more often than the label suggests. A 30% product that lasts 8 hours while you’re sitting on a porch might need reapplication after 4 or 5 hours if you’re sweating through a trail run.
DEET is not water-resistant in the way sunscreen can be. If you towel off after swimming, you’ve removed most of the repellent. Reapply as you would after any activity that physically removes the product from your skin.
DEET and Sunscreen Together
If you need both sun and bug protection, use them as separate products rather than a combination formula. Apply sunscreen first, let it absorb for a few minutes, then apply DEET on top. Clinical testing has found that sunscreen doesn’t reduce DEET’s repellent effectiveness when layered this way. The reverse isn’t quite true: DEET can reduce sunscreen’s SPF by about a third. Since most people already under-apply sunscreen (effectively cutting its real-world SPF by 50% to 75%), this stacking effect means you should use a higher SPF than you think you need, or reapply sunscreen more frequently.
Side Effects at High Concentrations
Used normally on skin, DEET’s side effects are mild: occasional redness, irritation, or hives that go away once you wash it off. More serious skin reactions, including blistering and scarring, have been reported with long-term, repeated use of high-concentration products (above 50%).
The most serious risks come from misuse. Swallowing DEET causes severe stomach irritation, nausea, and in large amounts can affect heart rate and blood pressure. Prolonged, heavy exposure to concentrations above 50% has been linked to insomnia, mood changes, disorientation, and in rare cases seizures or nervous system damage. These scenarios involve quantities and durations far beyond typical outdoor use. Spraying DEET into your eyes or mouth causes temporary burning that resolves with washing, though eye exposure can sometimes need treatment.
The practical takeaway: using a 30% to 50% product as directed on the label, washing it off when you come inside, and avoiding broken skin or mucous membranes keeps risk very low. There’s no safety benefit to reaching for a 100% DEET product unless you specifically need all-day coverage in extreme conditions and understand the tradeoffs.