DEET and Picaridin Work. They Are Still Not a Barrier.

Let us start where the honest critics of the mosquito aisle usually get it wrong. DEET works. Picaridin works. Anyone who tells you otherwise is selling you something, and we said we would not be polite about that.

The best comparative data still comes from Fradin and Day, who tested sixteen products on fifteen volunteers and published the results in the New England Journal of Medicine in 2002. A spray containing 23.8 percent DEET kept mosquitoes off the skin for an average of 301 minutes, just over five hours, and ranked higher than everything else in the study. By contrast, the citronella products protected for twenty minutes or less, and the impregnated wristbands lasted around twelve minutes, which is no meaningful protection at all. That is the difference between a repellent that does its job and a candle that mostly buys you ambience.

Picaridin belongs in the same "it works" column. It is registered by the United States Environmental Protection Agency and recommended by the Centers for Disease Control and Prevention, and at matched concentrations it performs comparably to DEET. So this is not an article about snake oil. Repellents are not snake oil. They are effective tools, and they have a real, legitimate role.

So what is the problem?

The problem is not the chemistry. It is the story that gets told around it.

Look closely at that five-hour figure. It is the ceiling, measured on a still forearm in a cage, and it is a countdown. Fradin and Day also found that a spray with only 4.75 percent DEET lasted 88 minutes, and that lower-concentration products can fade in an hour or two. Protection does not simply stop being reliable at some published hour. It stops the moment the film on your skin thins out, and it stops completely the moment you forget to reapply. The active ingredient is doing exactly what the label promises. The failure mode is human. You are hot, you are busy, the evening runs long, and the reapplication that the label quietly depends on never happens. That is not a laboratory failure. It is the ordinary way a real evening goes.

Then there is what the repellent leaves behind. A skin repellent is, by design, a chemical film you wear. It sits on your arms and legs, it transfers to clothing and bedding, and it is reapplied through the day. Used as directed, EPA-registered repellents are considered safe, including for pregnant and breastfeeding women. That is worth saying plainly, because fearmongering about repellents is its own kind of dishonesty. But "safe when used as directed" is not the same as "nothing to think about". Direct, repeated skin contact and residue are a genuine trade-off, and a household that reaches for the spray a dozen times a day is carrying more of that trade-off than the label conversation usually admits. It is the same lesson the aisle refuses to learn elsewhere: burning a single mosquito coil indoors can release fine particulate matter equivalent to dozens of cigarettes. What you put on your skin, and what you burn in the room, is never simply free.

Effective, but not a barrier

Here is the sentence the aisle keeps blurring. A repellent is a supplement, not a barrier, and not a system.

It is sold, too often, as complete protection: one bottle, problem solved. It is not. A repellent does not cover the baby asleep in the next room. It does not hold a line across an open window while the family watches television. It does not work while you sleep unless you are willing to coat your skin and reapply through the night, which almost nobody does and no one should have to. A spray protects the person wearing it, for as long as the film lasts, as long as they remember. That is a supplement to protection, not the whole of it.

The mode of action that medicine keeps returning to is the physical barrier: a mesh between human and mosquito, with nothing to inhale and no residue on the skin. A correctly rated net protects a bed, a balcony, or a garden enclosure for years, not hours, and it does not depend on anyone remembering anything. It works while you sleep. This is exactly why we sell an untreated range as well as a treated one, the treated line reinforced with permethrin under EU BPR authorisation (permethrin, EU-0026815-0000): a well made, intact, correctly used barrier is real protection whether or not it carries an active ingredient. The failure the aisle hides is the wrong mesh, poor durability and no certification, not the absence of chemistry.

None of this is a reason to panic. Mosquitoes are the deadliest animal on earth, and vector-borne diseases still cause well over seven hundred thousand deaths a year, the great majority through malaria, with dengue also fatal. Chikungunya, by contrast, is often disabling but rarely fatal. Those stakes are exactly why honesty about protection matters more than a scary sentence: the goal is to help you protect the people you love, not to frighten you into a purchase.

So keep the DEET or the picaridin. They earn their place in a rucksack, on a trail, on a summer evening in the garden. Use the concentration that suits the exposure, follow the label, and reapply. Just do not mistake the bottle for the whole defence. Put the barrier first, at the bed and the window and the door, and let the repellent do the honest job it is genuinely good at: covering you for the stretch when no barrier can.

Sources: Fradin and Day, comparative efficacy of insect repellents, NEJM 2002 | CDC, prevent mosquito bites (repellent safety and recommended active ingredients) | WHO, vector-borne diseases fact sheet | ECHA biocidal products register (EU BPR authorisation EU-0026815-0000) | Liu et al., mosquito coil emissions and health implications, EHP 2003

Medical disclaimer: this article is general information, not medical advice. For guidance on disease risk, pregnancy, infants, or specific health conditions, consult a qualified healthcare professional.