Report: Deet, popular and potent insect repellent, is neurotoxic

Well this is bad news. I had a hunch the stuff was evil, even though I've been slathering it on like skin cream when I travel to malaria-infested places. Some 200 million people a year use the stuff, and apparently it's bad news for the brain and nervous system, particularly when combined with other repellents that have similar toxic effects. Snip from a Science Daily article:
The active ingredient in many insect repellents, deet, has been found to be toxic to the central nervous system. Researchers say that more investigations are urgently needed to confirm or dismiss any potential neurotoxicity to humans, especially when deet-based repellents are used in combination with other neurotoxic insecticides.

Vincent Corbel from the Institut de Recherche pour le Développement in Montpellier, and Bruno Lapied from the University of Angers, France, led a team of researchers who investigated the mode of action and toxicity of deet (N,N-Diethyl-3-methylbenzamide). Corbel said, "We've found that deet is not simply a behavior-modifying chemical but also inhibits the activity of a key central nervous system enzyme, acetycholinesterase, in both insects and mammals".

Popular Insect Repellent Deet Is Neurotoxic

Here's the source report: Deet inhibits cholinesterase: Evidence for inhibition of cholinesterases in insect and mammalian nervous systems by the insect repellent deet (BioMed Central)


  1. Bug sprays have always been neuro toxins I don’t know why its surprising that smearing ourselves with it is bad.

    In other news, fire can burn you.

  2. So I guess it’s time to choose your poison.. die from some insect-borne illness, or fry out your brain.

    Decisions, decisions!

  3. Instead of this rubbish, I smoke heavily whenever I see the first flying creature. Nothing comes near me. Pah! Neurotoxicity – keep it!

  4. Somehow this is appropriate coming from France where some think that radiation accumulates in the tips of beans and that’s why you snap them off. I think an important question is how much deet is actually absorbed when topically applied and whether any of it makes it to the CNS. They are using isolated mouse muscles here so if I cut myself open then yes I probably shouldn’t spray deet on the wound, that’s about all they’ve shown.

  5. that explains why my thumb was twitching by day ten of my last fishing trip!..not before or since!

  6. There really isn’t enough information in that report to come to the conclusion that we’re all going to die. Not enough there to make me stop using it to keep the deer ticks off.

  7. On the plus side, I appear to repel blackflies completely, and I don’t have the normal sensitivity to mosquito bites (so I don’t get red itchy bumps).

    On the down side, it may be that I get bitten and never notice it, and no-itchy-bumps isn’t going to save me from West Nile Virus (here) or any number of mosquito born illnesses (abroad).

    I’d always thought DEET was one of the ones that’s been suspected as dangerous for years, actually. I’m sort of surprised to hear this is new news.

    But yes, #4 is certainly right in that some information in the amount absorbed in normal use (Rather than ideal use, or worst-case use) is important.

    Obviously, spraying it on exposed muscle tissue is bad, and a fresh injury is probably bad as well. Can it be absorbed through a scab? Thin skin on the face and neck? Childrens skin? Probably through mucus membranes, so don’t lick your fingers and it’s probably best to keep it off kids and pets entirely and not handle food, because of that, but what are the ACTUAL risks?

  8. For years, I’ve been using lavender oil to repel mosquitoes. It really works! About 10 drops of oil in 2 oz. of water and spritz it all over. Plus, it actually smells good so you can go to bed without having to shower off your bug spray.

  9. Does DEET even work? Because other than a mosquito net or a steady breeze or a decent amount of smoke (campfire) I don’t think I’ve ever seen anything that actually repelled mosquitoes.

  10. This shouldn’t be hugely surprising to anyone with a good memory. When I was in school in the mid/early 90’s I remember reading science type articles (written for kids) that told the evils of the dreaded DEET. Granted, in these articles it was all about saving the birds. Deet, when sucked up by undetered mosquitoes and then eaten by birds can weaken the shells of the eggs laid by said birds. If this chemical can have that kind of effect on birds should it be any wonder that it is also bad for people?

    If the stuff is truly a health risk in the amounts and method of application used is another matter entirely.

  11. Everybody knows (or should) that you shouldn’t use it on children or pets — their skin surface area ratio to their total body weight means that they take in a disproportionately large dose…and it’s not good to smear your kids in chemicals, anyway.

    It’s also always a good idea to wash chemicals off your skin when you no longer need them, too — so once you’re back home, wash the repellant off. (it’s gooey and you don’t want it on your sheets even if it’s completely benign). If you get it in an open wound, it burns like the fires of hell itself, and you’ll waste no time at all rinsing it out, I promise.

    BUT…considering they’ve been using the stuff since 1946 (that’s over 60 years, or three generations) and no one can make any kind of a conclusive (like scientific and everything) link to health…I’ll take the risk of DEET over the risk of malaria, encephalitis, and West Nile Virus any day…and yes, people get all three of those regularly — even in the continental US of A.

  12. I keep a bottle of Repex, which is the repellent of choice for the Canadian bush (geological work). It’s 75% DEET. Works like a charm, but it removes paint, softens plastics, and numbs the lips if you smear it around your face. God help you if you get it in your eyes.

  13. as someone who has to spend a lot of time in the field, this isn’t *new* news.

    i’ve been using essential oils and they work pretty well. a few years ago i read a study by the US Forest Service and a university on how catnip oil is more effective than DEET and lasts longer (usually the only drawback to using essential oil-based repellents is how long they last).

  14. @jerril #7

    I, too, feel like this has been “known” for a while. I know my sister’s pediatrician warned against it for the little ‘uns. But maybe it was just a better-safe-than-sorry approach rather than something based on conclusive evidence.

  15. It bothers me to associate an adjective like ‘evil’ with something like DEET after a single suspect study. DEET has probably saved tens of thousands thousands of lives in malaria zones. DEET may be flawed, but ‘evil’? C’mon.

  16. Try walking in the woods of Minnesota or Maine without Deet. The stuff works. Lime infested ticks laugh at lavender oil.

  17. Doesn’t it just make sense, though? If it kills/repels little organisms, of course it’s harmful to larger ones, maybe it just takes a little more!
    That said, I’m going hiking Sunday, and I’m going to spray it on my pants legs like usual; Lyme’s disease is no joke. Of course I don’t put it directly on my skin, or breathe the overspray.
    Honestly, I can’t figure out these folks who need to “discover” or “learn” for each and every substance that, hey, it’s harmful to humans. I just assume if it’s noxious to anything, it’s harmful to me; that goes for insecticide, weed killer, anti-bacterial soap, all of it.
    Also, try the lavender oil, or the ‘Skin So Soft’, some people swear by those. Start small, break out the big guns if you have to, always use the minimum amount to achieve the desired result.

  18. This should go in the DUH pile… bug poison proven to to be toxic eh? i’m flabbergasted.

    It’s been removing the green dye off my bottles of 50 for years now! All of my camping gear has smears of green from the deet breaking down the dye found in the beer labels.

    Remember folks: never use poisons on wee kids. they’re just too little. bug poison, cough syrup, Lysol, aspartame… AVOID.

    I have lemon balm growing in my backyard. Excellent short-term bug repellent as well (1/2 hour or so).

  19. Jesus, I’m constantly amazed at how surprised people are that the toxic chemicals they put on and in their bodies are harmful!

  20. No! Not my acetylcholinesterase! I need all of the enzyme that I’ve got!

    Seriously, though, up here in the great north woods, this is disturbing news.

    And yes, Toolbag, DEET’s been effective for me: so the stuff does work.

  21. @Terra78 and Wetzel:

    Keep the Lavender Oil off young boys and girls, and possibly everyone.

    via Wikipedia:

    “Lavender oil has recently been implicated in gynecomastia, the abnormal development of breasts in young boys. Denver endocrinologist Clifford Bloch hypothesized the link after three boys presented with enlarged breasts. Subsequently, Derek Henley and Kenneth Korach of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., discovered in lavender and tea tree oil the presence of compounds which both suppress male hormones and mimic female hormones.
    Because sex hormone levels are normally low prior to puberty, young boys and girls are particularly sensitive to estrogenic and androgenic compounds. The discovery of the gynecomastia link in boys has led some researchers to suspect lavender and tea tree oils, which are present in various personal care products including shampoos and lotions, may also contribute to the increased incidence of early breast development in girls.”

  22. I also can vouch that DEET will melt through many plastics.
    I remember first hearing it was potentially dangerous in the late 80’s and quit using it then.

    I’m not sure melting plastic is a good indicator of toxicity though. Natural citrus oil will do the same.

  23. We always used Skin-So-Soft as a less stinky bug repellent, but this was before we had the internet to inform us that its utility for keeping mosquitoes away is complete bunk.

  24. Damnit! Next, they’ll be telling us that citronella candles make you vote Republican.

    Well, if it’s neurotoxicity from DEET and permanent neurological damage from West Nile Virus, I guess I’ll have to change to lavender oil and risk becoming a pretty, pretty princess.

  25. I use a 100% pure DEET spray in a pump bottle so that my future grandchildren will not be bothered by mosquitoes.

    SRSLY though–it does work. But I never put it on mys skin: cuffs and collars of a shirt has always worked just fine, even for big bastard bugs that bash against the side of the tent calling come out and plaaay-aaayy!

  26. Xeni, for someone who purports to be a technology reporter, you ought to know that one study doesn’t mean the product is toxic.

    It could be a lot like saccharine. Yeah, if you consume it in ridiculous quantities, it might be toxic. However, it’s possible that judicious use is probably better than not using it.

    This is a non-story.

  27. Though this may be an important finding with respect to some interactions, such as using DEET with other drugs that may affect acetylcholinesterase levels, such as say, anti-nerve gas treatments given to troops in combat, who are also using DEET repellants (both were widely used in the Gulf war together)

  28. My parents have forbid me from using deet except in extreme circumstances (certain malarial death) since I was very very young. Is it new information that it’s toxic? I always thought it was.

  29. Article in Science Daily = Press release. (Not saying there is anything wrong with that, its my bread and butter. It is just something you should know.)

    I remember a study from a few years back that found excessive deet use correlated with memory problems in park rangers in the Everglades. However, those were people who used it every day in large quantities.

    As with all things, the dose makes the poison.

  30. re #14 a minor point, but DEET’s anti-mosquito action isn’t as a poison. In simple terms, DEET keeps mosquitos away because they just don’t like the smell of it. It’s a repellent, not an insecticide (as any kid who’s doused a mosquito in DEET and wondered why it didn’t immediately die knows).

  31. Toxic chemicals are bad. Malaria is worse. And in another ten years we’ll probably be seeing sensationalized news reports calling lavender oil “the silent killer.”

    If you’re not at major risk for insect-born illness but want to avoid the little beasties I find that eating a lot of garlic before hiking seems to work pretty well. Of course the bugs might not be the only thing that will be repelled by your scent.

  32. I’ve read there’s an oil in catnip that’s more effective than deet. The article didn’t specify how toxic it is.

  33. re # 26. actually from what i have read it is not the smell but as the mosquito heads toward the warm body temperature the closer they get the deet tweaks their nervous system (obvious clue there why it’s a neurotoxin) into thinking the warm blood is in the opposite direction. hence you will see a lot of mosquitos going back and forth, closer and farther near you like they can’t make up their mind.

    put the deet on your cloths and not your skin and forget about it.

  34. @ Altwolf. That Wikipedia article has the same inaccuracies pointed out in this article about DEET. The link between the gynecomastia in the boys was not conclusively proven to be caused by the beauty products in which both tea tree and lavender were blamed for the gynecomastia. Robert Tisserand explains the holes in this report better than I ever could. But that one scientist hypothesizes a connection between lavender & tea tree oil and gynecomastia, and then researchers present a paper showing the endocrine disruption of pure lavender oil and pure tea tree oil (not the products in question), no in vivo tests are done, and we never learn the name of the beauty products in question… huh. What about hormones in dairy products, or endocrine disruptors in plastics? I’ll take my chances with lavender over DEET any day.

    But, truth be told, catnip essential oil (which actually can be neurotoxic if used in large doses) works better than DEET or lavender oil: .

  35. When I travel I use Tea Tree Oil. It keeps the bugs at bay and can also be used to sterilize wounds, or bites if one does get through. Good stuff, it has done right by me in tropical jungles while others got eaten up.

  36. Toolbag @9:

    DEET works incredibly well for keeping the Minnesota state bird off your back.

    Mosquitos are so overly attracted to me that, when sitting in a group of people, NO ONE ELSE gets bit. NO ONE. Spray some DEET on me and everyone else gets bit. Mwahhahhahh!!

    Probably a good thing that I only use the stuff sparingly at harvest time when wearing a sweatshirt (hood up and sinched like Kenny) and jeans isn’t enough protection.

  37. Altolf: Interesting… So all those old-time “swishers” were actually onto something chemical, with their preferences for lavender this, and lavender that. Welly, welly, well.

  38. Avon’s Skin-So-Soft lotion is 100% effective at repelling mosquitoes & biting flies. Granted, you have to apply it to all exposed skin, and it doesn’t wash off easily. But it’s just lotion. If you don’t mind smelling like a girl all day, then I recommend using this.

  39. Eh…it’s a halfway decent inhibitor in vitro. 500uM isn’t a horrible inhibitor, but it’s not great, either. 500nM, I’d be impressed and a little concerned. Even 1uM, as they report in insects, I’d be cautious.

    But given the high Ki and the lack of people hospitalized with severe convulsions after accidental high DEET exposure, I’ll keep on using it for now. Unless this stuff can somehow just zip through the skin, it’s not going to have much of an effect. Even then, it would probably take a few mLs of the 100% stuff to get to an effective dose. Unless you’re a kid….kids should probably avoid the stuff. But that’s been a recommendation for years.

    Mammalian in vivo, please. Then we’ll talk. Interesting paper, though.

    Chris Spurgeon: This paper presents data that suggest it is in fact toxic to mosquitoes via the feet at concentrations similar to what is found on human skin after application.

    Lex, nehpetse, carriem, others : that was probably the solvent carrier (acetone, I’d guess), and probably not the DEET that dissolved your pen/took off the green dye/etc. DEET is practically insoluble in water (low millimolar, tops), and they usually use an organic solvent to dissolve the stuff. 100% here is w/v, and doesn’t mean that the stuff is 100% DEET by volume. It means 100g of DEET/100mL of solvent.

    Frankieboy: No, that does not stand to reason. Different organisms have distinct metabolisms. The more further removed, the greater the difference. We can (and do) target these differences. That’s the problem with these studies; once you get to crazy-high concentrations (and 500uM borders on crazy-high) they will start hitting other things. The dose makes the poison. Enough organic hand squeezed orange juice will kill you.

  40. So deet is a neurotoxin and can melt plastic – and it’s marijuana that’s still illegal?

    Well, at least I know I can still get safe drinkable water from a plastic bottle… wait, damn it!!!

  41. I had a bottle of 100% DEET leak in my van years ago and it softened the plastic to the consistancy of used chewing gum in just a few hours. 6 years later when I sold the van, it was still soft enough that you could push the plastic around with your finger tip. I also had a set of eyeglass frames ruined (also plastic) from contact with DEET that I had applied to my face. I try to avoid using it now but sadly, there’s nothing that will stop bugs as well as DEET. (Sorry, not even Skin-so-soft or Absorbine jr. will stop Minnesota skeeters, they treat both as condiments.)

  42. What about picaridin? That seems to be a popular alternative. I have to use something… I attract mosquitoes like a magnet and my bug bites are super huge scary sized with huge helpings of itch.

  43. Y’know, when they do laboratory tests of new drugs that come out looking fine, they still test them on people first. Because you can juice up the mice (or mosquitos, I suppose) all you like, but you won’t really know what it does to humans until you test it on an awful lot of humans.

    We’ve used DEET for years on an awful lot of humans. Looks like we’re doing okay.
    Of course, doing a multi-year study of a large human population is expensive, and I guess this guy’s grant only stretched so far…

  44. I’m surprised this is news. Or perhaps, the news is that someone’s still looking at it. I’ve known it was neurotoxic for years.

    10 years ago, I learned that anything more than 30% DEET is neurotoxic. Those old 100% DEET army repellents would melt plastic pretty nicely.

    Nowdays, it’s rare to see anything more than 15%.

    As for the toxin part, I can testify that getting DEET into your eyes or mouth (through sweat) can make you pretty dizzy and uncomfortable. It’s also quite bitter. So yes, it’s neurotoxic.

    One great solution for your head (although it looks dorky) is a mosquito veil. No toxins, it keeps the bugs away from your head (if you wear a hat), it costs as much as 3 tubes of DEET, and lasts for at least a decade. I still use low-concentration DEET on my skin and clothes, especially if I’m not planning to sweat much, but that’s simply because I don’t think there’s a non-toxic and effective bug repellent out there, and DEET works if you use it knowledgeably.

  45. When I was a treeplanter in Northern Ontario, I would spray deet on my hard hard to keep the black flies away. It was when the deet started eating through the plastic of the hard hat that I knew it was some potent and toxic shit.

  46. Gotta laugh here and shout, “Toja!” I must be hyper sensitive to these nasty chemicals, a reverse tolerance kind of thing, because every day the Clorox Clean-Up smells worse and worse to me. People slather cream, polish, spray, antibacterial, everything they can get their grubby hands on all over themselves. I just know all of this stuff is killing us. Smell a rose or a bud of cannabis — everything else is an abomination, and you are paying for it with the destruction of your mind. I firmly believe that Most medical conditions are largely brought on by the pollutants in our environment. If our grandkids survive, they’ll ask, “What on Earth were those idiots spraying?!?!”

    (Captcha poetry: “Hadeff’s Aversion” … the acute recoiling from brain-destroying pollutants!)

  47. This study was done on cell cultures. It is not really applicable to entire animals with complex structures. A layer of dead skin cells is a considerable barrier. Most commercial (at least those in the USA) DEET products are delivered in a mixed solvent system that reduces skin permeability. Ethanol *only* as a carrier does seem increase permeation.

    I will continue to use 100% DEET for camping in areas with considerable (say, 1/bite minute) mosquito density.

  48. “Herbal Armor” works very well. Plus it makes your whole body buzz a little bit. It’s not a euphamism for pot, either. Just a lovely, all natural DEET-free mosquito repellant. I think its the peppermint oil that gives ya that special tingly sensation.

  49. Anecdote is not the singular of data, I know, but I was on a group trip in Central America several years ago with a young woman who was obsessed with keeping the bugs away. She applied and reapplied repellant all day, every day, and then towards the end of the ten day trip developed a toxic reaction that killed her.

    We thought she was overdoing it, but we had no idea she was poisoning herself to death.

  50. My brother had his first known epileptic seizure ~20 years ago on a camping trip and one of the things they looked at extensively then was the use of a DEET based repellent. They could never tell us conclusively what caused his first seizures, but we were told that DEET could cause seizures, abnormal brain activity, and have various side effects from extended use – especially in combination with other chemicals.

    That was over 20 years ago…

  51. One solitary report looking at one alleged lavender oil does not constitute a “study” of lavender oil or a definitive conclusion. The fact is that there is no conclusive evidence that lavender is problematic for humans.

    Lavender has been used by millions of people around the world for centuries and there has never been any record of or indication of any kind that it is responsible for any problems in humans. On the contrary, a search of PubMed shows a host of studies verifying Lavender’s healthful properties — including its anti-cancer benefits.

    Humans evolved alongside plants. Indeed, plants are food/fuel for our bodies and our DNA dictates that our organ systems have the ability to recognize/utilize and process/metabolize botanicals and their naturally-occurring constituents.

    Conversely, the fairly recent rise in fertility and reproductive system problems, incidences of cancer, immune disorders and neurological disorders, however, can be correlated to the increased use of a vast array of man-made petrochemical substances introduced over the past five decades.

  52. Comment #32 by klenow should be required reading. If anybody skipped over it, I strongly recommend going back to it.

  53. When I was in the Military I got in trouble for bringing my own bottle of 97% Deet to basic training, because it was a known neurotoxin.

    They proved this to me by spraying it on chemical weapon detector paper, which promptly turned bright blue, indicating the presence of a neurotoxin.

    This was 8 years ago. How is this news?

  54. Xeni, Avon’s Skin so Soft works great to keep bugs away. Used it in Hawaii and never had a bug bite.

  55. Thank you Klenow, good stuff. Of course, It makes much more sense for the solvent to destroy our stuff than the toxin. (Not as sexy tho!)

    I will still equate green smears with bugless toxin, however. It’s a lifetime’s worth of conditioning, you understand.

  56. Who’d have thought that a chemical which kills bugs (DEET is also used to kill bugs by exterminators) by disrupting their neurotransmitters (think of it like insect sarin) would do things like mess with human CNS when they covered their skin in the stuff?

  57. For me, it’s a question of the level of risk I’m willing to accept. Which risk is more likely: the risk of contracting malaria in a tropical region, or the risk of being poisoned by insect repellent? Which risk has more serious long-term consequences? I haven’t done the research on this one, but I would guess malaria is the greater risk.

  58. @42 Veritaz:
    This is a false distinction: there’s a lot of overlap between what you get from plants and petrochemicals. And a lot of things from plants are truly nasty, like coniine, strychnine, or even hypericin.

    You’re probably right that one study isn’t good enough to show lavender oil is harmful, but then you should apply the same level of skepticism to one study about DEET.

    In both cases, dose is probably key. Lavender wouldn’t be the first pleasant plant fragrance that turns out to be toxic if you concentrate it well beyond natural levels. Thujone, for instance.

  59. Using OFF makes my skin hot after 10-20 minutes. Not like a burning, itching allergic reaction, but it feels hot like I’m in the direct sun even if I’m in a cool shade. It’s really strange. Of course I don’t know if it’s the DEET, the solvent, or some other ingredient.

  60. Whoa klenow! Enzyme kinetics are not any kind of measure of the toxicity, or safety, of a product. I’m a biochemist myself and I am not in the slightest reassured by your comment. More to the point is how well it is absorbed by the skin. As a general rule, it should be assumed that *everything* put on the skin is absorbed, unless proven otherwise. The cavalier attitude that people have about lotions and cosmetics is completely unwarranted. I also predict that we are going to start hearing bad things about sun screens. I use these kinds of products as little as possible.

  61. DEET itself is a solvent. I’ve got a little pump bottle of 98.11% DEET handy right now, though I only use it sparingly. A little on the clothes goes a long way. No need to put it on your skin.

  62. I’m sorry and all, but I have never found anything else that works as well as 100% DEET. And I greatly enjoy not being eaten alive. I grew up slathering myself with it all the time.

  63. I first used DEET in the mid-80s and even then I was already informed (through some of my military connections) that the stuff is not innocent. Back in them days I was told something vague about possible cancer risks and, like the article states, risks concerning the central nervous system. Nobody really knew the finer details, and the internet wasn’t common good so finding any real data was impossible.

    The warnings stuck, though, and I’ve used the stuff only a few times. And had to wonder whether it really worked because I got stung as much as when I hadn’t used anything. Sitting around a smoky fire with a little draft around the ankles works much better.

  64. DEET itself is a highly effective solvent- hence the reason it will chew on plastics so handily. As one of its names implies (N,N-Diethyl-meta-toluamide), it is based on a toluene molecule. I remember one particular story from the 1980s when the keyboard of a portable computer (yes, they had them then) started to melt from the DEET on the fingertips of the user.

  65. @42- “Humans evolved alongside plants. Indeed, plants are food/fuel for our bodies and our DNA dictates that our organ systems have the ability to recognize/utilize and process/metabolize botanicals and their naturally-occurring constituents.”

    Y’mean like poison ivy? Holly berries? Rhubarb leaves? Aconite? Nightshade? The friendly castor bean? Oleander? It’d be good for you to note that the plants we were evolving with were trying to evolve into things that didn’t get eaten by roving mammals. Natural doesn’t automatically mean good– nature’s generally out to kill things that eat it.

  66. “Nowdays, it’s rare to see anything more than 15%. ”

    #38 – Are you in the US? Have you been in an outdoor store recently? Ben’s 100 and Repel 100 are both incredibly popular, and they are both over 98% DEET. They also have 30% and 40% varieties that are very popular.

    I use Ben’s 100 regularly, and it is the most effective treatment I know of, however, there are some places where the blackflies and mosquitoes seem to enjoy it….at which point the no-see-um head-net comes out.

  67. I’ve always hated this stuff (you’re not supposed to get it on certain fabrics, because it MELTS them!!), but at the same time it was the only repellent that was truly effective. I once passed a guy on the Long Trail in VT, we were both one day out on a long hike, he was using some all-natural repellent and was setting up his tent just so he could relax and eat lunch. Several days later I met him farther up the trail and he was covered head to toe in black fly bites– it looked like he had chicken pox. He ditched the all-natural stuff, said it was “like BBQ sauce for the bugs.”

    I was talking out of my ass, I jumped before I looked, and I made some wrong assumptions. Fortunately for my ego, I did say “probably” several times in the above post.

    1) I got curious, so I did a little searching for what the carriers of DEET would be. In that search, I saw a picture of its structure and I’ll be damned if that’s not one hell of a solvent. Based on the structure…that puppy will dissolve a lot of stuff. Not quite acetone level solvent, but a strong one. And, because I learned my lesson, I did look it up…and yes, it is characterized as a strong solvent. This is most likely what happened with the poster that got it in his eyes & it burned.

    2) Also, unlike most pharmacueticals, DEET concentration IS reported as v/v and not w/v, so 100% DEET is in fact pure DEET.

    3) There have been sporadic reports of DEET toxicity through the years, but they seem to be exceptionally rare. I could only find a few cases. It’s probably bad to get this on your mucus membranes or open wounds, but chemically speaking, intact skin is tough stuff.

    I still stand by the claim that this study isn’t very scary. Except for the insect stuff, the studies were in vitro and at very high concentrations. It’s possibly suggestive, but you’d really need to slam yourself with the stuff to have any effect.

    The solvent part doesn’t really bother me much, either. We don’t really use enough to have an impact. I for one will continue using DEET based bug spray.

    also…noticed above from veritaz…

    “Humans evolved alongside plants. Indeed, plants are food/fuel for our bodies and our DNA dictates that our organ systems have the ability to recognize/utilize and process/metabolize botanicals and their naturally-occurring constituents.”

    Plants did not evolve to become our food. Plants evolved to make more plants. We (and many other things) have evolved to use plants as food. And the plants evolved further to keep their important parts from being eaten.

    Most of the botanicals that we use are actually defensive chemicals the plants make to protect them from parasites and other things that eat them.

    What is natural is not necessarily good. Foxglove, hemlock, nightshades, anything with thorns, poison ivy & the like are just a few examples. These are plants that have evolved mechanisms to keep herbivores & omnivores away, or select for the animal of choice. In a way it’s good…good for the plant. Which often means bad for things that want to use the plant.

    The reason there are good botanicals for keeping mosquitoes away is because plants have also co-evolved with mosquitoes…mosquitoes use our blood for eggs, but they feed on plants. So, some plants have evolved mechanisms to keep the bugs away.

    Ok, I could go on for pages on this, so I’ll stop. Let me just sum it up with two take home points:

    1) That which is natural is not necessarily good.
    2) The dose makes the poison.

    As an archetype example, look up cyanide in apples, snopes has a good article on it, IIRC.

  69. I’ve been using lemon eucalyptus oil. It doesn’t work, but it smells like rotting fruit, so yay. As a child, I used Woodsman Fly Dope, which also protects from human-borne illnesses because nobody will get with fifty feet of you when you wear it.

    I counted 53 mosquito bites in a single night in India and I didn’t get any diseases, so I’m not terribly worried about contracting a mosquito-borne illness in California. It’s that buzzing that drives me nuts. That annoying buzzing that only starts when you turn off the light and stops the minute that you jump out of bed and start flailing around the room trying to kill the little motherfucker.

  70. @80: Gotta keep up the harassment (: klenow:

    Ahem: “Plants did not evolve to become our food. Plants evolved to make more plants. We (and many other things) have evolved to use plants as food. And the plants evolved further to keep their important parts from being eaten.”

    Um, if you look at what plants are the most common now, they’re ones that are edible by humans. Plants evolved to make more plants, and sometimes that involves being eaten. The grass family is the best example of this one. They have leaves that grow from the base, so the tips can be eaten over and over by grazers. Other plants that have growing parts further out where they get eaten, so they die from repeated grazing, and the grass ends up winning by surviving the assault.

    Bottom line: don’t underestimate the cleverness of plants. They play to win on their own terms. Sometimes they work with us, sometimes not.

    @81: Lucky you. My partner’s niece gets blisters from mosquitos bites, so sucking it up and dealing isn’t an option for her. People vary tremendously both in their attractiveness to blood suckers and in their response to the bites. I still prefer a mosquito veil, but DEET, intelligently used, works okay.

    Also, you could just use mud to keep off the bugs. Unlike those products you’re smearing on your skin, it’s free, and if you pick the right mud-pit, it’s non-toxic and not too stinky either.

  71. it may very well be toxic but the real question is whether or not the doses we encounter in every day use are enough to actually cause harm. As an analogy, think of the moon hoax loonies (pun intended) out there who talk about the van allen belts. While it is true the radiation from space may kill you eventually, in small doses it is likely harmless.

  72. This has to be put in context. First, it is prudent to use in situations where the risk of acquiring serious infectious disease from insect vectors is high. In areas where malaria, dengue, leishmaniasis, and lyme disease, etc. are endemic, the potential for injury from these diseases is far greater than from the neurotoxicity of DEET. Limiting exposure to DEET is important, but so is avoiding these illnesses. If you’re somewhere without endemic insect vectored diseases, then fine, use citronella, but it’s just not effective enough.

    Secondly, there are different kinds of neurotoxins. DEET acts as an acetylcholinesterase inhibitor. ACh inhibitors are neurotoxic in that they inhibit normal nerve cell communication– it’s how most nerve gases and many insecticides work. However, they don’t cause nerve cell death. The dosage from DEET, if used carefully and not directly on skin is relatively safe– it’s far better than getting CNS damage, arthritis, hemorrhagic fever, disfiguring leishmania or other problems.

  73. @Antinous:

    “I counted 53 mosquito bites in a single night in India and I didn’t get any diseases, so I’m not terribly worried about contracting a mosquito-borne illness in California.”

    Since I assume you’ve crossed many more than 53 streets without getting run over, you probably just close your eyes and step off the curb nowadays, right?

    Anecdote is not data.

    West Nile virus has been in California for years. Since 2004, there have been 2,672 cases in humans in California, 91 of which have been fatal.

    Last year alone, more than 2,500 dead birds tested positive for West Nile.

    So far in 2009, 34 counties in California have recorded West Nile activity.

    1. Since 2004, there have been 2,672 cases in humans in California, 91 of which have been fatal.

      As of this week, there have only been five reported cases in California in 2009. I’ll continue my regimen of not worrying.

      To fight the bug, we must understand the bug. We can ill afford another Klendathu.

  74. pah. ethylmethylphosphonylthioate. There’s a compound that actually attacks your acetylcholinesterase enzymes, DEET’s a walk in the park.

  75. “Um, if you look at what plants are the most common now, they’re ones that are edible by humans.”


    I highly doubt that. I don’t have numbers, but that does put our claims on equal footing.

    And I did say “the parts they don’t want eaten.” It is very important for a plant to have the seed bearing part eaten and the rest left alone; thorned berry plants are a great example of this.

    Bottom line (again): What is natural is not necessarily good.

    Anonymous #70: I’m a biochemist, too. They are claiming that the inhibitory effect on AcHE is the source of the toxicity. Therefore, kinetics does give us a floor value to the toxicity. So yes, it is relevant. And it does most likely stay on the skin; it’s only minimally soluble in water. Hell, if you read the paper they had to use DMSO & acetone to do their assays (it was properly controlled though, I’m not saying the effects aren’t real).

    Bottom line : You should recall from your basic tox & pharm classes that the dose makes the poison. Yes, this stuff has an effect at 500uM. But is that really physiologically relevant?

    Especially taking into account that it’s been in heavy use for nearly 50 years, and the only deaths have been suicides or very young children that use way too much. The side effects reported are mild or due to accidentally getting it in the eyes. Source:

    This is a kinetic study in search of clinical application. We’ve all at least thought about it.

    I’m not saying that I’m 100% certain DEET is 100% safe. Only the ignorant would say that about any compound. I’m just saying that this study does not convince me that DEET is a potent neurotoxin.

  76. Indeed, the post is sensationalist and doesn’t serve the cause of science. Let’s hope people who promulgate public policy will wait until the scientific process plays out, and further studies and investigations are conducted, particularly with regard to how this finding relates to how people actually use actual repellents that contain actual proportions of DEET used in the actual world.

  77. #88,

    I just hope you don’t advocate that people visiting India, where you allegedly received 53 bites with no effect, have a similarly cavalier attitude, given the thousands who die from mosquito-borne diseases there every year.

    The point is not to panic, nor to engage in the hyperbole this alarmist post engages in based on a single study. Science doesn’t work that way. At best, this study calls for further study.

    The point is to rely on data, rather than personal anecdote, when it comes to public health policy, and not to draw conclusions about what it or is not safe based on happenstance.

    Risk is a matter of percentages, not absolutes, and intelligent behavior, as well as intelligent policy, should be based on understanding and assessing the odds, not based on the logic “I haven’t been hit by a car yet, so I don’t need to take reasonable precautions” – any more than “I read that people get hit by cars, I better stop walking”.

  78. @82 Heteromeles:
    Um, if you look at what plants are the most common now, they’re ones that are edible by humans.

    Inside the city where I live, at least, the most common plants are probably grasses, but not the sort any humans would eat. There are large fields of those in the surrounding countryside, but there are also large areas mainly covered by wind-spread trees, which I think just about balance one another.

    All in all, I would guess the most common genera are spruce, aspen, and maybe wheat. A single species of the last may be more common than any other single species of the others, but I’m not really sure.

    In any case, even if the most common species are the ones we can eat, it’s pretty clear the majority of plants out there still aren’t trying to get us to munch on them.

  79. ALL man-made chemical substances must be suspect, because their manufacturers are unconcerned with how they fit into the ecology of natural chemicals … of which we are all made.

    Indeed, the word ‘toxin’ in most news reports almost invariably involves man-made substances. We are apparently blinded to this fact.

  80. #40 posted by Anonymous:

    Where are the old Mr. Yuk stickers when you need them?

    I have a Mr. Yuk tee-shirt.

    You may touch me.

  81. Again, for the reading (or thinking) impaired:

    DEET was not used as a mosquito repellent because it KILLED mosquitos, but because it repelled them.

    Similarly, bear repellent and shark repellent do not kill bears or sharks when sprayed upon them.

    The neurotoxicity of DEET in insects is part of the results of the research.

    Thus, there was no particular reason to suspect that DEET was harmful to humans, because it was NOT USED to kill insects.

    Secondly, the fact that something melts plastic does not indicate that it is toxic. I have in my possession non-toxic plastic cement. Its PURPOSE is to melt plastic. Specifically, to melt the arms of little army men to the torsos of little army men. It is NONTOXIC. Its remarkable efficacy at melting plastic does not make it POISON.

    Please stop being dumb.

  82. Personally, I like the smell of DEET. Mus’ be from camping trips… Tastes terrible.

    I’ll second the recommendations to put it on clothes preferentially. And any skin covered by clothes doesn’t need sunscreen (which I feel just interferes with my sweating– I’m cooler in light pants than in shorts and sunscreen). Important point– I’ve been bitten through light clothing before. And spraying it on a hat is a lot less sticky than getting it on your face.

  83. …and for the hard of reasoning, I’ll repeat

    DEET is so poisonous it melts plastic! anything that melts plastic has got to be toxic. We’ve known for years that DEET must be harmful because it kills insects.

  84. If you think Malaria and West Nile are bad, check out my least favourite mosquito borne disease … Japanese Encephalitis.

    And there are others. How about Dengue Fever?

    All of them are far worse than a little DEET on the skin.

  85. #63 posted by Anonymous, August 7, 2009 11:18 AM
    “When I was in the Military I got in trouble for bringing my own bottle of 97% Deet to basic training, because it was a known neurotoxin.
    They proved this to me by spraying it on chemical weapon detector paper, which promptly turned bright blue, indicating the presence of a neurotoxin.
    This was 8 years ago. How is this news?”

    And yet the military still uses Deet on it’s soldiers, equipment, and even goes as far to treat their soldiers’ uniforms with Deet for those deploying to the middle-east since the start of the Global Farce on Terror. Irony?

  86. Forget AMBIAN parties…

    It’s now cool to have DEET gatherings (Since 1950).

    What was BZ made from?

    … Just drink the COOL AID!

    – Brought to you from The Behavioral Modification Company (DARPA).

  87. @ #87 posted by klenow

    For the most part I agree with you – you do seem to know what you’re talking about. But:

    “And it does most likely stay on the skin; it’s only minimally soluble in water.”

    Being minimally water soluble is good for keeping it from being sweated off into your eyes or mouth, but what about dermal absorption? A substance is more likely to absorb through cell membranes if it’s hydrophobic than if it’s hydrophilic.

    That said, I’m still going to use DEET. The dose makes the poison, after all.

  88. Researchers say that more investigations are urgently needed to confirm or dismiss any potential neurotoxicity to humans…

    But yet they say deet IS neurotoxic.

    So why urgently request more research?

  89. Mouse AChE inhibitor does not equal in vitro human AChe inhibitor does not equal human topical neurotoxin.

    The study finds that Deet is a potential neurotoxin, and potentially has synergistic toxic effects with carbamate insecticides.

    More research is required to see if the potential effect is ever realised. For example, does Deet penetrate human nerve cells when applied topicaly?

  90. I remember there was a big scare in the early – mid 90’s about deet. I thought it was pretty much common knowledge that you spray it on your clothes, not on your skin.

  91. Keep your hands off of my acetylcholinesterase, you bastards!

    Also, the article misspells “acetylcholinesterase”

  92. I have used Deet for many years. I am a male, 56, and suddenly, in the last week (!), I get a sudden burning sensation after I apply it, similar to that described here by “DCULBERSON” on August 7, 2009.

    I have tried two different preparations, one a drugtore brand (Walgreens) aerosol spray, 23% Deet, and Deep Woods Off pump spray, 25% Deet. The reaction is the same with either, an annoying burning sensation on the skin a few minutes after application. The sensation is located wherever the stuff was applied. Seems worse on my arms than my legs.

    This is pretty annoying, and taking a shower is soothing, but it does not “wash off” the effects of the sprays. I just have had to wait until the sensation subsides.

    I am hoping that I have not become hyper-sensitive to Deet, but only time will tell.

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