DEET is the gold standard for insect repellent. I’ve covered it fairly extensively at the Bug Blog–it’s the best thing we have to prevent a wide spectrum of insects from biting and transmitting an even wider spectrum of diseases.

Some new DEET research was published this month, and the media…well, has done a crappy job of covering it.  Here’s the latest headline:  Insect Repellent DEET is Neurotoxic.

One thing all the news stories have in common is a very alarmist tone, and reprinting freely from a press release that has very little connection to the reality of the paper.  When you look at the research, they did NOT find that DEET is neurotoxic, and it does NOT cause nerve damage.

Here’s the take home:

If you decide not to use DEET insect repellent on the basis of this bad journalism, you are probably putting yourself in danger. DEET is really the only repellent we have that can deal with ticks, and also protects against a wide range of biting flies.

The results in this paper are preliminary, need to be confirmed, and even IF confirmed, remain irrelevant to the average person who might want to use DEET.

Right, that’s the message.
Now to the details.

Here is what the researchers ACTUALLY found:

Corbel, V., Stankiewicz, M., Pennetier, C., Fournier, D., Stojan, J., Girard, E., Dimitrov, M., Molgo, J., Hougard, J., & Lapied, B. (2009). Evidence for inhibition of cholinesterases in insect and mammalian nervous systems by the insect repellent deet BMC Biology, 7 (1) DOI: 10.1186/1741-7007-7-47

“electrophysiological studies were performed on isolated mouse phrenic hemidiaphragm muscles. We showed that 500 µM deet prolonged by about threefold the decay time constant of synaptic potentials on endplate regions of the muscle fibre…”

Wha? Ah.
Here’s a translation into English (by me):

We put DEET directly onto mouse cells and insect neurons in test tubes. It had a mild inhibitory effect on an important enzyme. The amount of DEET we used on mouse cells was 500 times the level that was active for insect cells. The amounts we used were several orders of magnitude larger than you would ever encounter in life as a human user of DEET repellent.

The best breakdown of this story I’ve seen yet was at Neuroskeptic. In fact, Neuroskeptic saved me a whole lot of time and work by writing an excellent article that I will now swipe here and quote freely:

“the fact that DEET can act as a cholinesterase inhibitor in the lab changes nothing. It’s still safe, at least until evidence comes along that it actually causes harm in people who use it. You can’t show that something is harmful by doing an experiment showing how it could be harmful in theory.”

This paper, when combined with decades of DEET usage data with very, very few adverse affects reported, is really not news at all.  It’s interesting, sure. But it’s not at all relevant to the average American trying not to be bitten while BBQing.

I also agree with this statement from Neuroskeptic:

“To be fair, there is one cause for concern in the paper – in the experiments, DEET interacted with other cholinesterase inhibitors, leading to an amplified effect. That suggests that DEET could become toxic in combination with cholinesterase inhibitor insecticides, but again, the risk is theoretical.”

In some situations, DEET is combined with other compounds that it could, potentially, interact with–but that almost never happens in the US. Those situations are more common in military and tropical uses.  This is a good note to be careful, and to monitor that in the future.  There is also some (laboratory) evidence that sunscreen can increase absorption of DEET, and the two should be combined with caution.

If you are using DEET sensibly, you have nothing to worry about.
What is sensible DEET use? Borrowing from The American Pediatric Society, as well as my own experience:

  • Do not use DEET under clothing. Put it ON your clothing.
  • Do not use DEET on the hands of young children; avoid applying to areas around the eyes and mouth.
  • Do not use DEET over cuts, wounds or irritated skin. Wash treated skin with soap and water after returning indoors; wash treated clothing.
  • Avoid spraying in enclosed areas; do not use DEET near food.
  • 20% DEET is enough for nearly all US situations. You can buy higher concentrations, but don’t.
  • Don’t spray DEET on spandex (it’s a long story, but trust me. This won’t end well for you)
  • Don’t drink, smoke, or otherwise do butt-stupid things with DEET. It’s safe, but only if you play by the rules.
  • Posted by Gwen Pearson

    Writer. Nerd. Insect Evangelist. Have you heard the good news? BUGS!


    1. Also, don’t spray DEET near electronics or anything with a lens.

    2. I have a bit of a skin reaction to DEET or possibly one of the other ingredients common in insect repellent. So when I’m going to be outside I hang my clothes up and spray them before dressing. Works pretty effectively.

    3. While I’m happy that this neurotoxin stuff was just blown out of proportion, I’m a little concerned about your other advice. I work at a vineyard so we regularly (and I mean two or three times a day) dose ourselves down with bug spray, the name of which I can’t remember but I read on the can has 23.3% Deet. It’s hot out there so we’re usually in shorts and tank tops meaning the spray goes right on our skin, not our clothes, otherwise the bugs would (and have when I forgot the spray) eat our arms and legs. Also, we almost always have sunscreen on in combination with the spray because once again it is HOT out there and we’re in the middle of a huge field, we need the sunscreen.
      I was told that this spray was the only one they found effective, given our work conditions, but after reading this I think I might look for an alternative.

    4. DEET is the best one for your work conditions.
      The other stuff available in the US will not work for you if you have lots of mosquitoes and other biters.

      Putting it on skin is fine; just *under* clothing is not recommended. And hopefully you take a shower at the end of the day, so that is not an issue :)

      20%/23%–not a big difference. Mostly I just want people to not purchase the crazy amounts that are available in stores. You don’t need 50% or 100% DEET unless you….well, honestly, I can’t think of a situation in which you would need it.

    5. Laura Jefferson August 10, 2009 at 8:26 am

      I was the only one on my dig (wet northern NH — mosquitoes, black flies, hideous no-see-ums) not using DEET and I had good results with Badger Bug Balm. It does need to be applied more often, but when people couldn’t cope but we still cautious enough not to put DEET on their faces they got relief using the Bug Balm.

    6. I thought this might be an interesting addition to the topic:
      Media Health reporting could be dangerous to your health

      also–bug balm? Ugh!
      Sounds pretty messy. is it?

    7. Hello, thanks for the link!

      Do you think there’s any benefit to having more than 20% DEET? When I went to Vietnam & Thailand I used 100%, and the weakest they were selling in the shop I bought it (in the UK) was 50%.

    8. That’s disturbing. There is no benefit to the higher doses (>25%) in field studies, so I wouldn’t use it. You’re basically paying for extra DEET that doesn’t have any added protection.

      Of course, I have insanely sensitive skin, and react to anything. 20% DEET is all I can tolerate. I can’t wear most sunscreens either, so I tend to just wear protective clothing a lot and sweat like crazy. :(

    9. The manufacturers claimed that the benefit of the stronger stuff was that you had to apply it less often.

      Personally, I just found the stronger stuff melted plastic faster…

    10. Thanks Bug Girl, it’s good to know I wont die tomorrow or anything.

    11. Depending on which reports you read, recently, the CDC has proclaimed Picaridan to be as effective as DEET. For the last 2 years, I have been using Cutter Advanced on my skin for mosquitoes, ticks and chiggers. Extremely effective. For heavily infested chigger areas, I spray my socks, shoes and pants legs. 2 years ago when Martha and I were on the Alaskan tundra with hordes of mosquitoes, we used Picaridan on the skin and DEET on the clothing. This worked like a miracle.

      The nice thing about Cutter Advanced is that it is nearly odor free and won’t stain clothing or leather.

      For a link to cutter information, Click here.

      I like your blog a lot. Bookmarked it.


    12. I just noticed yesterday that REI now has a 20% Picaridan solution. I’ll check it out

    13. awesome post. I am linking to this.

    14. Troy– That’s good, and a new development–the initial formulations of Picaridin were not high enough to do much in comparison to DEET.

      Initially, only 10% was available in the US.

    15. […] when I’m up in Tahoe, exploring high altitude bogs in the Desolation Wilderness. And also BUG GIRL says that maybe these studies aren’t that useful anyway: “The results in this paper are […]

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