Overblown DEET news

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.