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Last week I was hiking in Washington state and the mosquito situation was extremely bad, so I had to spray DEET all over my hands which I don’t do normally. This got me thinking - just how poisonous is this substance if accidentally ingested? I.e. if I forgot about the bug spray and ate a sandwich without washing my hands, would I have had food poisoning as a result?

I was able to find a report of serious adverse effects from ingesting 80 mg/kg of DEET which works out to about 6 grams at my body weight. But what is the lowest dose that could be accidentally ingested without immediately panicking and going to the ER?

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  • You found that one report of, but did you look any further? I can’t write an answer right now, but take a look at the links here for more comprehensive information, rather than a specific case study, and you should also note that the paper you linked also specifies the dangers to children rather than adults. Jul 8 at 0:29
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    Just as an aside, this would not be "food poisoning" (the food itself wasn't bad), it would still be "DEET poisoning". Jul 8 at 0:48
  • I've modified the title to better match the body, because as it stood the question looked unanswerable without knowing what the repellant was made of - but we do know. It would be worth looking at the other ingredients too, but those of the 50% DEET I have (Jungle Formula) aren't concerning
    – Chris H
    Jul 8 at 10:27
  • Tip for next time - use the backs of your hands to spread it; avoid getting on palms or fingertips especially of you dominant hand. It tastes bad and can damage some plastics, synthetic fabrics and other things you might handle
    – Chris H
    Jul 8 at 10:29
  • @ChrisH did you mean to change the title to DEET rather than DDET? Jul 8 at 10:33
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First off - with anything health related, if you feel effects that are atypical and are concerned, get to a doctor. The advice we can provide here should in no way be considered medical advice or substitute for proper medical procedure.

It is impossible to say what the lowest dose is for any one individual - it depends on your personal sensitivity to it, how long an exposure (1 time, many times, over how long? (minutes, hours, days, weeks?)), exposure route (oral? inhalation?), age, gender, etc. Obviously incidental exposure when you are applying it will happen, but you aren't likely to panic and rush off to the hospital for that, but how much beyond that is impossible to say.

Values in the literature are usually expressed in terms of LD50 (lethal dose for 50% of population studied), but this is in a model animal (rat or mouse usually) and will be well above the dose at which you could get sick.

Having said that the CDC has a fairly comprehensive report (PDF) on the literature, with some human cases of all sorts of routes of exposure.

Based on the OP's comment to this post:

The OP is talking about an acute oral exposure. The lowest value with what is known as NOAEL (No Observed Adverse Effect Level) is 100 mg/kg/day for rats, dogs and rabbits in the CDC document linked above (see table 3-2, pp. 33-43). If you extrapolate that value to a human of 50 kg that is 5000 mg or 5 g per day. This equates to very close to 5 ml (1 teaspoon) of 100% DEET per day (density of DEET = 0.998 g/ml).

This NOAEL is for a variety of physiological systems: systemic, developmental, hepatic, reproductive and immunologic. Values for other systems were at least double the 100 mg/kg/day value discussed above.

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    In the question, the OP does give the oral route as a one-time exposure (ingestion from not washing hands before eating). This answer would be improved by specifying some numbers from the linked report. Jul 8 at 1:38
  • @fyrepenguin - that's still not necessarily a single dose at one time, could be anything from repeated doses over several days or weeks in the context of the outdoors. It could also be minor repeated doses over say an hour (that's pretty long to eat a sandwich) leading to a cumulative dose. No mention of prior exposure or how the DEET was applied or concentration in the product applied. I agree about quoting information, but until OP clarifies their question this is all moot. The first part of my answer is the important bit... it's a "how long is a piece of string question?"
    – bob1
    Jul 8 at 2:50
  • To give an example, if my hands were covered in arsenic and I then proceeded to eat a sandwich, I’d probably rush to the closest hospital to be safe. With DEET I have no idea if I should just ignore such an exposure or worry about it. Jul 8 at 4:03
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    @bob1 true, but DEET also appears to be notably less toxic through inhalation than through the oral route, oddly enough. Not that it changes the answer, but it's important to compare apples to apples. Jul 8 at 4:59
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    @fyrepenguin interesting, though I note that the value there is 5.95 mg/l, how that equates to mg/kg, I have no idea, but the mg/kg value is in the 100s of mg/kg, suggesting that uptake from the lungs is greater and of more risk. I note the CDC paper I linked shows NOAEL values of 1511 mg/m^3 (1000 litres = m^3), but that was the highest conc tested, so hard to say.
    – bob1
    Jul 8 at 8:38
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While there seems to be some personal variation, with children more sensitive than adults, it's not particularly likely for incidental exposure via your lunch to cause you an issue.

The particular report you were looking at was a single case, for a child, who seem to be more sensitive than adults, who was exposed to 80 mg/kg. While that's concerning, particularly regarding keeping children from ingesting it, it also doesn't constitute a large study, and as children are known to be more sensitive, I wouldn't use it as a cause for alarm in your own situation.

You seem to be more concerned with acute exposure via oral ingestion, which (in rats) is on the order of 500-5,000 mg/kg. There are specific cases in humans (page 31) of acute toxicity, where adults ingested significantly more than the case you've cited for your concerns. There two cases where adults (one man, one woman) ingested 50 mL of 95% DEET, one where a man ingested 235 mL of 11%-50% DEET, and one where a man ingested about 180 mL of 40% DEET. All of those cases are very difficult to do unintentionally, or as part of incidental exposure through application to yourself and your food.

DEET can have adverse effects due to chronic exposure, or via very extensive dermal exposure, but I would not be concerned about more limited exposures, even orally. Just don't try to use it as a breath spray, is all.

Some interesting reading on the chronic toxicity can be found in the EPA report and this other paper.

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Given the taste, I am not very worried about getting a 1 teaspoon dose (~5g) Even handing food with hands that had DEET applied some time before results in food tasting awful.

In the FWIW department, I did a several week canoe trip each year for decades, and would bring a 3.5 oz bottle of 95% DEET. Over the course of the trip I'd use about half of it, mostly on hands and hair and back of my neck.

A trick to reduce your exposure is to apply it to the rim of your hat, your collar, shirt and pants cuffs.

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  • And Permethrin is an option to treat clothes semi-permanently (though beware of its toxicity to cats) Jul 15 at 10:05
  • Is permethrin an effective repellent? Jul 16 at 12:56
  • AFAIK it’s fairly effective, though can only be used on clothes. “Permethrin affects the neurological system of insects. Upon contact with permethrin-treated surfaces, mosquitos, ticks, chiggers and other insects will fall off almost immediately, nearly all will die from this brief contact”. It’s a neurotoxin, also used for treating scabies, lice, and fleas (for dogs). Generally fairly safe for dogs and humans, though highly dangerous (when wet) to cats. The main advantage is treating clothes and being able to wash them a few times before it loses effectiveness Jul 16 at 16:23

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