How long does DEET last?

[Mr. Jowee]

I mean when worn on your person, not shelf life. I generally don't put any on until I start to notice mosquitos, but last weekend I was attacked by/infested with chiggers. Unlike mosquitos, chiggers are out during the day while hiking, and you won't even know they are attacking until the following morning. Re-apply every 4 hours? 5 hours?

[MuddyWaters]

I've had my share of run ins with chiggers, never in the mountains though. Always high grass and weeds in lowlands. Long pants and permethrin treated pants, shoes, socks works. The came thru mesh trail runners and bit all over my feet once when shoes were untreated. Never a problem after treating. Stay out of high weeds and grass wearing shorts.

[winger]

Good question, and I don't have an exact answer, but some of the duration would be affected by perspiration and possibly ambient temperature. I tend to reapply every 4-6 hours. There is probably an in house chemist who can provide a more accurate estimate.

[GoldenBear]

http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/protection-against-mosquitoes-ticks-and-other-insects-and-arthropods


Published data indicate that repellent efficacy and duration of protection vary considerably among products and among mosquito species. Product efficacy and duration of protection are also markedly affected by ambient temperature, level of activity, amount of perspiration, exposure to water, abrasive removal, and other factors. In general, higher concentrations of active ingredient provide longer duration of protection, regardless of the active ingredient. Products with <10% active ingredient may offer only limited protection, often 1–2 hours. Products that offer sustained-release or controlled-release (microencapsulated) formulations, even with lower active ingredient concentrations, may provide longer protection times. Studies suggest that concentrations of DEET above approximately 50% do not offer a marked increase in protection time against mosquitoes; DEET efficacy tends to plateau at a concentration of approximately 50%. CDC recommends using products with ≥20% DEET on exposed skin to reduce biting by ticks that may spread disease.

As a minor aside, for years I just accepted that I would get one to two mosquito bites a day while hiking on the A.T.
This year I started wearing knee-high, wool socks -- and, more often than not, I have gone a week without one bite. Don't know if it's because I spray on DEET more religiously, I've been hiking in drier areas, or if the knee-highs have saved my legs. All I know is that I'm not getting bit as much.

[Mr. Jowee]

That's some really good info, though my main concern are chiggers rather than mosquitos. If I'm getting bit by mosquitos, I'll know it and can apply more repellent as needed. With chiggers you just don't know. I never even thought to treat my shoes with permethrin (though all of my clothes are).

[Leanthree]

The higher % DEET the less frequently you need to apply.

My rule of thumb with 99% DEET is if I am sweating a lot then every 2-3 hours. If not much sweat then it can last about 8 hours. YMMV.

[Rocket Jones]

I've heard that DEET above about 40% doesn't offer greater protection. My experience seems to confirm that.

[daddytwosticks]

I'm usually bothered severely by chiggers. The last two years, they haven't seemed too bad in these parts. Several years ago, while hiking from Stecoah Gap to the NOC, I was positively eaten up by chiggers. I think it was from my prolong break in the tall grass atop Cheoah Bald. :)

[peakbagger]

The government worked with 3M to develop Ultrathon for the military, which is a lower percentage Deet compound that lasts 8 to 12 hours. The Deet is mixed with a product that keeps it on top of the skin instead of being absorbed. I have used it for several years and it definitely seems to be good for 8 plus hours.