About a year and a half ago I began researching the most troublesome bugs and the effectiveness of the available repellents. The purpose of this was to make a more informed decision as to which repellents worked best and more importantly, to understand the limitations and potential risks of each repellent. I learned a lot more than I thought I would. Most of the Web based data comes from manufacturer, government, medical, and university web sites. I also did some on the trail research. I thought this would be a "DEET vs. the World" contest. It appears however, DEET's nemesis is itself.

***************************************************

NOTE 1:
What works for one person may not work for another, and what works on one specific insect may not work on a similar species. For example; if two people apply the same repellent to themselves, one person may not get bitten once over the next 8 hours and the other person may get eaten alive after just a couple of hours, and DEET and Picaridin are each highly effective against certain species, but not necessarily the same species. The repellent you apply at the trailhead may be nearly 100% effective against the skeeters there, but two miles up the trail you may encounter a different species of skeeter who isn't bothered much at all by that repellent. In other words, "Your Mileage May Vary".

NOTE 2:
For those of you out there who are highly resistant to change please go back and read NOTE 1 again before you post how you've used "abc" repellent for 60 years and it's always worked and you tried "def" repellent once and it didn't work at all.

**************************************************

The bugs studied were: Mosquitoes (Carriers of Eastern Equine Encephalitis {EEE} and West Nile Virus{WNV}), Black Flies (Most persistent pests), and Deer/Blacklegged Ticks (Carriers of Lyme Disease). There are other biting insects around, but these three are the ones that many of us are most concerned with. I have a brief comment on another biting insect, the Deer Fly.

The repellents studied include: DEET, Picaridin, and Oil of Lemon Eucalyptus, which are the three recommended by the CDC. There are a few other repellents out there including Citronella Oil, Peppermint Oil, and Cedar Oil, but their effectiveness is very limited and in some cases they're as toxic as the chemical repellents they replace.

Bugs:

Mosquitoes
There are 47+ species of mosquitoes in New England, but only the females of a few species can transmit EEE or WNV from birds to mammals. It’s important to note that insect repellents are not equally effective against all species of mosquitoes.

WNV is more likely to be transmitted to humans and their pets than EEE; However, WNV usually causes only mild symptoms in people, less than 1% develop serious symptoms. Dogs and cats are unlikely to display any noticeable systems from WNV if infected.

EEE may be less common than WNV, but it is far deadlier. The mortality rate in humans is about 35%, higher in non-native species such as dogs, cats, horses, llamas, etc., and lower in native species such as: white-tailed deer, moose, and other native animals which have had thousands of years to build up a natural resistance to it.

Black Flies
Like mosquitoes there are 40+ species of black flies in New England, fortunately only the females of a few species bite, perhaps more troublesome than the biters though are the Simulium jenningsi. These are the notorious late season swarmers. As pesky as black flies are I found no information linking them to viruses or other health risks. Repellents that are effective against mosquitoes are generally effective against black flies as well, but usually to a lesser degree.

Deer Ticks (also known as blacklegged ticks)
These tiny villains are the carriers of the dreaded Lyme disease. As far as I know, Lyme disease is not fatal, but it can create a serious disability if left untreated. 

T. J. Dunn, Jr. DVM on Lyme disease in dogs:
“Of the hundreds of cases of canine Lyme Disease that I have seen, over 90 percent of canine patients were admitted with signs of limping (usually one foreleg), lymph node swelling in the affected limb, and a temperature of 103 degrees (101 to 102.5 degrees is normal). The limping usually progresses over three to four days from mild and barely noticeable to complete disuse of the painful leg…”

Deer Flies
Deer flies are the worst. DEET doesn't faze them, their bite is painful like maybe 50% of a bee sting, they're much faster than black flies and mosquitoes; and they know how to draft (I've gotten a back full of deer fly bites while road biking). Mosquitoes, black flies and deer ticks can be effectively dealt with using bug spray, long sleeves/pants, head nets, cigars and many other means. However there is not an effective way to deal with the dreaded deer fly. In my experience, DEET and other insect repellents doesn't affect them. Trying to kill them has a low success rate, at least for me. Wearing a hat works for a while, until they decide that hitching a ride on it will not get them fed. That's when they dive down on your back and bite you through the shirt or start making loud, high speed circling runs before landing on the back of your neck. The absolute worst is when you have three or four dive bombing you at the same time. In that case, the noise and the sight is clearly more annoying than the bite.

Insect Repellents

Lemon Eucalyptus and other Essential Oils
Many people use essential oils instead of their chemical cousins because they believe that all natural compounds are safer. Consider this: poison ivy, hemlock, strychnine, and cyanide are also "all natural". Just because something is not considered a chemical, don't assume it's safe to use. Many of the essential oils used to repel insects are toxic to some degree and most are highly toxic to cats. For example, lemon eucalyptus oil can cause permanent blindness if it gets in your eyes and peppermint oil is a carcinogen and citronella oil is to bears what catnip is to cats and bears have the best noses in the woods. While the chemical repellents have decades of research and testing which support their safety claims, Essential Oil repellents are not scrutinized nearly as much and some of their claims may be completely unsupported. Combine this with the fact that essential oil repellents are only marginally effective against mosquitoes and black flies, almost useless against ticks, and the effects are only good for about 30-60 minutes. Why not just use something that works.

Picaridin
Picaridin, aka Icaridin, KBR 3023, Bayrepel, IR3535, and KBR was developed by Bayer AG of Germany in the 1980's. Bayer used 3D computer modeling to create a repellent at the molecular level that could block the sensory receptors of malaria carrying mosquitoes of the Anopheles genus as well the Blacklegged tick (Deer tick). The result was a repellent more effective than DEET against the aggressive Asian and African species of mosquitoes as well as stable flies and deer ticks; and as effective, or nearly so, against most other mosquitoes, flies, and ticks.....and Picaridin does this without the adverse side effects of DEET. In numerous laboratory tests, the most serious effects on test animals were to rats that were fed 5,000mg./day of Picaridin. They suffered liver damage. For you or I to get the same equivalent dosage we'd have to drink 15-20 cans of Picaridin a day....Compare that to the fact that as little as 2-4 ounces of DEET will kill a person. Picaridin is practically non-toxic to most mammals including humans, dogs, and cats; and it doesn't dissolve plastics and other synthetics the way DEET does. It's also biodegradable, making it much safer for the environment. Picaridin however, doesn't work the same way DEET does. It forms a defensive barrier on the skin which can take 15-30 minutes to form. Until then it's very ineffective. So give it time.

DEET
N,N-diethyl-meta-toluamide (DEET) was invented by the U.S. Department of Agriculture in the mid 1940's for use by the Army and it was made available to the public in 1957. For 50 years DEET has been the most effective longest-lasting mosquito and black fly repellant available. Despite it's super-effectiveness DEET has a few drawbacks.

1) DEET dissolves many plastics and other synthetics including: backpacks, clothing, watch crystals, cameras, paint finishes, sealants, as well as many other products.

2) The stuff repels humans almost as well as it repels insects due to it's smell and the greasy feel it leaves on the skin.

3) DEET applied to the skin is absorbed by the body. It is then excreted through perspiration and urination. That's right, you'll pee DEET for up to 24 hours after using it. After you flush and wash off the DEET applied to your clothing and skin it is sent off to a water/sewer treatment plant where the DEET will pass right through because these facilities were not designed to break down DEET and DEET is not biodegradable. For over 50 years DEET has been accumulating in our rivers, lakes and oceans, and recently it has been discovered that even some of our nations municipal water supplies have measurable concentrations of DEET in them. So what risk is there to the environment?

From the 1998 E.P.A. R.E.D. fact sheet:
"...Because DEET is only applied directly to the human body/clothing, cats, dogs, pet quarters and household/domestic dwellings, it is considered to be an “indoor residential” use...Ecological risk assessments are not conducted for pesticides with exclusively indoor use patterns. Application of DEET to the human body/clothing, cats, dogs, pet quarters, and household/domestic dwellings, is not likely to adversely affect terrestrial wildlife or aquatic organisms..." Obviously written by a politician!

4) Finally, it has been demonstrated (proven) that DEET can react with other chemicals/drugs in the body to produce unexpected and even fatal consequences, especially with DEET concentrations greater than 30%. A Canadian medical bulletin stated that DEET may have significantly greater toxicity when combined with ethyl and/or isopropyl alcohols and freon which are common in some DEET products. It has also been shown in laboratory tests that extended use of DEET kills neurons in the brain that control muscle movement, learning, memory and concentration. It shouldn't be any surprise that many countries, as well as New York City, have banned repellents with high concentrations of DEET or have banned DEET altogether. Note: The combination of DEET and an experimental drug (PB) used by Gulf War veterans is suspected by some researchers to be the cause of Gulf War Syndrome.

Permethrin
Insect repellents are generally less effective against deer ticks than they are against mosquitoes and black flies and the effects last for a much shorter duration. Another option is Permethrin, an insecticide with repellent properties which is considered safe for humans, dogs, and horses, but it's highly toxic to cats. It can be sprayed on your clothing and it kills ticks on contact and will last through several wash cycles. Ticks generally don't get more than 6-12 inches across a treated fabric, and if they're only on the fabric for a few inches they'll likely die before they can transmit Lyme disease to you, which usually takes at least 24 hours. Permithrin is generally safe to spray on skin, however due to the type of solvents used it will not bond with your skin and evaporates rapidly. Sprayed on your skin it's benefits are only good for about 15-20 minutes. Permithrin treated clothing in conjunction with DEET or Picaridin on your skin will make you virtually immune to Mosquitoes, Black Flies, and Ticks. While permethrin is highly effective on the trail, where it really excels is around the house. I use it in the entryway to combat the bugs that get in when my neighbor leaves the front door propped open at night and it's just Awesome when used strategically against sugar ants.

Both DEET and Picaridin were tested against grass, dandelions, and household plants. Both performed flawlessly. They are effective defoliants.

The information I've posted above is, to the best of my knowledge, accurate and seems to represent the general consensus among industry professionals and researchers from various organizations including; The C.D.C., W.H.O., manufacturers, various universities, reviews and tests performed by foreign governments and military's, as well as other sources.

Insect Repellent Brands

5) There is also 3M Ultrathon, it is Deet based and was developed for the US military. The Deet concentration is around 30%. What makes it different is that it is mixed with a compound that keeps it from soaking in the skin. The best description I could give is that is similiar to skin barrier cream used for working with chemicals that could affect the skin. I find that Ultrathon lasts substantially longer than regular Deet, and it doesnt tend to dissolve plastics like 100% Deet. I wouldn't recommend it for short term exposure situations, rather its good for all day exposure to bugs. The down side is that at the end of the day, its more difficult to wash off.

6) As for deer flies, many techniques have been tried and not worked perfectly, including Deer Fly Patches and the fern in the cap trick. The best thing I have found is wearing a hat sprayed with Skin So Soft. They seem to hit my head once or twice and then fly off. Unfortunately, they occasionally decide to drop down to my neck or back and chomp me, but thankfully not often.