Insect Repellents
By Wm. A. Sodeman, Jr., M.D., J.D.,
(June 2003 FFF Clubwire)
In July of 2002 the New England Journal of Medicine published an article written by Mark S. Fradin, M.D. and John F. Day, PhD on the effectiveness of various insect repellents. These authors used mosquitoes in their testing. Diseases caused by biting insects, particularly mosquitoes, are responsible for a great deal of death and disability worldwide and that is the reason for a scientific study of the effectiveness of insect repellents on mosquitoes.
The information provides a collateral benefit for those of us bothered by mosquitoes while fishing. Herewith is a brief summary of the information they obtained. Anyone who wishes to look at the original paper can find it in the July 4, 2002 issue of The New England Journal of Medicine, Volume 347, p. 13.
Insect repellents were tested by applying the repellent to the arm of a volunteer and then having the volunteer stick his or her arm into a cage full of mosquitoes. The time to the first bite was recorded. If there was no mosquito bite after the first minute then the volunteer removed his or her arm from the cage. The treated arm was reinserted at regular intervals until a bite eventually occurred. A great deal of care was used to insure that test was free of bias and error.
The good news is that products containing 20 percent DEET offered protection from mosquito bites for an average of 4-5 hours. For most of us this means bug free fishing with a need to reapply repellent only once, or at the most twice if you are going to make it a long day. The bad news is the lesser concentrations of DEET, below 20 percent, offered protection only in the one and one half hour range, which would mean more frequent interruptions to reapply.
I had been concerned in the past about rumors of possible toxic side effects from DEET and was heartened to find that it has an excellent safety profile. It has been used for 40 years and there have been approximately 8 billion human applications. Out of this 8 billion there have been fewer than 50 cases where there have been serious side effects and only 13 produced any kind of residual effect. This works out to one bad residual event for every seven and one half million applications. My guess is it would probably be safer to use DEET than it is to wade the stream.
For those few people who are allergic or sensitive to DEET there are a couple of alternative options that seem to work. They are effective but not as long lasting.
- There is a soybean oil based preparation (Bite Blocker for Kids) that gives about an hour and a half of protection.
- Eucalyptus oil preparation (Repel Lemon Eucalyptus Insect Repellent or Fite Byte Plant-Based Insect Repellent) that on average works for two hours.
- The rest of the repellents tested seem for all practical purposes to be useless. Herbal preparations containing citronella were effective for 10 to 20 minutes, IR3535 for 22 minutes and the skin softening preparations, which have had a great deal of popularity, seem to be even less effective at 10 minutes or less protection. If you use these you will spend more time applying insect repellent than fishing!
- The wristband preparations and presumably the stick on tabs, though they were not tested, including those impregnated with DEET, did not give a full minute of protection.
- Other studies have shown that the small mechanical devices that emit sounds that are supposed to scare away mosquitoes are ineffective.
Based on these studies, the strategy which I will adopt is to use Deep Woods OFF which contains 23.8 percent DEET or Sawyer controlled release which contains 20 percent DEET. (I pick these because they were the ones tested, but there is no good reason why any DEET preparation of 20 percent or greater would not work as well.
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