Insects have evolved to recognize certain sensory stimuli-say, the scent of human perspiration, or the carbon dioxide we exhale or that seeps from our skin-as an indication that there is a food source nearby for them. When those signals are altered to be unrecognizable or to confuse the sensory apparatus of insects, they have no way of knowing just how close they are to a delicious meal of blood. So it’s like putting blindfolds on them.
This is the biological basis for most insect repellants. Insect repellants typically aren’t insecticides that actually kill insects, nor do they usually literally “repel” insects in the sense of driving them away. What they do is mask the scents, the signals, that attract insects to us.
There are several insect repellants that have proven to be quite effective.
For application to the skin, there are products containing N,N’-diethyl-3-methylbenzamide (DEET), long the gold standard of insect repellants. Developed by the United States Army, DEET has been used by the military since 1946, and by civilians since 1957. It is a yellowish oil that is present in varying concentrations in insect repellants, from 5% to 100%.
More recently, a serious contender to DEET has arrived on the scene, in the form of the chemical hydroxyethyl isobutyl piperidine carboxylate (icaridin, or picaridin, or picaradine). Icaridin, developed by the Bayer company, has tested out to be of comparable effectiveness to DEET as an insect repellant. Plus, while DEET can cause skin irritation in some people, and can dissolve plastics and damage synthetic fabrics, icaridin does not seem to cause these problems.
For application to clothing, the chemical permethrin is the best insect repellant. Clothing can be purchased that has been pretreated with permethrin, or it can be sprayed onto or soaked into the fabric by the consumer. Permethrin, it should be noted, is not safe for use directly on the skin.
If you’re using any kind of chemical repellant like these, be sure to always follow the directions meticulously.
In addition to these repellants, there are many popular natural insect repellants. However, these alternatives have typically not been tested to the extent the above have. Where they have been tested, they have not fared nearly as well as products with DEET or icaridin. Expert opinion ranges from (1) they can be somewhat effective for shorter periods of time than DEET or icaridin, to (2) they basically have no beneficial effect beyond the psychological one of enabling the user to feel good about using natural or green products.
But for those who do prefer to go the natural route, among the substances people most often report using with success as insect repellants are:
* Citronella oil
* Lemon eucalyptus oil
* Lemongrass oil
* Peppermint oil
Using an effective insect repellant is not just a matter of comfort or convenience. Mosquitoes and other insects carry serious, sometimes fatal, diseases. So having the right protection can literally be a matter of life and death.
Jack DeAngelis, “Mosquito/Insect Repellents.” Living With Bugs
“Tick and Insect Repellents: Deciding on Their Use.” New York State Department of Health