With the recent rains, many people are concerned about mosquito bites and the possibility of contracting the West Nile Virus. One way to reduce the likelihood of getting bitten is to use an insect repellent when spending time outdoors in mosquito-infested areas. The following information may help you decide about what repellents will be effective.

DEET. Right now, the most effective insect repellent on the market is still DEET, diethyltoluamide, a chemical developed in the 40's for the U.S. Army. Products containing DEET have been available to the general public since 1957. DEET has broad spectrum activity and is effective against mosquitoes, biting flies, midges, chigger, fleas and ticks.

DEET repellents come under many brand labels (such as SkinTastic, Cutters, Deepwoods Off, Skin So Safe, Skeedaddle, Repel, Muskol, etc.), and many formulations (lotions, gels, aerosols, creams, sticks, wipes) of varying strengths, ranging from 5 - 95 percent.

Depending on the situation, DEET provides 2-8 hours of protection. One application of DEET at 50 percent strength protects from mosquitoes for more than 4 hours while a similar application of a 100 percent formulation may last for 12 - 14 hours or, if applied directly to clothing, for as much as 10 days. High temperatures and humidity reduce the length of effectiveness. In such a situation, it may be necessary to apply the repellent more often or use a slightly stronger concentration.

HOW DOES DEET WORK? The material apparently works by interfering with mosquitoes ability to detect convection currents caused by a warm body after they have been alerted by their carbon dioxide receptors. Hairs on the antennae are temperature and moisture sensitive. Mosquitoes apparently do not avoid people because of the odor of DEET, rather it is thought that DEET molecules somehow interfere with the entry pores of the female mosquitoes sensory receptors, thereby interfering with their ability to locate their hosts.

THE HAZARDS OF DEET AND HOW TO AVOID THEM: Several years ago, the Environmental Protection Agency issued some precautions regarding the use of DEET repellents, due to some reported adverse effects on young children. In a consumer bulletin entitled, "Using Insect Repellents Safely," the agency stated, "While doctors have not confirmed DEET as the cause of reactions such as headache, mood changes (crying, irritability), confusion, nausea and, in severe cases, muscle spasms, convulsions or unconsciousness, EPA is concerned that a small segment of the population may be sensitive to DEET." They indicated that overuses of DEET repellents may have resulted due to public concern over tick-related diseases, such as Lyme Disease. Also, many of the adverse reactions reported appeared to have involved accidental exposure, such as swallowing or spraying into the eye. The agency has issued the following precautions regarding the use of DEET repellents:

1. Apply lightly, only to exposed skin and clothes, not under clothing.
2. Do not apply over cuts, wounds or irritated skin.
3. Do not get into eyes or mouth.
4. Do not apply to hands of young children.
5. Do not reapply or saturate skin.
6. Wash treated skin between uses.

People who work outdoors and use DEET regularly should be aware of the possibility of reaction if DEET products are overused. Remember to treat clothing rather than skin, but be aware that DEET can damage plastics, leather, and synthetic fabrics like rayon.

Apply the products lightly, particularly if they are concentrated materials. For casual use, a product containing 10-30 percent DEET should be adequate. For children, it is best to be conservative and keep the concentration of DEET at 10 percent or less. Be especially careful with small children, anyone who has a history of sensitivity to chemicals and the elderly as these groups are more likely to have a reaction.

The Agency estimated that 50 - 100 million people use DEET repellents each year, with 10 or fewer reported cases of neurological intoxication as a result of applications to skin. EPA did not suggest that people stop using DEET due to its overall benefits of insect and tick repellency. Make sure to use products that were made after 1993, because some earlier products contain an adhesive that has raised some concern.

You must balance the risk against those of irritation, secondary infection of bites and the possibility of transmission of insect-borne diseases.

For more on this subject, we suggest that you go to the EPA website and review two articles, one entitled The Insect Repellent DEET and the other How to Use Insect Repellents Safely. They can be accessed on the web at http://www.epa.gov/oppts/opptsconhome.htm

Citronella. Derived from a lemon-scented grass and found in oils, sprays and candles, citronella is a common ingredient in many repellents. Studies have shown that citronella oil protects against most mosquito bites during the first 30-40 minutes after application, but is effectiveness diminishes quickly and is gone in two hours.

IR3535. This repellent (3-[N-butyl-N-acetyl]-aminopropionic acid) is the most recently marketed chemical repellent in the U.S. It is available exclusively through the Avon Corporation as Skin-So-Soft Bug Guard Plus IR3535. It is labeled for use against mosquitoes, ticks and biting flies. In some studies IR3535 provided protection for 4-6 hours, but another study performed at USDA laboratories found that 25% IR3535 was 10-100 times less effective than DEET.

Skin-So-Soft bath oil. Made by Avon, this oil has been shown in laboratory tests to have a minimal repellent effect. By comparison, 12.5 percent DEET provided protection from bites for 10 times longer.

Soybean Oil, Geranium oil and Coconut oil. These oils have been formulated into a product called Blocker which has been available in the U.S. since 1997 This “natural” repellent worked much better than citronella-based repellents. In some studies, Blocker provided complete protection against mosquito bites for as long as 3.5 hours.

Future Repellents

Piperdine. The USDA Agricultural Research Service is looking at this molecule which has repellent properties and is found in trace amounts in black pepper. Advantage to piperdine-based repellents is that they won’t dissolve plastics, such as sunglass lenses or auto paint.

Catnip. Researchers at Iowa State University have found that nepetalactone, an essential aromatic oil in catnip, is about ten times more effective at repelling mosquitoes than DEET — the compound used in most commercial insect repellents. A patent application for the use of catnip compounds as insect repellents was submitted last year by the Iowa State University Research Foundation. Don’t expect this to be commercially available anytime soon, as it has yet to be analyzed by the US-EPA or tested by human subjects.

Tomato. A North Carolina State University entomology researcher has reported that a component of tomatoes, called IBI-246, has shown itself to be more effective that DEET and is safer. It repels mosquitoes, ticks, biting flies and even cockroaches. A company called Insect Biotechnology has purchased an exclusive license from NCSU to develop the product. It has been tested on humans with no adverse side effects, but it still has to be approved by the EPA before it can be marketed. Updated 9/10/02

Return to Insects, Spiders, Mice & More...