DEET Still Tops at Beating Mosquitoes

July is typically the month in which biting insects like mosquitoes become a problem for those of us who enjoy spending time outdoors. Once mosquitoes begin to hatch and breed, events such as lakefront festivals, outdoor picnics and church fairs can become a mosquito free-for-all at the expense of you and your exposed flesh.

In addition to the annoying itch that comes with mosquito bites, these days we also wonder if we should start worrying about mosquito-borne diseases like West Nile Virus. Arriving in North America in the summer of 1999, West Nile Virus has claimed the lives of 18 people on the East Coast, and the Centers for Disease Control and Prevention (CDC) estimates that up to 2,000 people were infected in the year 2000. It has since been detected in dead birds in many states.

So what do you do about those pesky mosquitoes? Browsing the aisles of your grocery or drugstore, you can find a confusing array of products designed to keep bugs away from you and your family, but how can you tell what works and what doesn’t? Which one lasts the longest? Which is safe for children? And are the so-called “natural” products any better for you than synthetic ones?

According to Gary Barnas, MD, Associate Professor of Medicine at the Medical College of Wisconsin, once you know your products the choice is fairly simple. “You should be looking for the best insect repellant for the money," he says, "the one with the longest duration.”

The New England Journal of Medicine (Vol. 347, No. 1, July 4, 2002) has published the results of a laboratory study conducted on insect repellants. The results, while not surprising, give consumers a definitive answer as to the effectiveness of the various products available. The study showed that products containing N,N-diethyl-3-methyl-benzamide – known to most of us as DEET – were most effective in repelling insects for long periods of time

Concerns about the safety of DEET have been widespread in recent years, but documented side effects from DEET have occurred infrequently, and only developed after extreme overuse. Users should always apply only the amount specified on the product’s package. Says Dr. Barnas, “There won’t be any side effects if the product is used prudently.” Infectious disease specialists also point out the fact that the advantages of insect repellants, especially in areas where mosquitoes may spread dangerous illnesses, far outweigh the disadvantages.

It is important to note that this study was conducted in a laboratory and not in the outdoors. This means that a product that failed in the lab would certainly be a failure in the field. But a product that did well under ideal lab conditions may or may not fare as well in the field, where different kinds of mosquitoes could be present, and conditions such as environment and climate can alter results. Also, the amount of DEET in the products tested varied. On the low end was OFF! Skintastic for Kids, which contains 4.75% DEET. On the high end was OFF! Deep Woods, with 23.8% DEET. Coincidentally, both products are made by SC Johnson right here in Wisconsin.

The list below shows the products tested, along with their active ingredients and the average amount of time that each product repelled mosquitoes.

1. OFF! Deep Woods (DEET 23.8%) - 301.5 min.
2. Sawyer Controlled Release (DEET 20%) - 234.4 min.
3. OFF! Skintastic (DEET 6.65%) - 112.4 min.
4. Bite Blocker for Kids (Soybean Oil 2%) - 94.6 min.
5. OFF! Skintastic for Kids (DEET 4.75%) - 88.4 min.
6. Skin-So-Soft Bug Guard Plus (IR3535 7.5%) - 22.9 min.<
7. Natrapel (Citronella 10%) - 19.7 min.
8. Herbal Armor (Citronella 12%; peppermint oil 2.5%; other ingredients <2%) - 18.9 min.
9. Green Ban for People (Citronella 10%; peppermint oil 2%) - 14.0 min.
10. Buzz Away (Citronella 5%) - 13.5 min.
11. Skin-So-Soft Bath Oil (Uncertain) - 9.6 min.
12. Skin-So-Soft Moisturizing Suncare (Citronella 0.05%) - 2.8 min.
13. Gone Original Wristband (DEET 9.5%) - 0.3 min.
14. Repello Wristband (DEET 9.5%) - 0.2 min.
15. Gone Plus Repelling Wristband (Citronella 25%) - 0.2 min.

In addition to mosquito repellant, it makes sense to take other precautions against insect bites – cover as much skin as possible with loose, light-colored clothing and a hat. Remove any standing water (the ideal breeding place for mosquitoes) from yards, campsites and other outdoor areas as soon as possible. If you will be exposed to mosquitoes for long periods of time, consider adding using mosquito netting to your defensive lineup. Some of the nets are even available pre-treated with repellant. At home, be sure your window and door screens are tight and free of holes.

By following these common-sense guidelines and using the appropriate product for your location and activity, you’ll be able to enjoy your outdoor summer activities with fewer worries. One final tip: watch for mosquitoes landing on you, but not biting - this is a sign that your repellant is beginning to wear off. Remember to use all insect repellant products as directed, and enjoy the great outdoors this summer!

This article includes information from the US Centers for Disease Control and Prevention.

For more on this topic, see the HealthLink article West Nile Virus: Here To Stay.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.