AMC Outdoors, June 2006
In 1946, the U.S. Army created N,N-diethyl-m-toluamide. Commonly known as DEET, it is the most widely used insect repellent in the world today. It’s also caustic enough to melt plastic, a concern for many outdoor enthusiasts who regularly slather it on their skin. A variety of alternatives are available, including several natural compounds, but how do they stack up? Several recent studies, including a landmark 2002 report in the New England Journal of Medicine (NEJM), compared the relative efficacy of different products on repelling mosquitoes (and by extension, black flies and ticks).
To DEET or not to DEET
Virtually every study conducted on the topic found DEET to be the most effective mosquito repellent, though protection time varied depending on concentration. According to the NEJM study, repellents with a DEET concentration of between 5 and 10 percent provide one to two hours of complete bite protection. Products with a concentration of around 20 percent work for between four and five hours. Protection time rises marginally up to concentrations of 50 percent, but does not improve at levels higher than this.
Most repellents use an ethanol or alcohol base, which steadily evaporates. Repellents that use non-alcohol solutions often last longer, such as Ultrathon by 3M (the same formula used by the U.S. Army). DEET will melt rayon, spandex, and most plastics (a concern with sunglasses or prescription lenses), but does not affect nylon, wool, or cotton. Hundreds of millions of people have used DEET with no documented health concerns, and it is widely considered safe to apply to skin, though excessive application has caused a contact rash in some cases. In 1998, the EPA completed a comprehensive review of DEET and concluded that it poses no health risks when properly applied.
When using DEET, consider the following. You need only a tiny amount for it to be effective. Do not lather it on like sunscreen, or go crazy with an aerosol can or spray bottle. Instead, place a minuscule amount in your palm, rub your hands together, and then run your hands over the areas you want to protect (wash off your hands afterward). Avoid getting DEET in your eyes or near your mouth. For young children, most health experts recommend using a DEET-free repellent.
DEET-free Alternatives
The compound most likely to unseat DEET is picaridin, a synthetic chemical widely used in Europe and Australia (where it is the best-selling repellent). Picaridin-based repellents were only approved for resale in the U.S. in April 2005, and are currently available only in concentrations of less than 10 percent. Picaridin is odorless, safe on plastics, and carries no apparent health risks. Initial studies indicate that concentrations of 7 percent provide roughly two hours of protection. Though not yet available in the U.S., higher concentrations can provide protection levels comparable to DEET; in one study, a 20 percent concentration provided nearly eight hours of bite-free bliss.
When it came to natural bug dopes, the most effective contain oil of eucalyptus, which provides up to two hours of protection. But many of these products, such as Repel’s Lemon Eucalyptus Repellent, also have a powerful scent. It smells better than DEET, but the aroma will slowly permeate all your gear. At home, store it separately from your equipment and keep it in an airtight container.
Next up in effectiveness is soybean oil. According to the NEJM study, products with a concentration of only 2 percent soybean oil conferred roughly 90 minutes of protection. It is available in a handful of repellents, including the Bite Blocker product line. Citronella oil comes from a plant closely related to lemon grass, and is often touted for its anti-mosquito powers. It’s widely available - the Natrapel brand line uses itÑand often marketed as a safe repellent for young children. But it barely works, providing only 10 to 20 minutes of protection, depending on concentration.
- Matt Heid is Senior Editor of AMC Outdoors.
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