DEET is not the only insect repellent that works, but may be the most effective against the widest range of bugs. It is also a synthetic chemical with known and suspected adverse effects on human health.
That makes for a quandary. Should you use products made with DEET or try a newer—or natural—alternative: in particular, Picaridin, lemon eucalyptus oil or soy oil? There is no one-size-fits-all answer, but following are the things to consider when making your choice.
THE FACTS ABOUT DEET
Toxicity: According to the Environmental Protection Agency (EPA), the "acute toxicity" of DEET is low, meaning adverse effects are mild and temporary—mainly rashes. A few cases of seizures have been reported, but the link to DEET is inconclusive, says the EPA.
So far so good. However, the EPA's safety review was conducted in the 1990s, and the research it was based on did not adequately explore chronic toxicity. More recent research shows that DEET is a neurotoxin and could have long-term effects. Moreover, DEET may increase the toxicity of other chemicals to which people are exposed. For instance, people wearing DEET more easily absorb 2,4-D, a toxic weed killer that was used in Agent Orange and is now commonly used on lawns (where a DEET-slathered individual might be).
Clearly, more research is needed into the long-term health effects of DEET—especially on children. (One third of children in the U.S. are estimated to use DEET-based products.)
Also note that there are additional risks from very high doses of DEET and prolonged exposure. The National Institutes of Health says the high levels to which military personnel or game wardens might be exposed could lead to severe skin reactions (blisters, burning and scars), insomnia and mood changes. Completely improper use, such as swallowing, has its own, serious hazards.
Concentration: In the U.S., you can buy products with up to 100% DEET, but NRDC senior scientist Gina Solomon recommends 30% or less. While protection time increases with higher concentrations, it plateaus by 50%, and the protection afforded by 30% is sufficient for almost all circumstances. In Canada, 30% is the legal limit.
Safe usage: The EPA believes that "the normal use of DEET does not present a health concern to the general U.S. population." But "normal use" does not really mean normal use. It means careful use of a prescribed kind. That's why the EPA requires the following text on all product labels:
• Do not apply over cuts, wounds, or irritated skin.
• Do not apply to hands or near eyes and mouth of young children.
• Do not allow young children to apply this product.
• Use just enough repellent to cover exposed skin and/or clothing.
• Do not use under clothing.
• Avoid over-application of this product.
• After returning indoors, wash treated skin with soap and water.
• Wash treated clothing before wearing it again.
Labels on sprays must also say:
• Do not spray in enclosed areas.
• To apply to face, spray on hands first and then rub on face. Do not spray directly onto face.
If you decide to use DEET, do follow these instructions for safety.
Age of user: Notwithstanding the special precautions recommended for children above, the EPA has approved DEET for use on children of any age at any concentration.
The American Academy of Pediatrics recommends more caution. It advises no DEET for infants under two months and a maximum concentration of 30% for children over two months (which, to reiterate, is a good cap for adults too). Duke University pharmacologist Mohammed Abou Donia says to avoid DEET on infants altogether for two reasons. First, a baby's skin is too thin to act as a barrier to absorption. Second, babies cannot metabolize chemicals as well as older children and adults.
As many substances that affect kids can also affect fetuses, pregnant women may want to consider the possible risks to children in connection with their own use of DEET.
NEWER—AND NATURAL—ALTERNATIVES
Picaridin: Picaridin has been widely used in other parts of the world, and has been available in the U.S. in a variety of brands since 2005. Structurally based on chemicals in pepper, it appears to interfere with the mosquito's ability to smell its prey. The chemical is extremely effective for some species of mosquito (including important disease-carrying mosquitoes such as A. aegypti), but is less effective for other species that don't appear to rely on smell, so overall it may be somewhat less effective than DEET. A 20% Picaridin formulation has been shown to repel mosquitoes for 8-10 hours.
Picaridin is much less irritating to the skin than DEET, so it might be a better choice for people with sensitive skin. It has very low toxicity and does not appear to cause adverse neurological or reproductive effects. Nor does it cause cancer in animals. It also lacks the unpleasant odor of DEET.
Natural alternatives: Studies have shown that oil of lemon eucalyptus and soy oil perform comparably to many DEET-based products. A recent Consumer Reports study found one commercial preparation with lemon eucalyptus was effective for seven hours. Note that use of lemon eucalyptus is not advised on children under three. It is important to remember in this context that the fact that a chemical is natural, not synthetic, does not necessarily mean it is safe.
Other natural repellents have been shown in tests to be very short-lasting. Some lose efficacy in less than 20 minutes and cannot be considered practical options.
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