Now that mosquitoes can resist DEET, we should, too!

DEET-based insect repellents can be bad news for people. DEET can trigger allergic skin reactions and asthma attacks in sensitive individuals, and has recently been linked to nervous system harm . Still, for a long time, DEET was thought to be the only chemical that could adequately repel mosquitoes that carry dangerous diseases like yellow fever, dengue fever and West Nile virus. But a new study suggests that convention wisdom may be wrong. The research, published early May in the Proceedings of the National Academy of Sciences, found that mosquitoes that carry the yellow fever virus can develop a resistance to DEET and that those mosquitoes can pass the resistant trait down to their offspring.
Apparently, this isn't the first study finding that mosquitoes can become resistant to the toxic pesticide. As far back as 1978, scientists wrote in the Journal of Medical Entomology that some mosquito species could tolerate higher levels of DEET exposure than others, and in 2004, scientists found that the amount of DEET used to repel mosquitoes that carry yellow fever was inadequate at repelling a species of mosquito found in the Caribbean that carries malaria.

The good news is that the Centers for Disease Control and Prevention and other scientists have found safer chemicals that, in some cases, work better than DEET against even the most ravenous disease-carrying mosquitoes. In one 2004 study published in the Journal of Entomology, comparing effectiveness of different mosquito repellents, http://www.bioone.org/doi/abs/10.1603/0022-2585-41.4.726?journalCode=ment picaridin, a chemical derived from pepper, was found more effective at repelling yellow-fever mosquitoes than DEET, and oil of lemon eucalyptus was found just as effective as DEET in repelling mosquitoes that carry West Nile Virus. Other plant oils, such as soybean and geraniol (an oil derived from geraniums), have also been found effective at repelling mosquitoes but not as effectively as picaridin and oil of lemon eucalyptus (note: the CDC advises using products that contain oil of lemon eucalyptus as an active ingredient, not the undiluted oil you can buy at natural food stores. The latter isn't as effective alone as it is when combined with other ingredients).

Unfortunately, you have to make a bit of a tradeoff when purchasing insect repellents. The natural brands that disclose all their ingredients use mostly plant oils that haven't been found very effective in scientific studies. Products that use the most effective ingredients, on the other hand, are made by large companies will tell you what the active ingredient is but not any of the other ingredients, which means they could be using hormone-disrupting chemicals like paraben preservatives or phthalates.

Looking for a safe insect repellent for those evenings outside or an upcoming tropical vacation? Give these a shot. They all contain an effective insecticide without any other nasty chemicals like parabens or phthalates:

Badger USDA Organic Anti-Bug Balm
: oils of citronella, rosemary, lemongrass and geranium make you smell sweet to anyone but bugs.

-BiteBlocker contains a 7 percent concentration of soybean oil and geraniol and no toxic chemicals ($5.40/2-oz. bottle).

-BugBands are rubber bracelets treated with geraniol that you can wear on your wrist or attach to a belt loop or ankle if needed; the bands are reusable up to 120 hours ($14.95/4 bands).

California Baby Natural Bug Blend
uses citronella, lemongrass and cedar oils.
-Repel is the only commercially available product sold in the U.S. that contains oil of lemon eucalyptus. While the concentration of the ingredient is high (the more of the active ingredient, the more effective the product), the company doesn't disclose what the additional ingredients in the product are. So you may want to save this product for the occasions when mosquitoes are really unavoidable, like camping trips or hikes in the woods ($11.50/4-oz. bottle).

-Likewise, products based on picaridin, like Natrapel, Cutter Advanced, and Off! Skintastic contain effectively high levels of the active ingredient but don't tell you what else is in the products. You should also save these for deep-woods hiking or other situations where the threat of mosquito-borne illnesses outweighs the risks associated with unhealthy chemicals in personal care products.

A few other tips when applying insect sprays:
- Forgo the sunscreen/insect repellent combos. Insect repellents should be applied only when needed, whereas sunscreens should be reapplied every two hours to protect against skin cancer.

- Take care around your face. You don't want to directly inhale any chemical regardless of how safe it sounds. When you need to apply insect repellent to your face, spray some on your hands first, then rub it on your face.

Caution for Children: Insect repellents of any kind should not be used directly on young children's skin. For safety tips, see this helpful fact sheet from the Palo Alto Medicatl Foundation.
* report on DEET's neurotoxic effects

**Another study finding that picaridin works better than DEET:

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by Emily Main