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Insect repellents are safe to use

Copyright 2002 President Fellows Harvard College behalf HMS MediServices Phoby LizGreen HMS MediServices Anthony Leader Komaroff MD Harvard Health Publications

Copyright 2002 President and Fellows of Harvard College on behalf of HMS Media Services, Photo by Liza Green, HMS Media Services, Anthony Leader Komaroff, MD, Harvard Health Publications

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Updated: September 22, 2012 6:10AM

Dear Doctor K: Can you recommend an insect repellent that is safe and effective?

Dear Reader: The itch from mosquito bites — or the yuck factor of pulling a tick off your skin — can be irritating and unpleasant. But even worse are the illnesses that insects can carry, including West Nile virus, Eastern equine encephalitis and Lyme disease.

Many people are just as wary of insect repellents as they are of bug bites. They worry that they are dangerous. But used properly, insect repellents are safe. The most effective ones are:

DEET. If you’re in an area with a lot of ticks or insect-borne illnesses, this is the repellent to use. It really gets the job done.

Lemon eucalyptus oil (or PMD, the man-made version) works nearly as well as DEET against both mosquitoes and ticks, but it shouldn’t be used on children under 3 years old.

Picaridin works well against mosquitoes, but much less well against ticks.

2-undecanone (IBI-246) is good for about four hours against mosquitoes, two hours against ticks. I recommend you avoid reapplying it, because too much exposure to these chemicals could be dangerous. So if you are going to be out for more than four hours, use one of the first three on this list.

IR3535 works for about two hours against mosquitoes and ticks. Again, I recommend you avoid reapplying it.

Permethrin works well, but shouldn’t be sprayed or rubbed on the skin -- just on clothing or mosquito netting.

Other insect repellents on the market include citronella, catnip oil, bug zappers and ultrasonic devices. They may help a little, for a little while. But they can’t compete with DEET and the other repellents mentioned above.

A few safety tips for using insect repellents:

Don’t use them on infants younger than 2 months old (instead, put mosquito netting over the baby carrier).

Apply spray repellent outside so you are less likely to breathe it in (and won’t get it on household surfaces).

Don’t spray a repellent directly on your face. Instead, spray it on your hand and rub some on your face. (Never put permethrin on your face.)

Whenever you use insect repellent, always wash your hands well before eating. (That’s also good advice whether or not you’re using insect repellent.)

Spray the repellent lightly (more is not necessarily better) on exposed skin and clothing. In particular, don’t overdo it with DEET. Apply it lightly on the skin that will be exposed to insects and not covered by clothing.

Write to Dr. Komaroff at

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