Dear Doctor Column, June 27, 2005

CDC Adds to Approved List of Mosquito-fighting Ingredients

Question:

I understand there's a new insect repellent available. Can you tell me what it is?

Answer:

Until spring 2005, DEET-containing products had been the mainstay of effective mosquito repellents and the sole formulation recommended by the Centers for Disease Control and Prevention (CDC). They were the only insect repellents recommended to guard against West Nile virus, an infection that some mosquitoes can carry. Most of the time, the virus leads to no symptoms. Occasionally, people develop mild flu-like symptoms, but in rare cases, it can cause serious health problems, such as West Nile encephalitis and meningitis, particularly in the elderly. Symptoms of severe illness include headache, high fever, stiff neck, mental confusion, muscle weakness, tremors (shaking), convulsions, coma, and paralysis.

CDC has added two new active ingredients to the recommended list — picaridin and oil of lemon eucalyptus. Recent studies demonstrated that picaridin and oil of lemon eucalyptus provide the same level of protection as DEET, which has been used in many brand name repellents for decades.

Picaridin is a compound found in many mosquito repellents used in Europe, Australia, Latin America, and Asia for some time. It is recommended by the World Health Organization for malaria prevention. Its chemical name, which you might find in the list of "active ingredients" on a product, is KBR 3023. In the United States, the first commercially available product contains 7% picaridin and is being marketed under the name Cutter Advanced. Other picaridin-containing products are expected to be available soon.

Oil of lemon eucalyptus also is known as P-menthane diol, or PMD for short. PMD is a plant-based repellent that protects for shorter periods, similar to low concentrations of DEET. CDC cautions that oil of lemon eucalyptus should not be used on children aged 3 or younger, and it has not been tested against the mosquitoes that spread malaria and some other tropical diseases.

A study published in 2002 in The New England Journal of Medicine found that perennial favorites citronella and Avon Skin-so-Soft, as well as DEET-impregnated wrist bands, offered only very short protection times. Of the non-DEET products, a 2% soybean oil product provided up to 90 minutes of mosquito protection. The journal article did not evaluate a picaridin product because it was not licensed for use in the U.S. at the time of the study.

Permethrin is another effective insect repellent, but it should only be applied to clothing, shoes, mosquito netting, or camping gear, not directly to skin. Certain permethrin-containing products are registered with the Environmental Protection Agency (EPA) for this use. Permethrin can retain its effectiveness after repeated laundering, and some clothing and other commercial products are available pretreated with permethrin.

As you consider how to protect yourself and your family against mosquitoes this summer, you will have a wider array of products to choose from that have been proven safe and offer long-lasting protection against mosquito bites. Some of these other products may offer a more appealing smell or feel than the ones that have been available up to now. Whatever repellent you choose, it is a good idea to check the list of active ingredients to make sure one of these chemicals — DEET, picaridin, and oil of lemon eucalyptus — is on the list.

In addition to repellent, EPA and CDC recommend taking the following precautions to guard against mosquitoes and other bug bites:

• Apply repellents only to exposed skin and/or clothing as directed on the product label. Do not use repellents under clothing.
• Never use repellents over cuts, wounds, or irritated skin.
• Do not apply to eyes or mouth, and apply sparingly around ears. When using sprays, do not spray directly on face —spray on hands first and then apply to face.
• Do not allow children to handle the product. When using on children, apply to your own hands first and then put it on the child.
• Use just enough repellent to cover exposed skin and/or clothing. Heavy application and saturation are generally unnecessary for effectiveness. If biting insects do not respond to a thin film of repellent, then apply a bit more.
• After returning indoors, wash treated skin with soap and water or bathe. This is particularly important when repellents are repeatedly used in a day or on consecutive days. Also, wash treated clothing before wearing it again. (This precaution may vary with different repellents — check the product label.)
• If you or your child get a rash or other bad reaction from an insect repellent, stop using the repellent, wash it off with mild soap and water, and call a local poison control center for further guidance.
• Stay indoors at dusk and dawn when mosquitoes are most active.
• Use screens on doors and windows to keep mosquitoes from entering your home. Repair broken or damaged screens.
• Wear long-sleeved shirts and long pants when outdoors whenever possible.
• For children, choose a repellent containing no more than 30% DEET; in higher concentrations, the chemical, which is absorbed through the skin, can be toxic. Be sure to follow directions on the label.
• Do not rely on vitamin B, ultrasonic devices, or other unproven devices to prevent mosquito bites.
• Be sure to eliminate mosquito-breeding areas around your home by removing standing water from gutters, old tires, wading pools, tarps, potted plants, and other outside buckets and pails. Also, be sure water in pet dishes and birdbaths is changed regularly.

CDC Web sites contain more information about the new recommendations and about DEET. Information from the American Academy of Pediatrics about safe use of DEET for children can be found at their Web site.

International travelers should consult the CDC Travelers' Health Web site for more detailed recommendations on the use of insect repellents.