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Insect Repellents

Topic Overview

You can lower your chance of being bitten by an insect or spiderlike animal (arachnid) by using insect repellents. Mosquitoes, biting flies, and ticks can cause annoying bites and sometimes a serious disease. Mosquito bites can spread infections such as West Nile virus , a virus that causes swelling of the brain ( encephalitis ), and malaria in some parts of the world. Tick bites can cause serious diseases such as Lyme disease and Rocky Mountain spotted fever . Bites from biting flies are painful and may cause a skin infection .

You can buy many different kinds of insect repellents. Some work better than others. DEET provides the longest-lasting protection against mosquito bites. 1

If you have a question or concern about the use of insect repellents, or if you are pregnant or nursing, talk with your doctor.

Products that work the best

DEET (N,N-diethyl-3-meta-toluamide) is the most effective insect repellent.

  • A solution of 23.8% DEET provides about 5 hours of protection from mosquitoes. 1 DEET is available in varying strengths up to 100%. Research shows that strengths greater than 50% do not provide substantially higher protection. Unless you are in areas with a large number of mosquitoes, repellents with 10% to 24% DEET should keep most mosquitoes away from your skin.
  • Concerns have been raised about safety, because DEET is applied to the skin. Studies over the past 40 years haven't shown that DEET causes cancer or other illnesses.
  • Experts disagree about the safest concentration of DEET to use on children. No serious illness has been linked to the use of DEET in children when used according to the product recommendations. The American Academy of Pediatrics (AAP) and other experts suggest that it is safe to apply DEET in concentrations of 10% to 30% DEET to children older than age 2 months. When applying DEET to children 2 months to 24 months of age:
    • Use only when there is a high risk of insect bites.
    • Use repellents with the lowest concentration of DEET available (usually 10% to 30%).
    • As with all insect repellents, use DEET sparingly, and never apply to the hands or near the eyes.
    • Apply no more than 1 time a day, and avoid prolonged use.
  • When applying DEET to children 2 years to 12 years of age:
    • Use repellents with the lowest concentration of DEET available (10% to 30%).
    • Apply no more than 3 times a day, and avoid prolonged use.
  • If you are pregnant or breast-feeding and have concerns about the use of DEET, talk with your doctor. There is no evidence that the use of DEET by pregnant or lactating women poses a health hazard to developing babies or children who are breast-feeding.
  • Do not use DEET products that are combined with sunscreen. Sunscreen needs to be applied more often than DEET.
  • DEET reduces how well sunscreen works by one-third. 2 If you need to use sunscreen and DEET at the same time, put on sunscreen first and wait 20 minutes before applying DEET. Do not use DEET on skin that will be covered by clothing.
  • DEET should also be used carefully on clothing. DEET may damage some synthetic fabrics as well as plastic watch crystals and eyeglass frames.

Picaridin is an insecticide that has been available for use in Europe for many years. It is available in the United States in a 7% concentration spray. It may work as well as DEET in repelling insects. Higher-strength concentrations that are sold in Europe protect against mosquitoes for up to 8 hours. Picaridin is odorless and does not feel sticky or greasy. It is less likely to cause skin irritation than DEET. And it does not damage synthetic fabrics or plastics. The American Academy of Pediatrics (AAP) does not recommend the use of Picaridin on children younger than age 2 months.

Permethrin is a plant-based insecticide that works on contact. You spray it on clothing and other fabrics, such as mosquito netting and tent walls. Permethrin should not be applied directly to the skin. When it is combined with DEET, permethrin provides even better protection against mosquitoes. Permethrin keeps working even after you wash your clothes. You can buy clothes that already contain permethrin (such as BugsAway, Bug Shield, or Buzz Off) to help protect against mosquito bites.

P-menthane-3,8-diol. This insect repellent is commonly known as lemon eucalyptus oil. When oil of lemon eucalyptus was tested against mosquitoes found in the U.S., it provided protection similar to repellents with low concentrations of DEET. It provides up to 2 hours of protection against mosquito bites. Do not apply more than 2 times a day. And do not use this product on children younger than 3 years.

Soybean oil. Insect repellents that contain 2% soybean oil provide 1 to 4 hours of protection from mosquitoes when applied to the skin. Soybean oil is safe to use on infants and children.

IR3535. This repellent is a chemical similar to the amino acid alanine. Tests have shown that it can protect against mosquito bites for up to 1 hour. 1

Products that don't protect against bites for long periods of time

Citronella is a lemon-scented oil, derived from a plant, that repels mosquitoes. It is not as effective or as long-lasting as DEET. The product can be reapplied frequently to increase its effectiveness. Citronella can be found in lotions or in candles for outdoor use. Citronella applied to the skin provides 15 to 20 minutes of protection from mosquitoes. There is no scientific evidence that citronella candles are effective.

Other plant oils. Other plant oils, such as lavender and geranium, provide less than 30 minutes of protection against mosquitoes. These products aren't recommended.

Products sold as repellents that don't work well to prevent bites

There are other products advertised as mosquito repellents that don't effectively prevent mosquito bites. These include:

  • Electronic (sometimes called ultrasonic) devices.
  • Electrocuting devices, which are often called "bug zappers."
  • Mosquito traps.
  • Geranium house plants.
  • Citronella candles.
  • Taking thiamine (vitamin B1) supplements.
  • Skin moisturizers that don't contain approved insect repellents.
  • Wrist, ankle, and neck bands that contain repellents, such as DEET or citronella.

How to use insect repellent safely

Read and follow all instructions on the label. The U.S. Environmental Protection Agency (EPA) recommends the following precautions for using insect repellents:

  • Apply repellents only to exposed skin or clothing as directed on the product label. Do not use under clothing.
  • Never apply a repellent to cuts, wounds, or irritated skin.
  • Do not apply to the eyes and mouth, and apply sparingly around the ears. When using sprays, do not spray directly into your face. Spray on your hand first, and then apply to your face.
  • Do not allow your child to handle the product, and don't apply the repellent to your child's hands. When using a repellent on your child, apply it to your hands and then put it on the child.
  • Do not spray in enclosed areas, such as inside a car. Avoid breathing a repellent spray, and do not use it near food.
  • Use just enough repellent to cover exposed skin or clothing. Heavy application and saturation generally isn't necessary for effectiveness. If biting insects don't respond to a thin film, apply a bit more.
  • After returning indoors, wash treated skin with soap and water and then bathe. This is particularly important when repellents are used repeatedly in a day or several days in a row. Also, wash treated clothing before you wear it again.
  • If you think you or your child may be having a reaction to an insect repellent, stop using the repellent, wash treated skin, and call your doctor or local poison control center. If you see your doctor, take the repellent with you.

References

Citations

  1. Fradin MS, Day JF (2002). Comparative efficacy of insect repellents against mosquito bites. New England Journal of Medicine, 347(1): 13–18.
  2. Committee to Advise on Tropical Medicine and Travel (2005). Statement on personal protective measures to prevent arthropod bites. Canada Communicable Disease Report , 31: 1–20. Available online at http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/05vol31/asc-dcc-4/.

Credits

By Healthwise Staff
E. Gregory Thompson, MD - Internal Medicine
W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Last Revised August 20, 2012

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