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Do Sunscreen and Insect Repellent Cancel Each Other Out?

WebMD Health News

Aug. 4, 2000 -- Sunscreen not only wards off sunburn but protects our skin from the sun's cancer-causing effects. And certain insect repellents not only stop itchy bug bites but guard against infection with insect-borne diseases like Lyme disease and, now, West Nile virus.

But three years ago, insect repellent containing the very effective ingredient DEET was shown to reduce the potency of sunscreens by a third. So what's an outdoors-lover to do?

A new study from the U.S. Army may only add to the confusion: It found that sunscreen, conversely, does not seem to decrease the effectiveness of insect repellent. Still, the researchers and other experts say, the take-home message is to keep using both, and they offer some tips on how to stay bite- and burn-free.

"On the basis of our research, it's impossible to know how different brands of sunscreen interact with different brands of insect repellent, because there's thousands of possible combinations," says Capt. Michael Murphy, MC, USA, author of the study published in the Journal of the American Academy of Dermatology. "But the findings can still help you to make an informed decision about whether to combine sunscreen and insect repellent," says Murphy, a dermatology resident at Walter Reed Army Medical Center in Washington.

It's not always an easy decision. Lyme disease is a tick-borne bacterial infection that causes a skin rash and flu-like symptoms, and, if left untreated, can lead to heart problems and arthritis. The number of infected ticks is thought to be increasing, so the CDC recommends using repellent containing DEET when working or playing in wooded areas. "DEET also plays an important role in preventing West Nile virus," the mosquito-borne disease that killed seven people in the New York area last summer, Murphy adds.

Similarly, doctors say sunscreen is one of the best ways to prevent skin cancer. "Skin cancer is an epidemic in the U.S.," says Roger Ceilley, MD, a past president of the American Academy of Dermatology and clinical professor at the University of Iowa School of Medicine. "Somebody dies of melanoma every hour, yet most of these deaths can be prevented with hats and sunscreen," he says.

So what exactly should do you protect yourself this summer? "Probably the best approach is to wear lightweight long sleeves and long pants, then spray them with DEET," Ceilley tells WebMD. "That way, you're protected against Lyme disease and skin cancer.

But, he advises, you should still wear insect repellent and sunscreen on exposed skin as follows:

  • Choose an insect repellent that contains DEET, such as Off! or Cutter's.
  • Choose a sunscreen with a sun protective factor (SPF) of at least 30.
  • Apply the sunscreen and repellent thoroughly and evenly, about 10-15 minutes apart.
  • Reapply the sunscreen frequently to offset perspiration and humidity.

To shed more light on use of the combination, Murphy and colleagues looked at the effects of both cream and gel sunscreen on insect repellent. They compared the effectiveness of insect repellent alone, repellent applied five minutes before sunscreen, and repellent applied five minutes after sunscreen.

Twenty adult study participants were exposed to two species of mosquitoes. With a test cage, containing the mosquitoes, attached to participants' arms, the insects were given the opportunity to feed at two-hour intervals over 10 hours.

The data showed that insect repellent is effective for up to 10 hours, whether applied alone or used before or after sunscreen.


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