Mosquito repellents not all created equal


Published: Friday, August 1, 2003 at 6:01 a.m.
Last Modified: Friday, August 1, 2003 at 12:34 a.m.
Floridians are all too familiar with the often foul-smelling, oily substances known as insect repellents. Florida is home to 77 species of mosquitoes, and with the threat of diseases like West Nile Virus and Eastern Equine Encephalitis looming, repellent has become a necessary addition to any outside evening activities.
Although the Environmental Protection Agency says that DEET - the most common and most effective chemical in bug repellents - is safe to use, some health-conscious people are wary of drenching themselves in the sprays and lotions that contain it.
And while it's true that a variety of natural alternatives to DEET exist on the market, they might not fulfill their claims of warding off the bothersome bug bites unless wearers are ready to reapply the repellent every few minutes.
In a study published in July 2002 by the University of North Carolina at Chapel Hill and UF's Florida Medical Entomology Laboratory in Vero Beach, various bug repellents were tested and ranked according to how long they repelled mosquito bites.
In the study, test subjects' arms were coated in various bug repellents and then placed into a chamber with some hungry female mosquitoes. Researchers then recorded how much time elapsed before the subjects received a bite.
Not surprisingly, those repellents containing DEET were proven to be most effective. OFF! Deep Woods contained the highest concentration of DEET of any of the products tested with 23.8 percent DEET and warded off mosquitoes for a little more than five hours.
Two natural repellents were tested in the study-citronella and soybean oil.
Citronella was the key active ingredient in seven of the products tested during the study. Though citronella is a common natural repellent to find on store shelves, it protected against bites for less than 20 minutes on average in the study.
On the other hand, a product that contained 2 percent soybean oil actually fared as well as products with low concentrations (4.75 percent) of DEET. Bite Blocker for Kids, the test product containing soybean oil, prevented mosquito bites for about an hour and a half.
However, Jonathan Day, the professor of medical entomology at UF who co-authored the repellent study, said they weren't sure the 2 percent soybean oil was the active ingredient in the Bite Blocker for Kids.
"It was listed as the active ingredient, but there were other things (in it) that were better repellents than soybean oil," he said.
Day said a variety of plant oils, including citronella, soybean, eucalyptus, cedar and vanilla, actually could be good repellents. However, he said the problem arises with the concentration of the oils used in the bug repellents. Day pointed out that when using botanical repellents, you really are using chemicals, but they are the natural chemicals plants have developed over time. And these chemicals could be just as harmful as DEET when used in high concentrations.
"The higher the concentration (of natural repellent), the more irritating this stuff is going to be," he said. "That's why you tend to see botanicals with very low concentrations of these active ingredients."
Some of the citronella products tested contained only 0.05 percent citronella. Though the citronella might initially ward of bites, such a low concentration quickly wears off.
"In some of these citronella products, in order to get the repellent effect, people would have to reapply (the repellent) six times an hour," he said.
Side effects from DEET are rare and usually result from either inhalation or eye contact with the repellent. Some people may have allergic skin reactions to DEET, but these cases are also rare, and so Day stands by DEET's effectiveness in preventing bites.
"The adverse affects of DEET have come from people who abuse it," he said. "As long as it's used according to label instructions, it's not a problem."

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