To Evolution

A guide for mosquito repellents, from DEET to ... Gin And Tonic?

    Abdulaziz Sobh
    By Abdulaziz Sobh

    Categories: Health


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    Testing the Efficacy of Mosquito Repellents
    A 2015 study tested eight commercial mosquito repellents, two fragrances, and a vitamin B patch by releasing mosquitoes in a sealed chamber with a treated hand. The study found that after four hours, the most effective products containing DEET, as well as a "natural" spray without DEET.
    Editor's Note: This story was originally published in 2016 and has been updated.

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    People make things more difficult in the hope of avoiding mosquito bites. They burn cow dung, coconut husks or coffee. They drink gin and tonic. They eat bananas. They are sprayed with mouthwash or rubbed in a clove/alcohol solution. And they rub with Bounce. "You know, those very perfumed leaves that you put in your dryer," says Dr. Immo Hansen, a professor at the Institute of Applied Biosciences at the State University of New Mexico.

    None of these techniques have been tested to see if they really keep mosquitoes away. But that does not stop people from trying them, according to a study published this summer by Hansen and his colleague, Stacey Rodriguez, laboratory manager of the NMSU's Hansen Lab, which studies ways to prevent mosquito-borne diseases. They and their colleagues asked 5,000 people what they did to protect themselves against mosquitoes. Most conventional mosquito repellents.

    Then, the researchers asked about their traditional home remedies. It was then that the cow dung and the sheets of the dryer came out. In the interviews, Hansen and Rodríguez shared some of the answers they received. His work will be published this summer in the PeerJ peer-reviewed journal.

    Beyond folklore and traditional remedies, there are proven ways to protect against mosquitoes and the diseases they transmit. NPR spoke with researchers, many of whom spend a lot of time in jungles, swamps and tropical areas infested with mosquitoes.

    What repellents work best to keep mosquitoes from biting?
    Products containing DEET have been shown to be safe and effective. DEET is the abbreviation for the chemical N, N-diethyl-meta-toluamide, the active ingredient in many insect repellents. A 2015 article in the Journal of Insect Science examined the effectiveness of several commercial insect aerosols, and products containing DEET proved to be effective and relatively durable. Rodríguez and Hansen were the authors of the 2015 study and replicated the results in a 2017 article in the same journal.

    DEET appeared on store shelves in 1957. There was an initial concern about their safety speculating that it was related to neurological problems. But recent reviews, for example, a study published in June 2014 in the journal Parasites and Vectors, says: "Animal tests, observational studies and intervention trials have not found evidence of serious adverse events associated with the use of DEET recommended. "

    DEET is not the only weapon. Products that contain the ingredients picaridin and IR 3535 are so effective, says Dr. Dan Strickman, with the Global Health Program at the Bill and Melinda Gates Foundation (which funds NPR funds) and author of Insect Bites Prevention, Stings, and Disease.

    The Centers for Disease Control and Prevention recommend repellents with any of these active ingredients as safe and effective. They are widely available throughout the world.

    Actually, Strickman gives Picard the advantage.

    "Picaridin is a little more effective than DEET and seems to keep mosquitoes at a greater distance," he says. When people use DEET, mosquitoes can fall on them but not bite. When they use a product that contains picaridin, mosquitoes are less likely to land. Repellents with IR 3535 are slightly less effective, says Strickman, but do not have the strong smell of other products.

    Then there's the lemon eucalyptus oil, or PMD, a natural oil extracted from the leaves and twigs of the lemon-scented eucalyptus gum plant, also recommended by the CDC. PMD is the ingredient in the oil that makes it insect repellent. The NMSU researchers discovered that a product containing lemon eucalyptus oil was almost as effective and durable as products containing DEET. "For some people, there is a stigma to the use of chemical substances on their skin, they prefer a more natural product," says Rodríguez.

    A surprising finding in 2015 was that a perfume, Victoria's Secret Bombshell, was a pretty good repellent. Hansen and Rodriguez said they added it to the products they tested as a positive control, believing that its floral scent would attract mosquitoes. It turned out that the insects hated the smell.

    His most recent study of 2017 also had a surprise. A product called Off Clip-On adheres to clothing and contains a cartridge that contains the area repellent, metofluthrin, also recommended by the CDC. The portable device is designed for someone sitting in one place, like a parent watching a softball game. The person turns on a small battery operated fan that blows a small mist of repellent into the air surrounding the user with a clip. "It really worked like an amulet," says Hansen. It was as effective as DEET or lemon eucalyptus oil to keep insects away, he says.

    Are there products that just do not work?

    Not all products offer what they promise. The 2015 study found that vitamin B1 patches are not effective in repelling mosquitoes. The 2017 study added citronella candles to the list of products that do not keep mosquitoes away.

    The so-called insect repellent bracelets and bangles do not repel mosquitoes, according to a recent study. These products contain a variety of oils that include citronella and lemongrass.

    "I had mosquitoes landing right on the bracelet I was testing," says Rodriguez. "They market [wristbands and bracelets] as protection against Zika [a virus spread by mosquitoes that, in pregnant women, can cause serious birth defects], but they are completely ineffective."

    Ultrasonic devices, which use tones that people can not hear but marketing specialists claim that mosquitoes hate, do not work, either. "The sonic device we tested had no effect," says Hansen. "We have also tested others before, none of them work, there is no scientific evidence that mosquitoes are repelled by sound.

    How often should you reapply a repellent?
    In general, it is a good bet to follow the manufacturer's instructions, experts said. People who will be outside for one or two hours should be protected with, say, a product that contains a lower concentration of DEET (approximately 10 percent - identified on the label). Those who will be outside in the forest, in the jungle or marshes, should use a higher concentration of 20 to 25 percent and cool every four hours or so, says Dr. Jorge Rey, interim director of the Laboratory of Medical Entomology of Florida in Vero Beach. "The greater the concentration, the longer it lasts," Rey says.

    And again, follow the manufacturer's instructions on the amount used. "A lot of people think that if something is good, a lot is better," says Dr. William Reisen, professor emeritus at the Faculty of Veterinary Medicine at the University of California, Davis. "You do not have to take a bath in things."

    What type of clothing helps protect against bites?
    When Rey conducts research trips to highly infested areas, such as the Florida Everglades, he adapts well. "We wear long pants and long-sleeved shirts," he says. "If it's particularly bad, we use hats with nets that fall over the face, and we depend on the repellent in the exposed areas." That could mean hands, neck, and face. But do not spray your face, experts say. To avoid irritating the eyes, put the repellent on your hands and rub it on your face.

    And do not forget your feet. Mosquitoes have peculiar olfactory preferences. Many of them, especially the Aedes variety that transmits the Zika virus, love the smell of their feet.

    "Wearing sandals is not a good idea," says Rodriguez. Shoes and socks are required, and putting pants in socks or shoes helps prevent mosquitoes from entering clothes. She wears long pants when she is outside in mosquito territory, and definitely not yoga pants. "Spandex is very friendly to mosquitoes, they bite it, I wear pants with pockets and long-sleeved shirts, sprayed with DEET."

    What else can reduce the risk of mosquito bites?
    Mosquitoes can bite at any time of the day, but the Aedes aegypti species that transmits Zika prefers mid-morning and afternoon, says Strickman. If possible, stay inside buildings with mosquito netting or air conditioning during those times.

    Since these mosquitoes in particular breed in stagnant water in containers such as pots, old tires, buckets, and trash cans, people should eliminate the immediate area of things that can accumulate water. "The pools, unless they're abandoned, are fine," says Rey. The chemicals used to keep swimming pools safe also keep mosquitoes away. A close look is needed to find all possible breeding grounds for mosquitoes. "I've seen some developments in a water film next to a sink, or in the bottom of a glass that people use to brush their teeth," says Strickman. Cleaning standing water areas can greatly reduce the number of mosquitoes.

    The more people do that kind of basic cleaning, the fewer mosquitoes there will be. "It may not be perfect, but it will dramatically decrease the number of mosquitoes," says Strickman.

    What is on the horizon to help people avoid mosquito bites and the diseases they bring?

    Hansen says his lab is working on a technique in which male mosquitoes are sterilized with radiation and then released into the environment. They mate with females that lay eggs, but the eggs never hatch. The technique would target specific species, such as Aedes aegypti that transmits Zika, dengue fever, and other diseases.

    And a team of Massachusetts scientists is working on a mosquito repellent that will stay on the skin and remain active for hours or even days, says Dr. Abraar Karan, a physician at Brigham and Women's Hospital. He is one of the creators of Hour72 +, which says it can not penetrate the skin and enter the bloodstream and only fades through the natural shedding of the skin.

    Hour72 + won the $ 75,000 Dubilier Grand Prize at the annual New Venture Competition of the Harvard Business School. Karan plans to further test the prototype, which is not on the market, to see how long it remains effective.