Does your mosquito repellent actually work? Researchers have the results

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From ingesting iron pills and drinking gin and tonic to hanging Ziploc bags filled with water and pennies, researchers Stacy Rodriguez and Immo Hansen have found that people try all kinds of home remedies for repelling mosquitoes.

These are just a sampling of creative, and largely unproven, mosquito-repellent strategies that the New Mexico State University researchers and their team compiled in a recent study, published in the peer-reviewed journal PeerJ. The study involved an online survey of more than 5,000 participants from around the world and revealed a long list of unconventional methods that the researchers say warrant further research into their effectiveness. (The list included burning a variety of materials, from animal dung to vanilla candles, ingesting substances from brewer’s yeast to aloe vera and spraying various concoctions such as a mix of beer, mouthwash and Epsom salt or boric acid and sucrose.)

Yet, as Rodriguez and Hansen discovered in previous studies, even some of the more popular and conventional mosquito repellents found on store shelves work no better than doing nothing at all. The researchers have tested a variety of commercial products, such as wearable devices, sprays containing essential oils, vitamin B-containing skin patches and citronella candles. Many of these were of little to no help, but they found the ones containing DEET and oil of lemon eucalyptus were most effective at protecting against mosquito bites.

“There’s a lot of products out there that advertise [they] protect you from mosquitoes, but you as a consumer should be a little bit more proactive and look for active ingredients that actually work,” says Rodriguez, laboratory manager at the Molecular Vector Physiology Lab at New Mexico State University.

Mosquitoes are attracted to the carbon dioxide we exhale, and to the molecules that are created when our skin bacteria break down components of our sweat, Hansen, an associate professor of biology, explains. Some people are particularly attractive to mosquitoes because of the individual composition of bacteria they have and their metabolism, he says.

The insects have odour receptors and they’re specialized in what they can smell, he adds. So some tactics, for example, ingesting garlic, have no effect on repelling them. “You’re going to repel other people, but not mosquitoes,” Hansen says.

DEET, however, binds to specific odour receptors of mosquitoes and over-activates them, he explains.

“Over-activating them is as bad as blocking them completely. Without smell, they can’t switch from host-seeking to biting mode,” Hansen says.

He adds DEET works to repel various species of mosquitoes and most biting insects. The researchers pointed out in one of their studies that DEET has been used for about 70 years and is considered very safe.

Not all repellents work the same way, however. Hansen says unlike DEET, not all have a known receptor that they target.

Rodriguez, Hansen and their team had volunteers test various commercial repellents in the lab to see how well they kept away Aedes albopictus, the mosquito known for transmitting dengue fever, and Aedes aegypti, known for spreading dengue as well as the Zika virus. These species are not typically found in Canada, although in recent years, officials have reported capturing a few Aedes albopictus and Aedes aegypti in the country.

Of the wearable devices they tested, only OFF! Clip-On reduced mosquito attraction rates, the researchers reported. The other devices used active ingredients such as geraniol and geraniol oil, while OFF! Clip-On released the repellent Metofuthrin.

In the same study, they found citronella candles did not protect against mosquitoes, Rodriguez says.

In a different study, spray-on repellents that contained neither DEET nor oil of lemon eucalyptus had limited to no effect. (The researchers found Avon Skin So Soft Bug Guard, which contained oil of citronella, was not very effective against Aedes aegypti, but Avon Skin So Soft bath oil, which had no known active ingredients to repel mosquitoes but is used as a home remedy to ward them off, provided some level of protection that lasted 120 minutes.)

Surprisingly, the researchers found perfume, specifically Victoria’s Secret Bombshell, proved to be a strong repellent that lasted more than two hours, contrary to their prediction that floral fragrances attract mosquitoes. They noted, however, they used a high concentration of the perfume for their research.

Even though icaridin, also known as picaridin, is often recommended as an alternative to DEET, Rodriguez says she did not find it repelled Aedes aegypti, but suggested it may be effective against other mosquito species.

According to Health Canada, certain products, including electrocuting devices, ultrasonic devices and odour-bated mosquito traps, aren’t recommended since they may not be very effective or long-lasting. Health Canada also notes that lanterns and coils are approved to repel mosquitoes from your surroundings, but don’t protect you from insect bites. It advises Canadians to only use approved products that carry a pest control product (PCP) registration number and that are labelled as insect repellents for use on humans (it warns never to use products labelled as insecticides on your body).

Rodriguez’s advice: Stick to products containing DEET or oil of lemon eucalyptus.