Do You Know Which Mosquito Repellents Really Work? Most People Are Wrong

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Many Americans surveyed in June on how to protect themselves from mosquito-borne diseases like Zika, dengue, and Chikungunya, are ill-prepared. The June survey by Spectrum Brands Holdings (NYSE: SPB), showed that respondents were extremely over confident about their knowledge. While almost a quarter of participants could not name even one effective active ingredient in insect repellents, 82% incorrectly believed that specific products were effective.

Knowledge of insect repellents

Honest bug spray - by Mike Mozart, JeepersMedia, CC BY 2.0

Honest bug spray – by Mike Mozart, JeepersMedia, CC BY 2.0

As explained in yesterday’s post about the survey results, many participants lacked even basic knowledge about what repellents are effective, although they were confident in their knowledge. Almost all were unfamiliar with some effective insect repellent ingredients, especially picaridin and IR3535, although most recognized DEET. More troubling is that “natural” ingredients as citronella, were believed to be effective by 73% of respondents, although they are not.

Why the confusion? The topic is not easy to understand and, more importantly, marketing seems very misleading. Here’s what you need to know.

What insect repellents are the most effective?

Mosquitoes are attracted to people by the scent of several chemicals we produce1: lactic acid and 1-octen-3-ol, two skin compounds produced by our metabolism and sweating, and carbon dioxide, which we exhale. One interesting study from New Mexico State University published open access in the Journal of Insect Science, found differences in results between Aedes albopictus and A. aegypti, the two species of mosquito that are most likely to carry these diseases, with albopictus less attracted to the test subject’s hand.

Let’s look at the best repellents. DEET has long been the “go to” for a serious insect deterrent, and was first developed by the army to protect soldiers. DEET affects mosquitoes’ receptors, preventing them from detecting people, explained Kathy Cearnal, senior director of R&D for Cutter and Repel insect repellent lines. Its most common side effect is rash—and in high concentrations, will melt the plastic on cameras, binoculars, and some synthetic clothing. Despite many people’s wariness, DEET has not been shown to be carcinogenic nor to cause birth defects, despite decades of use. Children are more sensitive, and lower concentrations and frequency of use are recommended, especially for the very young. There have been rare cases of seizures, mostly after drinking DEET. Drinking alcohol can also increase absorption. DEET should NOT be applied under clothing.

Picaridin, a chemical found in plants that produce black pepper. It also works by blocking our scent, but does not kill the insects, and is effective against mosquitoes, biting flies, ticks, fleas, and chiggers. Picaridin’s main side effect is skin irritation; it is also toxic to fish.

IR3535 is active against mosquitoes, deer ticks, body lice, and biting flies. It’s been used in Europe for more than 20 years with no serious adverse effects seen.

Oil of eucalyptus, or p- Menthane-3,8-diol, is a pesticide made from the lemon eucalyptus plant, targeting mosquitoes, biting flies, and gnats. Cearnal says the mosquitoes are repelled by the smell. Eye irritation is the most common side effect.

Other repellents

Activity of some depends on frequency of application and on the type of prep.

For example, Avon Skin So Soft Bug Guard (10% Citronella) reduced attraction of Ae. albopictusup to 120 min after application, but Avon Skin So Soft bath oil (unknown ingredient) had no effect.

EcoSmart Organic Insect Repellent also worked against Ae. albopictus for 240 min, but rapidly lost effectiveness on Ae. aegypti.

A 0.5 ml application of pricey Victoria Secret Bombshell was effective for 2 hours in the small test.

A skin patch containing thiamine (vitamin B1) was ineffective.

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