Apr 10

Study Finds Some Mosquito Repellents Don’t Work

Woman spraying insect repellent on skin, outdoor
Woman spraying insect repellent on skin, outdoor

Every spring and summer, there’s one urgent question on everyone’s mind: which mosquito repellent is best? It seems like there are new brands and formulas coming out every season, and countless websites and researchers do regular tests to find the answer.

This year, a new study published in the Journal of Insect Science compared wearable devices and spray-on repellents to see which ones were most effective at repelling Aedes aegypti, which are public enemy number one in the Zika epidemic.

They tested 11 different products (five wearable devices, five sprays, and one candle) on two volunteers and then measured the movement of mosquitoes around the subjects. The scientists, affiliated with New Mexico State University, found that several of the repellents aren’t very effective at all.

An article in Consumer Reports explains the results of the study and how they compare to other tests.

  • Four out of the five tested wearable devices, which included three brands of wrist bands and two clip-on repellers, did nothing to repel mosquitoes.

  • A citronella candle, placed on the ground next to the volunteer, also failed to ward off the insects.

  • Out of five spray-on repellents—including ones containing deet, oil of lemon eucalyptus (OLE), picaridin, and natural plant oils— those with deet and OLE were the most effective by far.

Repellents Are Everywhere

Last year’s Zika outbreaks have been a boon to the insect repellent industry. Last summer, at the height of mosquito season, insect repellent sales were up by 648 percent. In August, an Amazon search using the keywords “mosquito repellent” turned up more than 13,000 products. Today, that same search turns up closer to 25,000 products—not just sprays, but also creams, clothing, skin patches, wearable devices (some of which work by emitting noises), and even live plants rich in essential oils.

The sheer number of options presents a doubled-edged sword for consumers: It’s good to have choices, but it’s difficult to know what works and what doesn’t. “The recurrent outbreaks of arboviruses like dengue, chikungunya, and Zika have created a large market for a variety of mosquito repellent and control products,” says Immo Hansen, a scientist who studies vector-borne disease control at New Mexico State University and the principle scientist behind the new research. “But in many cases the claims made by the vendors of these products are exaggerated or outright false.”

To separate the good products from the ineffective ones, Hansen’s lab and Consumer Reports have each been testing these products.

Bracelets and Clip-ons

Hansen’s lab and Consumer Reports have both found that wristband repellents (most of which contain a mix of plant oils and so qualify as natural products) don’t work. Consumer Reports tested two of these products in 2015; Hansen’s new study tested three different ones.

Hansen’s team also tested the Off! Clip-On repellent, a device that attaches to your waistband, belt, or purse and uses a fan to circulate the repellent chemical metofluthrin through the air around you. They found that the product was highly effective at repelling mosquitoes.

But our own testing came to the opposite conclusion: We tested this same device and found that it offered far less protection than our best-performing spray-on repellents.

Consumer Reports doesn’t recommend the Off! Clip-On, not only because it performed poorly in our tests but also because metofluthrin is classified by the EPA as a neurotoxin and a potential carcinogen. In addition to that concern, the Centers for Disease Control and Prevention has said that wearable foggers like this “have not been adequately evaluated for their efficacy in preventing vector-borne diseases.”

Products Containing Deet

Hansen’s finding that deet might offer some of the best protection against mosquitoes agrees with Consumer Reports’ testing, where deet-based repellents consistently earn some of the highest ratings. But while Hansen tested sprays containing 50 percent and 95 percent deet, Consumer Reports advises using only those repellents containing 30 percent or less deet. (in our most recent tests, out of 16 repellents, a product containing 30 percent deet received the second-highest score).

Our experts have long advised that products containing more than 30 percent deet could increase your risk of health effects (including skin rashes, disorientation, and seizures) without offering any more protection than concentrations of 30 percent or lower. That stance has been echoed by the CDC, which advises consumers opting for deet-based repellents to stick to products that contain 20 to 50 percent of active ingredient.

Natural Repellents

Hansen’s test found that Kid’s Herbal Armor—a natural repellent that contains a mix of plant oils—performed as well as a 40 percent deet solution. But in our tests, that same product performed far worse than any deet or picaridin-based repellents.

In fact, Consumer Reports has tested several natural repellents made with similar active ingredients, and found that they are not effective at preventing mosquito bites. Unlike deet, OLE, or picaridin-based products, natural repellents are exempt from Environmental Protection Agency registration, meaning they aren’t required to submit any data to the agency proving that their products work as advertised.

The CDC thinks that that consumers should stick to EPA-registered repellents, and we agree.

If you need more than insect repellent to fight the bite in your backyard, contact DC Mosquito Squad today. We can help keep mosquitoes away so you can savor time outdoors sans bug bites.

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