As we head toward the heart of mosquito- and tick-bite season, you might want to ponder the findings of new Consumer Reports research into insect repellent sprays:
With one big exception, the so-called “natural” products seriously underperform formulations based on DEET and other synthetics.
The CR lab tested 16 products for their efficacy in discouraging two kinds of mosquitoes – one from the the day-biting Aades genus, which can carry the Zika virus, and one from the night-biting Culex, which can transmit West Nile – as well as the deer ticks of such concern in this part of the world because they spread Lyme disease and other nastiness.
The testing was straightforward in a mildly horrifying way:
Our brave testers stuck their arms into cages full of disease-free female mosquitoes in need of a blood meal to lay their eggs, and then watched and recorded bites for five minutes every hour. A repellent failed if a tester was bitten two or more times in one 5-minute session, or once in two consecutive sessions.
For ticks, we marked each tester’s bare arms with three lines, then released, one at a time, five disease-free deer ticks to crawl on them. The repellent failed if two ticks crossed into the treated area. Some products protected against two common types of possibly disease-carrying mosquitoes and deer ticks for several hours, and they earned our recommendation.
Six of the tested repellents were based on natural substances, primarily aromatic plant oils thought to have insect-repelling properties. All but one ranked at the bottom of the list of 16 as their protective effect faded rapidly, in some cases lasting less than an hour.
Only one synthetic product, containing 5 percent DEET, performed so poorly.
The top-rated sprays gave protection for eight hours or more, which is a long time to offer your arm to mosquitoes and ticks, even if they are disease-free.
Heading the list was a pump spray by Sawyer with a 20 percent concentration of picaridin, a newer synthetic repellent that CR says is “modeled after a compound that occurs naturally in the black pepper plant.”
It doesn’t cause the skin irritation sometimes associated with the World War II-era DEET, nor does it dissolve certain plastics as DEET can.
No. 2 was a Ben’s aerosol containing 30 percent DEET, followed closely by a Repel product based on 30 percent oil of lemon eucalyptus, in a pump spray.
(As it happens, we use a 40 percent version of the Repel product on the sailboat, so I can attest that it has a pleasant aroma even if the close quarters of our tiny cabin, and seems to work against everything but the lake-fly hatch that settles over Lake Pepin like a gooey blizzard every spring. And it doesn’t numb your lips if you misapply.)
Interestingly, the performance differences among the top three products as measured by CR were slight. Each was scored by the number of hours it warded off the three insects; adding the scores together, I get 24.5 for the Sawyer, 24 for the Ben’s, 22 for the Repel.
A two-spray strategy?
Nearly all of the advantage for Sawyer and Ben’s came in their performance against ticks, so I suppose a person could use the DEET or picaridin on their socks and pants legs and reserve the Repel for direct application to skin and hair and such if they find the synthetics unpleasant (as I admit I do with DEET).
Comparing them on price per ounce – this is Consumer Reports, after all – the Sawyer was most expensive at $2.06, followed by Repel at $1.88 and Ben’s at $1.33.
A few more points to keep in mind when you go shopping:
- The list of nonworking natural repellents was long: forget about oils of cedar, lemongrass, rosemary – even, surprisingly, citronella.
- If key ingredients matter, so does concentration – as demonstrated by the 20-percent-plus formulations of the top tier. A picardin-based product led the field, but a 5 percent picardin product was the only synthetic to test as poorly as the ineffective natural sprays; it held off the Aades skeeters for a mere half-hour.
- Inactive ingredients can matter, too, apparently – at least in the case of a 15 percent DEET product that was more effective against deer ticks than a competitor’s 25 percent product. But you can’t count on shopping for that particular magic bullet because the U.S. Environmental Protection Agency doesn’t require that inactives be listed.
Oh, and those supposedly insect-repelling wristbands that take spraying out of the picture entirely?
Consumer Reports found them so ineffective as a group that they didn’t even bother publishing comparative findings from their tests.
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The magazine’s full article and ratings on insect repellents can be found here and at this writing you don’t have to log in as a subscriber to see them, which is unusual. If that changes between my writing and your reading, a slimmer version should still be accessible here.