Will natural repellents actually kill bugs dead?

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During a season when insect repellent is, of necessity, many people's signature fragrance, consumers may be drawn to sprays with more benign-sounding names and scents. An array of these “natural” repellents is widely available — there’s everything from citronella to soybean oil — but their effectiveness at actually keeping the bugs away is still in question.

Scott Carroll, director of Carroll-Loye Biological Research Consulting, an independent company that tests insect repellents, notes the “tremendous variation” in how well these “natural” insect repellents, deemed “minimum-risk pesticides,” work from one person to another: “Anywhere from five minutes to three hours,” he says. Dennis Tracz, founder of a company that makes a pine-oil based repellent, agrees about natural insect repellents’ lack of reliability, since they usually evaporate quickly. “To me,” he says, “[minimum risk pesticides] is code for: ‘They don’t work very well.’” Indeed, companies that market such “minimum-risk” repellents are not actually required to demonstrate how well they work.

Beyond the question of their effectiveness is that of their safety. Currently, many natural insect repellents are exempt from the safety testing that the EPA requires of more standard repellents, such as DEET-based products. The EPA has deemed both their active and inert ingredients safe for the intended use, mainly because they’ve been used long enough in consumer products without incident, says Carroll. (We at ACSH are slightly taken aback by this seemingly cavalier attitude toward these “so called” natural chemicals, when synthetic chemicals — such as bisphenol A (BPA) — are the subject of intense public fear and scrutiny, despite their more evident utility and equally long history of use in consumer products without incident. “BPA has been used without harm for over 50 years,” ACSH staffer Jody Manley points out.)

Perhaps most intriguing but less credible are current studies suggesting that some “natural” repellents have the kind of potency associated not only with DEET but DDT — the insecticide that, despite its detractors, is enduringly effective in lowering the rates of malaria spread by the anopheles mosquito. Garnering the most attention is the pine-oil derivative isolongiflenone, which, in a 2009 study published in the Journal of Medical Entomology, was found to repel mosquitoes and ticks more effectively than DEET. Apparently, the pine-oil derivative has also performed well as a “spatial repellent” of the sort that is sprayed on the walls of homes and on bed nets to deter mosquitoes. If this pine-oil derivative, manufactured by a company called 141 Repellent Inc., truly is effective in this respect, it would be the first non-synthetic alternative to DDT. But this is a big “if.” ACSH advisor Donald Roberts, a retired professor of tropical public health at the Uniformed Services University of the Health Sciences in Bethesda, thinks that the new product “shows real promise.” But he cautions, "Until we have a lot more test data, it would be hard to give a definitive statement."