April 10, 2012
The Toxic Truth About DEET and Permethrin - 4
by Tim MacWelch
Many people respond to their fears of West Nile Virus and Lyme Disease (as well as their annoyance of chigger bites) by slathering on insect repellent, and quite often drenching their children in the stuff too. The prevalent choice in most stores will be a DEET-based repellent, which has proven effective at repelling bugs in study after study.
But here’s the problem: DEET- and Permethrin-based repellents aren't just hazardous to ticks, mosquitoes and other pests; they may be hazardous to us, too.
DEET, a registered pesticide, is short for N,N-diethyl-meta-toluamide and is a member of the toluene chemical family. Toluene is an organic solvent that can be absorbed through human skin, where it passes into the blood stream. The Medical Sciences Bulletin, published by Pharmaceutical Information Associates Ltd. reports, “Up to 56 percent of DEET applied topically penetrates intact human skin and 17 percent is absorbed into the bloodstream.” Blood concentrations of about 3 milligrams per liter have been reported several hours after DEET repellent was applied to the skin as directed. DEET is also absorbed by the internal organs.
The most serious concerns about DEET are its effects on the central nervous system. One Duke University study showed that lab animals exposed to the equivalent of the average human doses of DEET performed far worse than untreated animals in motor skills tests. The study also found that combined exposure to DEET and permethrin can lead to both motor deficits and learning and memory dysfunction.
If that wasn’t bad enough, DEET might have significantly greater toxicity when combined with ethyl alcohol, isopropyl alcohol and freon, all of which can be components in some DEET repellents.
Don’t think Permethrin is any better, either. Permethrin is topical insecticide, which is not known to rapidly harm most mammals or birds, but is dangerously toxic to cats and fish. It has a low mammalian toxicity and is poorly absorbed by skin, which has prompted its use to treat head lice and nits, scabies, and various species of ticks. But the strikes against it are significant. Peremthrin is a suspected carcinogen, endocrine toxicant, liver toxicant, neurotoxicant and reproductive toxicant.
If you do decide to use DEET, its best to wear long sleeves and long pants, when possible, and apply the repellent to your clothing, rather than your skin, to reduce your exposure. Use the DEET-based products sparingly, as saturation does not increase their efficiency. Never inhale DEET repellents. Repellent-treated clothes should be washed, or kept outside of living areas to reduce your exposure. Following all these precautions reduces your exposure and risk, but does not eliminate it.
If you decide to treat your gear and clothing with Permethrin, follow the directions to the letter. Spray the items outdoors, and do not touch them until dry (2 to 4 hours). Cover your face, or breathe through a mask to avoid inhalation while spraying Permethrin. Do not treat the inside of tents, sleeping bags, gloves, or any other gear that will be in direct contact with your skin.
There are a number of effective, less toxic insect repellents on the market. You can also whip up your own with essential oils available at your local health food store. These natural repellents need to be applied more frequently than DEET-based repellents, but they do not carry the same health risks. Two botanical repellents that performed particularly well in a Florida study were Repel Lemon Eucalyptus Lotion Insect Repellent (also marketed as FiteBite Plant Based Insect Repellent), which protected for 120 minutes, and Bite Blocker for Kids, a 2-percent soybean oil formula, which was effective for 95 minutes. Citronella products in the study provided about 30 to 40 minutes of protection.
Look for repellents made from essential oils that include citronella, teatree, pennyroyal, cedar, and eucalyptus, but be aware that these are volatile oils that can trigger allergic reactions in some people, particularly the chemically sensitive. For those really sensitive folks, mesh “Bug Shirts” and head nets are an excellent, non-toxic method of protection.